NEW ROUTES TO MULTIFERROICS

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1 NEW ROUTES TO MULTIFERROICS C. N. R. RAO Jawaharlal Nehru Centre for Advanced Scientific Research & Indian Institute of Science Bangalore, India 1

2 MULTIFERROICS Ferromagnetic Ferroelectric Ferroelastic Spontaneous magnetization - applied magnetic field Spontaneous polarization - applied electric field Spontaneous deformation - applied stress 2

MAGNETOELECTRICS MAGNETOELECTRICS Magnetoelectrics

field on the polarization (magnetization)) of a

3 MAGNETOELECTRICS MAGNETOELECTRICS Magnetoelectrics are simultaneously ferromagnetic and ferroelectric and have coupling between them. It describes the influence of a magnetic (electric) field on the polarization (magnetization)) of a material. W. Eerenstein, N. D. Mathur & J. F. Scott, Nature, 442, 759 (2006) 3

4 Why are there so few magnetic ferroelectrics? Symmetry Electrical properties Chemistry of d 0 -ness Size of the small cation Structural distortion Magnetism vs d-orbital occupancy 4

FERROMAGNETISM A ferromagnetic material is one that undergoes a phase transition from a high temp phase that does not have a macroscopic magnetic moment to a low temp phase that has a spontaneous

5 FERROMAGNETISM A ferromagnetic material is one that undergoes a phase transition from a high temp phase that does not have a macroscopic magnetic moment to a low temp phase that has a spontaneous magnetization even in the absence of an applied magnetic field. ferromagnetic materials exhibit spontaneous magnetization on the application of magnetic field and it can be switched by an applied field. Ferromagnetic materials have two stable states (basis of memory application) 5

6 FERROELECTRICITY P E Z Ferroelectric materials exhibit spontaneous polarization with applied electrical field and it can be switched by an applied field. A B O 6

7 Old example: Ni 3 B 7 O13 I Piezoelectric - AFM from 64 K to ~120 K, and Ferroelectric WFM below 64 K 15kV/cm 30kV/cm Ferroelectric hysteresis loops (200 Hz) Quadratic magnetoelectric hysteresis loop E. Ascher et. al., J. Appl. Phys. 37, 1404 (1966) 7

8 Alternative routes for Multiferroics Tilting of polyhedra - YMnO 3 Spiral magnetic ordering - TbMnO 3 Frustrated magnetism - LnMn 2 O 5 (Ln = rare earth) Lone pair effect - BiAO 3 (A = Cr, Mn,, Fe) Local non-centrosymmetry - LnCrO 3 Charge-ordering LnFe 2 O 4, Ln 1-x A x MnO 3 (A = Ca, Sr, Ba) C N R Rao and C R Serrao, J. Mater. Chem. 17, 4931 (2007) 8

9 Alternative routes for Multiferroics Tilting of polyhedra - YMnO 3 Spiral magnetic ordering - TbMnO 3 Frustrated magnetism - LnMn 2 O 5 (Ln = rare earth) Lone pair effect - BiAO 3 (A = Cr, Mn,, Fe) Local non-centrosymmetry - LnCrO 3 Charge-ordering LnFe 2 O 4, Ln 1-x A x MnO 3 (A = Ca, Sr, Ba) C N R Rao and C R Serrao, J. Mater. Chem. 17, 4931 (2007) 9

by electrostatic and size effects buckling of the MnO

10 YMnO 3 Antiferromagnetic T N = 80 K Ferroelectric T C = 914 K Ferroelectricity in YMnO 3 is entirely driven by electrostatic and size effects buckling of the MnO 5 polyhedra M. Fiebig et.al. Nature, 419, 818 (2002) 10

11 YMnO 3 Measurements of ε and tan δ near T N ~ 80 K shows coupling between the ferroelectric and antiferromagnetic orders exist. Z. J. Huang et. al. Phys. Rev. B, 56, 2623 (1997) 11

12 LuMnO 3 LuMnO 3 is an CAFM with TN = 90 K Frequency dispersion of Dielectric constant in LuMnO 3 The anomaly in dielectric constant plot at the Néel temperature (90 K) is a evidence for coupling between magnetic and dipole moments. Ghosh, Sahu, Bhat and Rao (2008) 12

13 LuMnO 3 Raman Spectra of LuMnO 3 at different temperatures. Ghosh, Sahu, Bhat and Rao (2008) 13

14 LuMnO 3 Temperature- variation of the phonon frequencies 691 Raman Shift(cm -1 ) cm cm cm -1 Raman Shift (cm -1 ) cm cm cm cm cm Tem perature(k ) Temperature(K) Ghosh, Sahu, Bhat and Rao (2008) 14

15 InMnO 3 (a) M (μ B /f.u.) FC ZFC M (μ B /f.u.) 0.3 T = 10 K T = 300 K H (koe) -0.3 Dielectric constant (ε r ) (b) bulk 10k Hz 20k hz 30k Hz 40k Hz 50k Hz thin film T(K) T (K) InMnO 3 is an CAFM with T N = 50 K and ferroelectric with T CE 500 K Serrao, Kundu, Bhattacharjee, Krupanidhi, Waghmare and Rao. J. Appl. Phys. 100, (2006) 15

16 Alternative routes for Multiferroics Tilting of polyhedra - YMnO 3 Spiral magnetic ordering - TbMnO 3 Frustrated magnetism - LnMn 2 O 5 (Ln = rare earth) Lone pair effect - BiAO 3 (A = Cr, Mn,, Fe) Local non-centrosymmetry - LnCrO 3 Charge-ordering LnFe 2 O 4, Ln 1-x A x MnO 3 (A = Ca, Sr, Ba) C N R Rao and C R Serrao, J. Mater. Chem. 17, 4931 (2007) 16

17 TbMnO 3 TbMnO 3 has an orthorhombically distorted perovskite structure (space group Pbnm) Orange arrows denote Mn magnetic moments below T N T. Kimura et. al. Nature, 426, 55, (2003) 17

18 TbMnO 3 Temperature profiles of magnetization and sp. heat, dielectric constant and polarization Magnetic field induced change in the dielectric constant T. Kimura et. al. Nature, 426, 55 (2003) 18

19 Alternative routes for Multiferroics Tilting of polyhedra - YMnO 3 Spiral magnetic ordering - TbMnO 3 Frustrated magnetism - LnMn 2 O 5 (Ln = rare earth) Lone pair effect - BiAO 3 (A = Cr, Mn,, Fe) Local non-centrosymmetry - LnCrO 3 Charge-ordering LnFe 2 O 4, Ln 1-x A x MnO 3 (A = Ca, Sr, Ba) C N R Rao and C R Serrao, J. Mater. Chem. 17, 4931 (2007) 19

20 RMn 2 O 5 20

21 RMn 2 O 5 Magnetic and ferroelectric phase diagram of RMn 2 O 5 R = Sm Ho,Y as a function of the ionic radius of R (r( R ) M. Tachibana et. al. Phys. Rev. B, 72, , (2005) 21

22 TbMn 2 O 5 Temperature dependence of magnetic susceptibility along three crystallographic directions (2 koe) The temperature derivative of the magnetic susceptibility and specific heat Dielectric constant versus temperature (at 1 khz) N. Hur et. al., Nature, 429, 392, (2004) 22

23 TbMn 2 O 5 Temperature dependence of 1 khz dielectric constants Total electric polarization in various magnetic fields, measured after cooling in a magnetic field Total electric polarization along the b axis in magnetic fields. (Polarization is calculated by integrating measured pyroelectric current) Total electric polarization measured in zero magnetic field after cooling under different conditions N.Hur Hur et. et. al., al., Nature, 429, 392, (2004) 23

polarization by applied magnetic fields at 3 and 28 K (c) Polarization flipping at 3

24 TbMn 2 O 5 Reproducible polarization reversal by magnetic fields (a) Dielectric constant versus applied magnetic field at 3 and 28 K (b) Change of total electric polarization by applied magnetic fields at 3 and 28 K (c) Polarization flipping at 3 K by linearly varying magnetic field from 0 to 2 T N. Hur et. al., Nature, 429, 392, (2004) 24

25 TbMn 2 O 5, DyMn 2 O 5 TbMn 2 O 5 DyMn 2 O 5 J. Okamoto et. al., Phys. Rev. Lett., 98, , (2007) D. Higashiyama et. al., Phys. Rev. B., 70, , (2004) 25

26 Alternative routes for Multiferroics Tilting of polyhedra - YMnO 3 Spiral magnetic ordering - TbMnO 3 Frustrated magnetism - LnMn 2 O 5 (Ln = rare earth) Lone pair effect - BiAO 3 (A = Cr, Mn,, Fe) Local non-centrosymmetry - LnCrO 3 Charge-ordering LnFe 2 O 4, Ln 1-x A x MnO 3 (A = Ca, Sr, Ba) C N R Rao and C R Serrao, J. Mater. Chem. 17, 4931 (2007) 26

27 BiFeO 3 Weak magnetism at RT due to canted spin structure BiFeO 3 is ferroelectric below T CE ~ 1103 K and antiferromagnetic below T N ~ 643 K J. Wang et. al., Science, 299, 1719, (2003) 27

28 Role of Bi 6s lone pairs in BiMnO 3 First principles calculations indicate that the lone pair on the Bi ion in BiMnO 3 is stereochemically active and is the primary driving force behind the highly distorted low temperature monoclinic structure observed in this material. The occurrence of ferroelectricity is likely in BiMnO 3, and, if confirmed experimentally, will be a consequence of the Bi lone pair R. Sheshadri and N. A. Hill, Chem. Mater. 13, 2892 (2001) 28

29 BiMnO 3 BiMnO 3 is ferromagnetic (T C = 450 K) and ferroelectric (T CE = 105 K) Santos, Cheetham, Atou, Syono, Yamaguchi, Ohoyama, Chiba and Rao, Phys. Rev. B (2002) Santos, Parashar, Raju, Zhao, Cheetham & Rao, Solid State Commun. (2002) Kimura, Kawamoto, Yamada, Azuma, Takano & Tokura, Phys. Rev B (2003) 29

30 Problem with BiMnO 3! 1.Centrosymmetric space-group C2/c (theory + experiment) 2.Low polarization value 3.Is BiMnO 3 ferroelectric at all? 4.Impurities in samples prepared by high pressure 30

31 Three phases of BiMnO 3 with different ferroic properties BiMnO Intensity (a. u) 0 3x10 4 2x10 4 1x BiMnO 2.89 BiMnO 2.84 X-ray diffraction patterns of bismuth manganate showing three different phases θ (degree) Sundaresan, Mangalam, Iyo, Tanaka and Rao J. Mater. Chem. 18, 2191 (2008) 31

32 Magnetic measurements χ (emu/mol) BiMnO Oe FC BiMnO 2.89 BiMnO 2.84 M (μ B /Mn ion) M (μ B /Mn ion) M (μ B /Mn ion) H (koe) Temperature (K) H (koe) T = 5 K H (koe) T = 5 K T = 5 K Sundaresan, Mangalam, Iyo, Tanaka and Rao J. Mater. Chem. 18, 2191 (2008) 32

33 Dielectric measurements 1.0x x x x x Hz 500 Hz 1 khz 5 khz 10 khz 1 MHz BiMnO 2.99 ε r ' x x10 5 BiMnO x x Temperature (K) Sundaresan, Mangalam, Iyo, Tanaka and Rao J. Mater. Chem. 18, 2191 (2008) 33

34 BiMnO 3 Local Structure Results of Kodama et. al C2 (P2 1 or P2) From PDF (Just out) 34

35 Alternative routes for Multiferroics Tilting of polyhedra - YMnO 3 Spiral magnetic ordering - TbMnO 3 Frustrated magnetism - LnMn 2 O 5 (Ln = rare earth) Lone pair effect - BiAO 3 (A = Cr, Mn,, Fe) Local non-centrosymmetry - LnCrO 3 Charge-ordering LnFe 2 O 4, Ln 1-x A x MnO 3 (A = Ca, Sr, Ba) C N R Rao and C R Serrao, J. Mater. Chem. 17, 4931 (2007) 35

36 YCrO 3 : A New Multiferroic M (μ B / f.u.) H = 100 Oe M (μ B / f.u.) T = 5 K T = 120 K T = 200 K H (koe) T(K) YCrO 3 is an CAFM below 140 K and ferroelectric below 473 K Dielectric Constant (ε r ) Dielectric Constant (ε r ) Serrao, Kundu, Krupanidhi, Waghmare and Rao, Phys. Rev. B, 72, R220201, (2005) bulk 7500 thin film 200Hz 500Hz 1kHz 5kHz 10kHz T (K) 500Hz 200Hz T (K) 5kHz 500Hz 500Hz 1kHz 2kHz 3kHz 4kHz 5kHz 5kHz 10kHz Dissipation factor (D)

37 Local non-centrosymmetry! Ramesha, Llobet, Profen, Serrao and. Rao, J. Phys: Cond. Matt. 19, (2007) 37

38 Ramesha, Llobet, Profen, Serrao and. Rao, J. Phys: Cond. Matt. 19, (2007) 38

39 Ramesha, Llobet, Profen, Serrao and. Rao, J. Phys: Cond. Matt. 19, (2007) 39

40 Magnetic measurements Sahu, Serrao, Ray, Waghmare and Rao, J. Mater. Chem. 17, 42 (2007) 40

41 Dielectric phase transition Sahu, Serrao, Ray, Waghmare and Rao, J. Mater. Chem. 17, 42 (2007) 41

42 Rare Earth Chromites Lu Yb PM, PE Er Ho Y T (K) PM, FE Er Ho Y Lu Yb 100 CAFM, FE r R 3+ (Å) Sahu, Serrao, Ray, Waghmare and Rao, J. Mater. Chem. 17, 42 (2007) 42

43 Rare Earth Chromites SHG Measurements Quartz 1.00 YCrO LuCrO They are definitely ferroelectric. Therefore they are MULTIFERROIC 43

44 Alternative routes for Multiferroics Tilting of polyhedra - YMnO 3 Spiral magnetic ordering - TbMnO 3 Lone pair effect - BiAO 3 (A = Cr, Mn,, Fe) Frustrated magnetism - LnMn 2 O 5 (Ln = rare earth) Local non-centrosymmetry - LnCrO 3 Charge-ordering LnFe 2 O 4, Ln 1-x A x MnO 3 (A = Ca, Sr, Ba) C N R Rao and C R Serrao, J. Mater. Chem. 17, 4931 (2007) 44

45 LnFe 2 O 4 Dielectric dispersion in LuFe 2 O 4 Magnetocapacitance effect in LuFe 2 O 4 N. Ikeda et. al. Nature 436, 1136 (2005) M. A. Subramanian et. al. Adv. Mater. 18, 1737 (2006) 45

46 LnFe 2 O 4 Temperature dependence of magnetization in YFe 2 O 4 at 100 Oe Frequency dispersion of Dielectric constant in YFe 2 O 4 C R Serrao, J R Sahu, K Ramesha and C N R Rao J. Appl. Phys. 104, (2008) 46

47 LnFe 2 O 4 Frequency dispersion of Dielectric constant in Y 0.5 Lu 0.5 Fe 2 O 4 Frequency dispersion of Dielectric constant in YbFe 2 O 4 C R Serrao, J R Sahu, K Ramesha and C N R Rao J. Appl. Phys. 104, (2008) 47

48 LnFe 2 O 4 Frequency dispersion of Dielectric constant in ErFe 2 O 4 Magnetocapacitance effect in YFe 2 O 4 C R Serrao, J R Sahu, K Ramesha and C N R Rao J. Appl. Phys. 104, (2008) 48

49 LnFe 2 O 4 Magnetocapacitance effect in YFe 2 O 4 Magnetocapacitance effect in Y 0.5 Lu 0.5 Fe 2 O 4 C R Serrao, J R Sahu, K Ramesha and C N R Rao J. Appl. Phys. 104, (2008) 49

50 Rare Earth Manganates Ln 1-x A x MnO 3 La 0.7 Ca 0.3 MnO C M CHARGE ORBITAL ORDERING SIZE DISORDER (Paul PHASE SEPARATION 50

51 Nd 0.5 Ca 0.5 MnO MnO 3 Nd 0.5 Sr 0.5 MnO MnO 3 Rao et. al., Phys. Rev. B (2000) Woodward and Rao Chem. Mater. (2001) 51

52 CHARGE-ORDERED STATE 1. Magnetic field 2. Pressure (external/internal) 3. Radiation 4. Electric field 5. Chemical substitution FERROMAGNETIC METALLIC STATE 52

53 Electronic Phase Separation Hatched Area FMM (a) (b) (c) (d) Shenoy and Rao, ChemPhysChem (2006) [Perspective], Phil. Trans. Royal Soc. London (2008) 53

Magnetic ferroelectricity due to Charge-ordering (Manganates) (a) (b) (c) (a) Site-centred charge order, (b) bond-centred charge order (the Zener polaron state), and (c) a ferroelectric intermediate

54 Magnetic ferroelectricity due to Charge-ordering (Manganates) (a) (b) (c) (a) Site-centred charge order, (b) bond-centred charge order (the Zener polaron state), and (c) a ferroelectric intermediate state. The charge-ordered structure in (c) lacks inversion symmetry. Thin green arrows indicate the dipole moments of horizontal and vertical dimers, and the diagonal arrow is the total ferroelectric moment. Efremov et. al., Nat. Mater., 3, 853 (2004). 54

55 Nd 0.5Ca MnO 3 Nd 0.5 Ca 0.5 MnO 3 has a CO transition at 240 K and AFM transition at 140 K Magnetocapacitance effect in Nd 0.5 Ca 0.5 MnO 3 C R Serrao, A Sundaresan and C N R Rao, J. Phys: Cond. Matter. 19, (2007). 55

56 Pr 0.6Ca MnO 3 Pr 0.6 Ca 0.4 MnO 3 has a CO transition at 240 K and AFM transition at 170 K Magnetocapacitance effect in Pr 0.6 Ca 0.4 MnO 3 C R Serrao, A Sundaresan and C N R Rao, J. Phys: Cond. Matter. 19, (2007). 56

57 Y0.5Ca MnO 3 (SCO) Most insulating manganite Temperature variations of the dielectric constant of Y 0.5 Ca 0.5 MnO 3 Magnetocapacitance effect in Y 0.5 Ca 0.5 MnO 3 J R Sahu, C R Serrao, A Sundaresan and C N R Rao (unpublished results) 57

58 Y0.55Ca 0.45MnO MnO 3 Temperature variations of the dielectric constant of Y 0.55 Ca 0.45 MnO 3 Magnetocapacitance effect in Y 0.55 Ca 0.45 MnO 3 J R Sahu, C R Serrao, A Sundaresan and C N R Rao (unpublished results) 58

59 Y0.55Ca 0.45MnO MnO 3 Hysteresis loop J R Sahu, C R Serrao, A Sundaresan and C N R Rao (unpublished results) 59

60 Y0.55Ca 0.45MnO MnO 3 SHG Measurements Quartz 1.00 Y 0.55 Ca 0.45 MnO Note: These materials donot show Magnetoresistance Therefore these Manganites are Multiferroic and Magnetoelectric J R Sahu, C R Serrao, A Sundaresan and C N R Rao (unpublished results) 60

61 Rare Earth Manganites Another proof of Multiferroicity Electric field induced Magnetic Flux Guha, Khare, Raychaudhuri and Rao, Phys. Rev. B 62, R11941 (2000) 61

62 Oxide nanoparticles Surface ferromagnetism All oxide nanoparticles (even non magnetic ones, such as Al 2 O 3 ) show Surface ferromagnetism Sundaresan and Rao, Phys. Rev. B 74, (2006) 62

63 Surface ferromagnetism in BaTiO 3 Nanoparticles of BaTiO 3 also show surface ferromagnetism! Sundaresan, Waghmare and Rao (2008) 63

64 Multiferroic BaTiO 3 nanoparticles P E hysteresis curve of nanocrystalline BaTiO 3 Magnetocapacitance in nanocrystalline BaTiO 3 Sundaresan, Waghmare and Rao (2008) 64

65 Outlook 65

66 THANK YOU 66

Charge-order driven multiferroic and magneto-dielectric properties of rare earth manganates

Bull. Mater. Sci., Vol. 33, No. 2, April 2010, pp. 169 178. Indian Academy of Sciences. Charge-order driven multiferroic and magneto-dielectric properties of rare earth manganates CLAUDY RAYAN SERRAO 1,2,