LAPORAN AKHIR INTERNATIONAL RESEARCH COLLABORATION AND SCIENTIFIC PUBLICATION

Transcription

1 LAPORAN AKHIR INTERNATIONAL RESEARCH COLLABORATION AND SCIENTIFIC PUBLICATION STUDY OF Fe-INDUCED MAGNETIC STATE IN ELECTRON-DOPED HIGH-T c SUPERCONDUCTING CUPRATES Eu 2-x Ce x Cu 1-y Fe y O 4 Tahun ke-1 dari rencana 2 tahun Ketua/Anggota Tim Dr. Risdiana, M. Eng. NIDN: Dr. Togar Saragi, M. Si. NIDN: Drs. Wahyu Alamsyah Somantri, MS. NIDN: Sesuai dengan Keputusan DP2M DIKTI tentang Penetapan Penerima Penelitian, Pengabdian kepada Masyarakat dan Program Kreativitas Mahasiswa Nomor : 0263/E5/2014 tanggal 24 Januari 2014 UNIVERSITAS PADJADJARAN OKTOBER 2014

2 FINAL REPORT INTERNATIONAL RESEARCH COLLABORATION AND SCIENTIFIC PUBLICATION STUDY OF Fe-INDUCED MAGNETIC STATE IN ELECTRON-DOPED HIGH-T c SUPERCONDUCTING CUPRATES Eu 2-x Ce x Cu 1-y Fe y O 4 First Year For Two Years Research Project RESEARCH TEAM Dr. Risdiana, M. Eng. NIDN: Dr. Togar Saragi, M. Si. NIDN: Drs. Wahyu Alamsyah Somantri, MS. NIDN: Sesuai dengan Keputusan DP2M DIKTI tentang Penetapan Penerima Penelitian, Pengabdian kepada Masyarakat dan Program Kreativitas Mahasiswa Nomor : 0263/E5/2014 tanggal 24 Januari 2014 UNIVERSITAS PADJADJARAN OCTOBER 2014

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4 SUMMARY Superconductor is a material that has zero electrical resistivity when they are cooled down to sufficiently low temperatures. Superconductor is a promising material for future applications especially for energy saving such as for superconductor cable without any energy loss of electric power transmission and high performance power storage devices. However, the mechanism describing the role of physical properties in superconductor is still far from being understood clearly. The main purpose of this proposal is to elucidate the hole-electron doping symmetry in the high-t c cuprates and to find the key phenomena for explaining the appearance of high-t c superconductivity. The studies of physical properties through the partially substitution of impurities for Cu in both systems are one of important ways to elucidate the electron-hole doping symmetry. Different with hole-doped superconductor, to our knowledge, however, no one has reported the effects of magnetic impurities Fe on the Cu-spin dynamics in the electron-doped cuprates so that clear conclusion of the relation between the dynamical stripe correlations and superconductivity in the electron-doped cuprates has not yet been obtained. Here, crystal growth and study the effect of partially substitution of magnetic impurity Fe for Cu to the magnetic properties in electron-doped superconducting cuprates of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+ - with x = 0.15 and y = 0, 0.005, 0.010, 0.020, 0.030, have been investigated in order to clarify electron-hole doping symmetry in high T c superconductors. Samples with various δ valus are prepared by solid state reaction method. XRD data show that all samples have high quality samples for δ valus in the range between The magnetic dcsusceptibility measurements show superconductivity with T c onset about 15 K and 10 K, respectively for y = 0 and T c decreases with decreasing Fe and disappear for y larger than 0.02 and It is indicating that impurity Fe successfully disturbing spin-spin correlation in Cu layer. Volume fraction of the superconducting state (V SC ) decreases markedly from 100 % to 30 % with only 0.5 % impurity substitution. V SC is completely zero when the concentration of Fe is larger than 2 %. From these results, it is found that partially substitution of magnetic impurity Fe for Cu effectively decreased superconducting properties of electron-doped superconductor Eu 2-x+y Ce x- ycu 1-y Fe y O 4+α-δ. Keywords: Electron-doped superconducting cuprates, Fe impurities, DC magneticsusceptibility. ii

5 PREFACE We would like to thanks to DIKTI, LPPM Universitas Padjadjaran, Dean of Faculty of Mathematics and Natural Sciences Universitas Padjadjaran, and head of Department of Physics Universitas Padjadjaran, who supported our research with title Study Of Fe-Induced Magnetic State In Electron-Doped High-T c Superconducting Cuprates Eu 2-x Ce x Cu 1-y Fe y O 4. These researches also based on research collaboration with Tohoku University and RIKEN, Japan and became one part of research theme in the road map of research collaboration on the basis scheme of MoU between four Universities (UNPAD, ITB, ITS, UGM) and RIKEN Nishina Center, Japan. We hope this project will give the opportunity for undergoing of undergraduate student to take final project related to this field. Jatinangor, October 28, 2014 Research team iii

6 CONTENT LEMBAR PENGESAHAN i SUMMARY ii PREFACE iii CONTENT iv LIST OF TABLE LIST OF FIGURE LIST OF APPENDIX CHAPTER I INTRODUCTION Background Objective Output 4 CHAPTER II LITERATURE STUDY 6 CHAPTER III RESEARCH OBJECTIVE AND ADVANTAGES 9 CHAPTER IV RESEARCH METODOLOGY 13 CHAVTER V RESULTS 13 CHAVTER VI RESEARCH PLANNING 13 CHAVTER VII CONCLUSSION REFFERENCES 14 APPENDIX 1 JUSTIFICATION OF RESEARCH BUDGET 16 APPENDIX 2 SUPPORTING FACILITIES 19 APPENDIX 3 RESEARCH TEAM AND CONTRIBUTIONS 20 APPENDIX 4 LETTER OF AGGREEMENT FOR RESEARCH 21 COLLABORATION APPENDIX 5 CURRICULUM VITAE 28 APPENDIX 6 SURAT PERNYATAAN KETUA PENELITI 43 iv

7 LIST OF TABLE Table 1. Table 2. Roadmap for exploration of new materials for energy applications on the basis scheme of MoU between UNPAD, ITB, ITS, UGM and RIKEN Nishina Center, Japan Annealing conditions and δ for various samples of Eu 2-x+y Ce x-y Cu 1- yfe y O 4+α-δ 5 14 v

8 LIST OF FIGURE Figure 1. Schematic phase diagram of the hole- and electron-doped cuprate. AF and SC indicate antiferromagnetic order and superconductivity, respectively. Figure 2 µzf- SR time spectra of hole-doped La 2-x Sr x Cu 0.97 Zn 0.03 O 4 with x 7 = at 0.3 K (Risdiana et al., 2008). Figure 3. Temperature dependence of the depolarization rate of the slowly 8 depolarizing component λ 0 for typical values of x in La 2 x Sr x Cu 1 y Fe y O 4 with y = 0.01 (Suzuki et al., 2012). Figure 4. Diagram Block for research methodology 11 Figure 5. Raw materials of powders after mixed 12 Figure 6. Samples after annealing at 860 o C (a) and 900 o C (b) for 13 hours 12 Figure 7. XRD pattern of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ with x = 0.15 and y = 0 at various δ values Figure 8. XRD pattern of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ with x = 0.15 and y = at various δ values Figure 9. XRD pattern of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ with x = 0.15 and y = 0.01 at various δ values Figure 10. XRD pattern of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ with x = 0.15 and y = 0.02 at various δ values Figure 11. XRD pattern of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ with x = 0.15 and y = 0.03 at various δ values Figure 12. XRD pattern of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ with x = 0.15 and y = 0.05 at various δ values Figure 13. Preparation of the powdered sample for DC magnetic-susceptibility measurements Figure 14. DC magnetic-susceptibility on zero-field cooling (ZFC) and field Figure 15. cooling (FC) for Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ with with x = 0.15 and y = 0, 0.005, 0.010, 0.020, and at various δ values. Fe concentration (y) dependence of superconductor volume fraction V SC for Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ vi

9 LIST OF APPENDIX APPENDIX 1 APPENDIX 2 APPENDIX 3 APPENDIX 4 APPENDIX 5 SUPPORTING FACILITIES RESEARCH TEAM AND CONTRIBUTIONS LIST OF PUBLICATION NUMBER OF INVOLVED STUDENTS FORMULIR EVALUASI ATAS CAPAIAN LUARAN KEGIATAN vi

10 CHAPTER I INTRODUCTION 1.1 Background Superconductor is a material that has zero electrical resistivity when they are cooled down to sufficiently low temperatures. Most of superconductors are cuprate compounds. One of their characteristics is that conducting planes of CuO 2 are included in their crystal structures and responsible for their electronic properties. When the CuO 2 plane loses one electron because of doping, one mobile hole remains in the CuO 2 planes, leading to the formation of a hole-doped superconducting cuprate. On the other hand, when the CuO 2 plane gets an excess electron, superconductivity realizes and forms an electron-doped superconducting cuprates. Superconductor is a promising material for future applications especially for energy saving such as for superconductor cable without any energy loss of electric power transmission and high performance power storage devices. However, the mechanism describing the role of physical properties in superconductor is still far from being understood clearly. The hole-electron doping symmetry in the high-t c cuprates has been one of central interests in relation to the mechanism of the high-t c superconductivity. In order to describe the mechanism of the high-t c superconductivity, a stripe model of spins and charges is suggested to be a probable one. Lots of studies have been carried out to clarify the relationship between stripes and superconductivity and the existence of stripe correlations of spins and charges have been established in hole-doped systems (Risdiana et al., 2008, Adachi et al., 2008). Especially, dynamically fluctuating stripes (dynamic stripes) have been theoretically suggested to play an important role for the appearance of superconductivity (Emery et.al., 1999). On the other hand, the stripe correlations have not yet been clearly observed in electron-doped systems even though the high-t c superconductivity actually appears in the systems. Thus, from the view point of the stripe model, the dynamic property of the electronic state of electron-doped systems is now recognized to be important to understand the role of stripes to the superconductivity. However, because of difficulties of sample preparations, the study of electron-doped systems has not been progressed so much and clear answer has not been achieved yet. We performed Zero Field muon spin relaxation (ZF- SR) in hole-doped cuprates La 2-x Sr x Cu 1-y Fe y O 4 (LSCFO), in order to investigate magnetic impurities 1

11 effect of Fe on the Cu-spin dynamics. it has been found that the magnetic transition temperature and magnetic correlation are enhanced through the 1% Fe substitution in a wide range of hole concentration where superconductivity appears in Fe-free La 2 x Sr x CuO 4. Therefore, partially Fe substitution in electron-doped cuprates is potential impurity to study the Cu-spin dynamics in the electron-doped system. To our knowledge, however, no one has reported the effects of magnetic impurities Fe on the Cu-spin dynamics in the electron-doped cuprates so that clear conclusion of the relation between the dynamical stripe correlations and superconductivity in the electron-doped cuprates has not yet been obtained. Here, we propose to growth high quality polycrystalline samples of electron-doped high-t c superconducting cuprates Eu 2-x Ce x Cu 1-y Fe y O 4 to understand Fe-induced magnetic state in electron-doped high-t c superconducting cuprates. An advantage of this sample rather than other types of electron-doped systems is that the absence of rare earth moments such as Pr 3+ moments in Pr 1-x LaCe x CuO 4. Using Eu 2-x Ce x CuO 4 samples, we can directly observe the dynamic behavior of Cu-spins and effects of impurity to them without any magnetic disturbance. Thus, this system would be a good candidate to achieve the answer to the objective of this proposed study. In any case, this proposed study will give us the important information of the mechanism of superconductivity based upon the dynamical stripe correlations in the high-t c superconducting cuprates. All samples of electron-doped high-t c superconducting cuprates Eu 2-x+y Ce x- ycu 1-y Fe y O 4 will be prepared in Padjadjaran University. On the other hand, in the first year, Tohoku University will support all magnetic characterizations such as susceptibility measurements using SQUID magnetometer (Quantum Design, Model MPMS-XL5), and in the second year, The Physical and Chemical Research Institute (RIKEN), Japan will support all muon spin relaxation measurements using SR spectroscopy in RIKEN-Rutherford Appleton Laboratory (RAL) muon facility at Oxford, UK. 1.2 Objective The main purpose of the proposed study is to elucidate whether the dynamic stripes are a key phenomena for the high-t c superconductor or not and whether the hole-electron doping symmetry is observed in the high-t c superconductor or not. We aim to clarify the dynamic property of magnetic state in electron-doped high-t c 2

12 superconducting cuprates. In order to investigate the dynamic property of stripes, a pinning effect by impurities is a good way to be studied. Here, we chose Eu 2-x+y Ce x-y Cu 1-y Fe y O 4 to understand Fe-induced magnetic state in electron-doped high-t c superconducting cuprates and to achieve the answer to the objective of this proposed study. 1.3 Ouput After finishing this research program, we will be able to prepare one international publication every year (two international publications in total for two year) and all the results will be presented in one international conference every year (twice international conferences in total for two years) based on research collaboration with Tohoku University and RIKEN, Japan. This research also become one part of research theme in the road map of research collaboration on the basis scheme of MoU between four Universities (UNPAD, ITB, ITS, UGM) and RIKEN Nishina Center, Japan as shown in Table 1. In addition, this research collaboration will give the opportunity for undergoing of undergraduate student to take final project related to this field. 3

13 Table 1. Roadmap for exploration of new materials for energy applications on the basis scheme of MoU between UNPAD, ITB, ITS, UGM and RIKEN Nishina Center, Japan. Short Term ( ) Medium Term ( ) Long Term ( ) Infrastructure and Facility Development Prototype Development Applied Research Fundamental Aspects Designs and fabrications of active working device models and the prototypes. Output : international publications and Patents Exploration and verification of novel functionalities of new materials and new structures Output : international publications The correlation between the structural properties and the functionalities in composite materials and organicinorganic compounds for energy applications (solar cell, thermoelectric and dissipation less power transmission). Output : international publications Prototype Performance Testing and Characterization Laboratory Physical Properties Measurement for energy efficiency Laboratory Sample Preparation Laboratory for composite materials, organicinorganic hybrids Laboratory. Physical Properties Measurement System Laboratory, Material Computation Laboratory 4

14 CHAPTER II LITERATURE STUDY Superconductor is a material showing a phenomenon that has zero electrical resistivity when they are cooled down to sufficiently low temperatures. The temperature at which the electrical resistivity starts to be zero is called the critical temperature (T c ). Because of this phenomenon, some applications are developed for future technology especially for energy saving such as for superconductor cable without any energy loss of electric power transmission and high performance power storage devices. Most of superconductors are cuprate compounds. These superconducting cuprates are often called high-t c superconducting cuprates (HTSC). The era of high- T c superconducting cuprates began when Bednorz and Muller reported possible superconductivity in single-layer cuprates called 214 cuprates (Bednorz et al., 1986). The parent compound of these cuprates is La 2 CuO 4. Superconductivity appears by randomly substituting some Sr atoms for La and forming La 2-x Sr x CuO 4. When a La 3+ ion is replaced by Sr 2+, the CuO 2 plane loses one electron so that one mobile hole remains in the CuO 2 planes, leading to the formation of a hole-doped cuprate. Another family of single-layer cuprates is the electron-doped (Nd, Pr, Sm)-Ce-Cu-O. In these materials, when a Nd 3+ or Pr 3+ or Sm 3+ is replaced by Ce 4+, the CuO 2 plane gets an excess electron, leading to the formation of an electron-doped cuprates (Tokura et al., 1989). All of the crystals have common structures consist of both the conduction layer (CuO 2 plane) and the charge reservoir layer. CuO 2 planes are responsible for their electronic properties. Electron-doped x S Figure 1. Schematic phase diagram of the hole- and electron-doped 214 cuprate. AF Electron doping Hole doping and SC indicate antiferromagnetic order and superconductivity, respectively. 5 T AF Hole-doped S

15 The so-called hole-electron doping symmetry in the high-t c cuprates has been one of central interests in relation to the mechanism of the high-t c superconductivity. Phase diagrams of the hole- and electron-doped systems are very similar to each other. That is, the parent compounds are both Mott insulators exhibiting long-range antiferromagnetic order with similar values of the Neel temperature. The superconducting phases appear through doping holes or electrons into the Mott insulators as shown in Fig 1. These properties lead to the view of hole-electron doping symmetry. On the other hand, some properties in the electron-doped superconductors have been found to be different from those in the hole-doped superconductors, leading to the hole-electron doping asymmetry. First, the effectiveness of carriers for destroying the long-range antiferromagnetic order is different between the hole- and electron-doped systems. In the electron-doped system of Nd 2-x Ce x CuO 4, the longrange antiferromagnetic order survives up to x ~ 0.13 (Takagi et al., 1989), while it survives only up to x ~ 0.02 in the hole-doped system of La 2-x Sr x CuO 4. Secondly, in the inelastic neutron-scattering measurements, an incommensurate spin-correlation, which may be due to the so-called dynamically fluctuating stripes of spins and holes (Tranquada et al., 1995), has been found in the hole-doped system (Yamada et al., 1998). In the electron-doped system, on the other hand, a commensurate spin-correlation, which is related to the simple antiferromagnetic order, has been observed (Yamada et al., 2003). Impurity-substitution effects to the some physical properties have been also intensively studied to understand the role and mechanism of superconductivity. Different behaviors between the hole- and electron-doped systems are also observed. For examples, the superconductivity in the electron-doped system is suppressed through the substitution of magnetic Ni for Cu more markedly than through the substitution of nonmagnetic Zn for Cu (Tarascon et al., 1990), which is contrary to the result in the hole-doped system (Xiao et al., 1990). From the view of the Cu-spin dynamics properties, one of important phenomena in the 214 cuprates is that in hole-doped system, charge in the CuO 2 plane are not distributed homogeneously but form quasi-one-dimensional charge stripes. The charge stripes are manifestation of a self-organized state. In 1995, Tranquada et al. suggested a stripe model of spins and holes from neutron scattering measurements to understand the mechanism of the 1/8 anomaly around p = 1/8 (Tranquada et al., 1995). That is, dynamically fluctuating stripes are pinned and stabilized by the 6

16 tetragonal low-temperature structure (space group: P4 2 /ncm), leading to the static stabilization and suppression of superconductivity at p = 1/8. These results can be well described using the stripe model. This model consists of hole (charge) domains and spin domains. Charge stripes refer to a charge density wave (CDW) and spin stripes refer to a spin density wave (SDW). From ZF- SR measurements, it has been found that a slight amount of Zn tends to induce slowing down of the Cu-spin fluctuations in the whole superconducting regime of hole-doped system, which is able to be interpreted as being due to pinning and stabilization of the dynamically fluctuating stripes of spins and holes (Risdiana et al., 2008, Adachi et al., 2008). Figure 2. ZF- SR time spectra of hole-doped La 2-x Sr x Cu 0.97 Zn 0.03 O 4 with x = at 0.3 K (Risdiana et al., 2008). Figure 2 shows the ZF- SR time spectra at 0.3 K for La 2-x Sr x Cu 0.97 Zn 0.03 O 4 with x = (Risdiana et al., 2008). The muon-spin depolarization becomes weak with increasing x but still shows an exponential-like depolarization at x = The exponential-like depolarization disappears at x = 0.30 where the superconductivity also disappears in the Zn-free y = 0. Therefore, these results suggest that the pinning of the dynamically fluctuating stripes occurs in the overdoped regime as well, that is, the stripe-pinning model holds good even for overdoped La 2-x Sr x CuO 4. This result might point to the importance of the dynamical stripe correlations in the appearance of high-t c superconductivity in the hole-doped system (Emery et al., 1999). For Fe substitution samples of La 2-x Sr x Cu 1-y Fe y O 4, it has been found that the magnetic transition temperature and magnetic correlation are enhanced through the 1% Fe substitution in a wide range of hole concentration where superconductivity appears in Fe-free La 2 x Sr x CuO 4 (Suzuki et al., 2012). 7

17 Figure 3. Temperature dependence of the depolarization rate of the slowly depolarizing component λ 0 for typical values of x in La 2 x Sr x Cu 1 y Fe y O 4 with y = 0.01 (Suzuki et al., 2012). Figure 3 show the temperature dependence of the depolarization rate of the slowly depolarizing component λ 0 for typical values of x in La 2 x Sr x Cu 1 y Fe y O 4 with y = 0.01 (Suzuki et al., 2012). It appears that two peaks of λ 0 observed in x = 0.16 originate from the stripe order of Cu spins at low temperatures below ~ 4 K and from the spin-glass state of Fe spins at temperatures below ~ 15 K. Therefore, it is guessed that the two magnetic state change with changing hole doping. In other hand, the mechanism of superconductivity in the electron-doped high- T c cuprates has not yet been clarified also. It is of great interest whether the stripepinning model holds good even for the electron-doped system or not and whether the mechanism in the electron-doped high- T c cuprates is different from that in the holedoped ones or not. We measured the ZF- SR time spectra of Pr 0.86 LaCe 0.14 Cu 1- yzn y O 4+ - with y = 0, 0.01, 0.02, 0.05 and large values (Risdiana et al., 2010). It is found that the spectra are independent of the Zn concentration, meaning that no impurity-induced slowing down of the Cu-spin fluctuations is detected in electrondoped Pr 0.86 LaCe 0.14 CuO That is, Zn impurities do not appear to affect the Cuspin dynamics, which is very different from the results of hole-doped La 2-x Sr x Cu 1- yzn y O 4 as shown in Fig. 2. This may be understood in two ways. First, there may be no dynamically fluctuating stripes of spins and electrons in the electron-doped cuprates, because the dynamical stripes lead to the impurity-induced magnetic order in the hole-doped cuprates (Adachi et al., 2004). Second, the effect of Pr 3+ moments may be too strong for the effect of a small amount of Zn impurities to be observed. To 8

18 be conclusive, another electron-doped cuprate without Pr 3+ moments such as Eu 2- xce x CuO 4 should be used for this study. An advantage of this sample rather than other types of electron-doped systems is that the absence of rare earth moments such as Pr 3+ moments in Pr 1-x LaCe x CuO 4. Using Eu 2-x Ce x CuO 4 samples, we can directly observe the dynamic behavior of Cu-spins and effects of impurity to them without any magnetic disturbance. Thus, this system would be a good candidate to achieve the answer to the objective of this proposed study. Due to the previous study of effect of Fe on the Cu-spin dynamics in holedoped system, partially Fe substitution in electron-doped cuprates is potential impurity to study the Cu-spin dynamics in the electron-doped system. Therefore, the study of spin dynamics in the electron-doped system and the following comparison with the results of the hole-doped system will lead to an understanding of the general mechanism of the superconductivity. 9

19 CHAPTER III RESEARCH OBJECTIVE AND ADVANTAGES 3.1 Objective The main purpose of this research is to elucidate whether the dynamic stripes are a key phenomena for the high-t c superconductor or not and whether the holeelectron doping symmetry is observed in the high-t c superconductor or not. We aim to clarify the dynamic property of magnetic state in electron-doped high-t c superconducting cuprates. In order to investigate the dynamic property of stripes, a pinning effect by impurities is a good way to be studied. Here, we chose Eu 2-x+y Ce x- ycu 1-y Fe y O 4 to understand Fe-induced magnetic state in electron-doped high-t c superconducting cuprates and to achieve the answer to the objective of this research. 3.2 Advantages The advantages of this research are listed below. a. These studies will be useful for comparison with our previous study in electrondoped Pr 1-x LaCe x Cu 1-y Zn y O 4 and hole-doped La 2-x Sr x Cu 1-y Fe y O 4 to find the key phenomena for explaining the appearance of high-t c superconductivity in the point of view spin dynamics properties. b. Understanding the physical theory about phenomena for the high-t c superconductor especially about the hole-electron doping symmetry. c. After finishing this research program, we will be able to prepare one international publication every year (two international publications in total for two year) d. This research collaboration will give the opportunity for undergoing of undergraduate student to take final project related to this field. 10

20 CHAPTER IV RESEARCH METHODOLOGY The method of our research is experimental research described in Figure 4. Samples Preparations Mixed Eu 2 O 3, CeO 2, CuO, Fe 2 O 3 Prefire 900 o C, 20 h Reground and press Magnetic properties measurements X-Ray Diffraction Susceptibility Sinter 1100 o C, 16 h Anneal 950 o C, 10 h Figure 4. Diagram Block for research methodology Figure 4 shows the research methodology of our proposal. First part is samples preparations. Polycrystalline samples of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4 (ECCFO) with x = 0.15 and y = 0, 0.005, 0.01, 0.02, 0.03 and 0.05 were prepared by the ordinary solidstate reaction method as follows. From April to July 2014, we prepared Polycrystalline samples of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4 (ECCFO) with x = 0.15 and y = 0, 0.005, and Raw materials of Eu 2 O 3, CeO 2, CuO and Fe 2 O 3 powders were mixed in a stoichiometric ratio and prefired in air at 900 o C for 20 h. The prefired materials are reground and pressed into pellets of 10 mm in diameter, and sintered in air at 1000 o C for 16 h with repeated regrinding. As-grown samples of ECCFO, are annealed in flowing Ar gas of high purity (6N) at various temperature between 950 o C for 10 h in order to remove the excess oxygen at the apical site. All samples preparations will be doing in Unpad. Second part is checking quality and measuring magnetic properties of the samples such as XRD, resistivity and DC magnetic-susceptibility measurements that carried out at low temperatures down to 2 K using a standard SQUID magnetometer (Quantum Design, Model MPMS-XL5) in a magnetic field of 5 Oe on field cooling. All the second parts have been doing in Koike Laboratory at Tohoku University and at the Rutherford-Appleton Laboratory in the UK. 11

21 CHAPTER V RESULTS 5.1 Crystal Growth Polycrystalline samples of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4 with x = 0.15 and y = 0, 0.005, 0.010, 0.020, and were prepared by the ordinary solid-state reaction method. Raw materials of powders were mixed in a stoichiometric ratio and prefired in air at 900 o C for 20 h. Figure 5 shows raw materials of powders after mixed in stoichiometric ratio. The grey color of raw materials after mixed is observed. Figure 5. Raw materials of powders after mixed The prefired materials are reground and pressed into pellets of 10 mm in diameter, and sintered in air at 1000 o C for 16 h with repeated regrinding. The samples after sintering are called As-grown samples of ECCFO. As-grown samples of ECCFO are annealed in flowing Ar gas of high purity (6N) at various temperatures in between 820 to 930 o C for 8 to 20 h in order to remove the excess oxygen at the apical site. The reduced oxygen content δ was estimated from the weight change before and after annealing. Figure 6 shows samples after annealing at 860 o C (a) and 900 o C (b) for 13 hours. (a) (b) Figure 6.Samples after annealing at 860 o C (a) and 900 o C (b) for 13 hours 12

22 Table 2 shows the summary of annealing conditions and delta (δ) after calculated using equations. The values of δ are varying between and The annealing processes can be reduced oxygen contents. However, the value of δ cannot be controlled well. Table 2. Annealing conditions and δ for various samples of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ No Composition Annealing Condition (g) (g) Temperature ( o C) Time (h) 1 y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y =

23 No Composition Annealing Condition (g) (g) Temperature ( o C) Time (h) 31 y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = y = Samples with δ values larger than 0.09 have a color changed in their surfaces. We believe it is because over-heated or over-reduced of oxygen content. Over-reduced oxygen content made de-composed the material in samples. The red color of surface after over-reduced annealing process is believed to be coming from Cu. 14

24 Intensity (arb. units) Intensity (arb. units) 5.2 XRD Measurement All of the samples were characterized through the powder X-ray diffraction (XRD) using X-Ray Bruker D8 Advance. Figure 7 shows XRD pattern of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ with x = 0.15 and y = 0 at various δ values. All main peaks of ECCO are shown in the spectra indicating high qualities of samples are formed for δ values smaller than For δ values larger than 0.09, some impurities peaks are observed due to decomposition of samples because of over-reduction of oxygen. (a) Eu 1.85 Ce 0.15 CuO 4+ As-grown (a) Eu 1.85 Ce 0.15 CuO 4+ As-grown (b) Eu 1.85 Ce 0.15 CuO 4+ = (f) Eu 1.85 Ce 0.15 CuO 4+ = (c) Eu 1.85 Ce 0.15 CuO 4+ = (f) Eu 1.85 Ce 0.15 CuO 4+ = (d) Eu 1.85 Ce 0.15 CuO 4+ = (g) Eu 1.85 Ce 0.15 CuO 4+ = (e) Eu 1.85 Ce 0.15 CuO 4+ = (g) Eu 1.85 Ce 0.15 CuO 4+ = Figure 7. XRD pattern of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ with x = 0.15 and y = 0 at various δ values Figure 8 shows XRD pattern of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ with x = 0.15 and y = at various δ values. There is no unexpected peak in all spectra indicating high qualities of samples in the range 15

25 Intensitas (arb Unit) Eu Ce Cu Fe O 4+ As Grown = 0 0 = H 0 = H 0 = H (degree) Figure 8. XRD pattern of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ with x = 0.15 and y = at various δ values Figures 9, 10, 11, 12 show pattern of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ with x = 0.15 and y = 0.01, 0.02, 0.03 and 0.05 at various δ values, respectively. Generally, with increasing Fe concentration, unexpected peaks are observed even in the lower δ values below We assumed that substitution of Fe affected to the de-composition of samples during oxygen reduction. 16

26 Intensitas (arb Unit) Intentsitas (arb Unit) Eu 1.86 Ce 0.14 Cu 0.99 Fe 0.01 O 4+ = H 0 = H 0 = H 0 = H (degree) Figure 9. XRD pattern of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ with x = 0.15 and y = 0.01 at various δ values Eu 1.87 Ce 0.13 Cu 0.98 Fe 0.02 O 4+ As Grown = 0 0 = H (degree) Figure 10. XRD pattern of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ with x = 0.15 and y = 0.02 at various δ values 17

27 Intensitas (arb. Unit) Intensitas (arb. Unit) Eu 1.88 Ce 0.12 Cu 0.98 Fe 0.03 O 4+ As Grown = 0 0 = H 0 = H (degree) Figure 11. XRD pattern of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ with x = 0.15 and y = 0.03 at various δ values Eu 1.9 Ce 0.1 Cu 0.95 Fe 0.05 O 4+ As Grown = 0 0 = H 0 = H 0 = H Figure 12. XRD pattern of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ with x = 0.15 and y = 0.05 at various δ values 18 2 (degree)

28 (10-4 emu/gr) 5.3 DC Magnetic-Susceptibility DC magnetic-susceptibility measurements were carried out at low temperatures down to 2 K using a standard SQUID magnetometer (Quantum Design, Model MPMS-XL5) in a magnetic field of 5 Oe on field cooling. A sintered pellet of the polycrystalline sample was pulverized to be powdered. The powdered sample with mg in weight was covered with parafilm and inserted into a plastic tube as shown in Figure 13. Figure 13. Preparation of the powdered sample for DC magnetic-susceptibility measurements Eu 1,85+y Ce 0.15-y Cu 1-y Fe y O H = 5 Oe T (K) Figure 14. DC magnetic-susceptibility on zero-field cooling (ZFC) and field cooling (FC) for Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ with with x = 0.15 and y = 0, 0.005, 0.010, 0.020, and at various δ values. y = 0, = y = 0.005, = y = 0.010, = y = 0.020, = y = 0.030, = y = 0.050, =

29 V SC (%) Figure 14 shows temperature dependence of dc magnetic-susceptibility on field cooling at 5 Oe for Eu 1.85+y Ce 0.15-y Cu 1-y Fe y O 4+ - with y = and values from to For impurity-free samples of y = 0, diamagnetic behavior with smaller than 0 is observed starting from about 15 K. This temperature can be defined as T c onset for this sample. For y = 0.005, T c onset decreases to be around 10 K. The trace of superconductivity disappeared at y It is indicating that impurity Fe successfully disturbing spin-spin correlation in Cu layer in electron-doped superconducting cuprates. The volume fraction of the superconducting state, V SC, has been estimated from the absolute value of at 2 K. The value of at 2 K of impurity-free samples is assumed as correspond to 100 % of V SC. The value of V SC for each impuritysubstituted sample is estimated using equation below :. χ ECCO is the value of at 2 K for impurity-free samples, χ ECCFO is the value of at 2 K for Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ Eu 1,85+y Ce 0.15-y Cu 1-y Fe y O Figure 15. Fe concentration (y) dependence of superconductor volume fraction V SC for Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ. y 20

30 Figure 15 shows Fe concentration (y) dependence of volume fraction of the superconducting state (V SC ). It is found that V SC decreases markedly from 100 % to 30 % with only 0.5 % impurity substitution. V SC is completely zero when the concentration of Fe is larger than 2 %. From these results, it is found that partially substitution of magnetic impurity Fe for Cu effectively decreased superconducting properties of electron-doped superconductor Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ. 21

31 CHAPTER VI RESEARCH PLANNING In the second year, crystal growth with optimization growth condition, XRD and µsr measurements will be performed. 6.1 Crystal Growth Polycrystalline samples of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4 (ECCFO) with x = 0.15 and y = 0, 0.005, 0.01, 0.02, 0.03 and 0.05 will be completely prepared by the ordinary solidstate reaction method. Annealing condition will be optimized to get high quality samples with best δ values in between 0.03 and For these purposes, variation of temperatures and times will be needed. The annealing will be performed in Ar gas flow with temperature between 850 o C and 830 o C for 14, 12 and 10 h. 6.2 XRD Measurements All of the samples after annealing will be characterized by the powder X-ray diffraction (XRD) at Tohoku University. 6.3 µsr measurements After checking quality and crystal structure of all annealed samples, µsr measurements will be performed to understand the effect of magnetic impurity Fe to the Cu-spin dynamics in electron-doped superconductor ECCFO. Muon spin relaxation (µsr) technique is a very sensitive method for detecting internal magnetic fields due to ordered magnetic moments or random magnetic fields that are static or fluctuating with time. A positive muon is an unstable particle with the spin quantum number S = 1/2 and the life time is only about two millionths of a second. As a muon stops around an interstitial site and makes precession under a local magnetic field, it is employed as a pointlike probe of the local magnetic environment around the interstitial site at which it stops. When the muon spontaneously decays into a positron and a neutrino-anti-neutrino pair, the positron is emitted to the direction along which the spin of the muon was oriented. Positrons are detected by two opposing counters (forward (F) and backward (B) directions). Using the numbers of positrons detected by the forward and backward counters, F(t) and B(t), the asymmetry, A(t), is then defined. For µsr measurements, 4 or 5 samples in pellet with diameter of 10 mm 22

32 were used. Using apiezon N grease, the samples were set on Ag plate attached to the cryostat. The measurements above 2 K were performed at the RIKEN-RAL muon facility in the UK. The proposal to perform µsr at RIKEN-RAL muon facility has been approved. 23

33 CHAPTER VII CONCLUSION Eelectron-doped high-t c superconducting cuprates of Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ (ECCFO) with x = 0.15 and y = 0, 0.005, 0.01, 0.02, 0.03 and 0.05 have been prepared in order to investigate the effects of Fe impurities to the magnetic properties in the electron-doped system. Various annealing conditions resulted samples with δ values varying between and All of XRD data show that all samples have high quality when the sample has δ values smaller than that of DC magneticsusceptibility measurements of samples with x = 0.15, y = 0, show superconductivity with T c onset about 15 K and 10 K, respectively. The trace of superconductivity disappeared at y It is indicating that impurity Fe successfully disturbing spin-spin correlation in Cu layer in electron-doped superconducting cuprates. Volume fraction of the superconducting state (V SC ) decreases markedly from 100 % to 30 % with only 0.5 % impurity substitution. V SC is completely zero when the concentration of Fe is larger than 2 %. From these results, it is found that partially substitution of magnetic impurity Fe for Cu effectively decreased superconducting properties of electron-doped superconductor Eu 2-x+y Ce x-y Cu 1-y Fe y O 4+α-δ. 24

34 REFFERENCES (Adachi et al., 2008) T. Adachi, N. Oki, Risdiana, S. Yairi, Y. Koike, I. Watanabe, 2008, Effect of Zn and Ni substitution on the Cu-spin dynamics and superconductivity in La 2-x Sr x Cu 1-y (Zn,Ni) y O 4 (x = ): muon spin relaxation and magnetic susceptibility study, Phys. Rev. B 78, (Adachi et al.,2004) T. Adachi, S. Yairi, K. Takahashi, Y. Koike, I. Watanabe, K. Nagamine, 2004, Muon spin relaxation and magnetic susceptibility studies of the effects of nonmagnetic impurities on the Cu spin dynamics and superconductivity in La 2-x Sr x Cu 1-y Zn y O 4 with x = 0.115, Phys. Rev. B 69, (Bednorz et al., 1986) J. G. Bednorz and K. A. Muller, 1986, Possible hight c superconductivity in the Ba La Cu O system, Phys. B 64, 189. (Emery et.al., 1999) V. J. Emery, S. A. Kivelson, J. M. Tranquada, 1999, Stripe phases in high-temperature superconductors, Proc. Natl. Acad. Sci. 96, (Koike et al., 1992) Y. Koike, A. Kakimoto, M. Mochida, H. Sato, T. Noji, M. Kato and Y. Saito, 1992, Superconductivity and Electrical Resistivity in the T -Phase Pr 2-y La y-x Ce x CuO 4-δ, Jpn. : J. Appl. Phys. 31, (Risdiana et al., 2010) Risdiana, T. Adachi, N. Oki, Y. Koike, T. Suzuki, I. Watanabe, 2010, Muon-spin-relaxation study of the Cuspin dynamics in electron-doped high-t c superconductor Pr 0.86 LaCe 0.14 Cu 1-y Zn y O 4, Physical Review B 82, (Risdiana et al., 2008) Risdiana, T. Adachi, N. Oki, S. Yairi, Y. Tanabe, K. Omori, T. Suzuki, I. Watanabe, A. Koda, W. Higemoto and Y. Koike, 2008, Cu-spin dynamics in overdoped regime of La 2-x Sr x Cu 1-y Zn y O 4 probed by muon spin relaxation, Phys. Rev. B 77, (Risdiana et al., 2005) Risdiana, T. Adachi, Y. Koike, I. Watanabe and K. 25

35 Nagamine, 2005, Absence of the impurity-induced magnetic order in the electron-doped high-t c cuprates Pr o.86 LaCe 0.14 Cu 1-y (Zn,Ni) y O 4, Physica C , 355. (Suzuki et al., 2012) K. M. Suzuki, T. Adachi, Y. Tanabe, H. Sato, Risdiana, Y. Ishii, T. Suzuki, I. Watanabe, Y. Koike, 2012, Distinct Feinduced magnetic states in the underdoped and overdoped regimes of La 2-x Sr x Cu 1-y Fe y O 4 revealed by muon spin relaxation, Physical Review B 86, (Takagi et al., 1989) H. Takagi, S. Uchida, Y. Tokura, 1989, Superconductivity produced by electron doping in CuO 2 -layered compounds, Phys. Rev. Lett 62, (Tarascon et al., 1990) J. M. Tarascon, E. Wang, S. Kievelson, B. G. Bagley, G. W. Hull, R. Ramesh, 1990, Magnetic versus nonmagnetic ion substitution effects on T c in the La-Sr-Cu-O and Nd-Ce-Cu- O systems, Phys. Rev. B 42, 218. (Tokura et al., 1989) Y. Tokura, H. Takagi, S. Uchida, 1989, A superconducting copper oxide compound with electrons as the charge carriers, Nature 337, 345. (Tranquada et al., 1995) J. M. Tranquada, B. J. Sternlieb, J. D. Axe, Y. Nakamura, S. Uchida, 1995, Evidence for stripe correlations of spins and holes in copper oxide superconductors, Nature 375, 561. (Xiao et al., 1990) G. Xiao, M. Z. Cieplak, J. Q. Xiao, C. L. Chien, 1990, Magnetic pair-breaking effects: Moment formation and critical doping level in superconducting La 1.85 Sr 0.15 Cu 1-x A x O 4 systems (A=Fe,Co,Ni,Zn,Ga,Al), Phys. Rev. B 42, (Yamada et al., 2003) K. Yamada, K. Kurahashi, T. Uefuji, M. Fujita, S. Park, S. H. Lee, Y. Endoh, 2003, Commensurate Spin Dynamics in the Superconducting State of an Electron-Doped Cuprate Superconductor, Phys. Rev. Lett 90, (Yamada et al., 1998) K. Yamada, C. H. Lee, K. Kurahashi, 1998, Doping dependence of the spatially modulated dynamical spin correlations and the superconducting-transition temperature in La 2-x Sr x CuO 4, Phys. Rev. B 57,

36 APPENDIX 1 SUPPORTING FACILITIES All samples of electron-doped high-t c superconducting cuprates Eu 2- xce x Cu 1-y Fe y O 4 will be prepared in Padjadjaran University. We have two furnaces that needed for growing high-t c superconducting cuprates. Tohoku University will support all magnetic characterizations such as susceptibility measurements using SQUID magnetometer (Quantum Design, Model MPMS- XL5), and The Physical and Chemical Research Institute (RIKEN), Japan will support all muon spin relaxation measurements using SR spectroscopy in RIKEN-Rutherford Appleton Laboratory (RAL) muon facility at Oxford, UK. Furnace (UNPAD) XRD D8 ADVANCE Bruker (Tohoku Univ) 27

37 RESEARCH TEAM AND CONTRIBUTIONS No Name/NIDN Institution 1 Dr. Risdiana, M. Eng. UNPAD / Dr. Togar Saragi, M.Si. UNPAD / Drs. Wahyu Alamsyah UNPAD Sumantri,MS / Research Field Material Science Material Science Material Science Research Period Contributions (hours/week) 15 Research designing, Crystal growth, results analysis, report 13 Crystal growth, Characterization, results analysis, report 13 Crystal growth, Characterization, results analysis, report 28

38 SUPPORTING FACILITIES RESEARCH TEAM AND CONTRIBUTIONS LIST OF PUBLICATION NUMBER OF INVOLVED STUDENTS FORMULIR EVALUASI ATAS CAPAIAN LUARAN KEGIATAN 29