Phys. Status Solidi RRL 5, No. 12, A119 A123 (2011) / DOI /pssr

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1 Phys. Status Solidi RRL 5, No. 12, A119 A123 (2011) / DOI /pssr Full text on our homepage at FRONT COVER Establishing magnetic oxides as spin-selective tunnel barriers on mainstream semiconductors opens up a promising route towards highly efficient spin injection and detection. Europium oxide (EuO) is the only magnetic oxide predicted to be stable in direct contact with silicon. A throughout hard X-ray photoemission spectroscopy study (see the Letter by Caspers et al. on pp ) reveals the nearly ideal stoichiometry of EuO spin filter tunnel barriers grown by Oxide-MBE, with no silicon oxide or silicide formation being observed at the EuO/Si interface. This result clearly demonstrates the successful integration of a magnetic oxide tunnel barrier with silicon, opening up the future integration of magnetic oxides into functional spintronics devices. BACK COVER Eggeling et al. (pp ) investigated the size and magnetic free layer dependence of the vortex dynamics in relatively large spin-valve nanocontacts. A circular nanocontact confines the current flow through a spin-valve multilayer (upper cover image) incorporating a magnetic free layer and an unpinned artificial antiferromagnet as polarizer. Spin-torque driven magnetic vortex dynamics are observed in dependence on the magnetic properties, the contact size and the applied current, provoking microwave oscillations at zero external magnetic field. The oscillation spectra (lower image) show the evolution of single and multiple radio frequency modes as a function of the nanocontact size. These specific properties make spin-torque-driven devices suitable e.g. for nano-sized microwave sources, ultra-compact magnetic field sensors or fast and non-volatile magnetic memories. PREFACE Page A117 A118 S. N. Piramanayagam, Jagadeesh Moodera, Russell Cowburn, and Rachid Sbiaa Focus on Spintronics and Spin Physics NEW IN pss Page A124 Page A125 Page A127 A128 Recent and forthcoming publications in pss Conference calendar Information for authors

2 physica status solidi rrl A120 Page R. Sbiaa, H. Meng, and S. N. Piramanayagam Materials with perpendicular magnetic anisotropy for magnetic random access memory In this Review, the princple of spin-transfer torque magnetic random access memory (STT-MRAM) is explained: The magnetic tunnel junction device is sandwiched between two electrodes (cross-point architecture). The writing is based on the spin torque effect and the reading on tunnelling magnetoresistive effect. In contrast to field-based MRAM, the STT-MRAM does not require an external magnetic field. Since STT-MRAM is scalable, the transistor scales down with the device size. Materials with perpendicular magnetic anisotropy (PMA) are being investigated for their use in STT-MRAM multilayers such as Co/Pd and Co/Pt as well as FeCoB and future candidates such as FePt. RAPID RESEARCH LETTERS Page Alexander Makarov, Viktor Sverdlov, Dmitry Osintsev, and Siegfried Selberherr Reduction of switching time in pentalayer magnetic tunnel junctions with a composite free layer In this Letter the authors report a substantial decrease of the switching time in a pentalayer structure with a composite-free layer as compared to the pentalayer structure of similar dimensions with a monolithic free layer. The physical reasons for the switching time reduction at the same current density are discussed. Page Sylvain D. Brechet and Jean-Philippe Ansermet Heat-driven spin currents on large scales Brechet and Ansermet show that a three-current model of heat, spin-up and spin-down currents predicts the spin polarisation current to exist on large scales and to be proportional to the temperature gradient, corresponding to a spin Soret effect. They establish the existence of the spin current driven by a heat current over large distances in the absence of a charge current and at equilibrium of the spin channels. Thus, a heat current may also affect the magnetisation.

3 Phys. Status Solidi RRL 5, No. 12 (2011) A121 Page Taiebeh Tahmasebi, Seidikkurippu N. Piramanayagam, Rachid Sbiaa, Hang Khume Tan, Randall Law, Sunny Lua, and Tow Chong Chong Tailoring the growth of L1 0 -FePt for spintronics applications Ordered L1 0 -FePt with large magnetocrystalline anisotropy (K u ) and high saturation magnetization (M s ) enables potential scaling of spintronic devices down to 5 nm. FePt films need to be smooth and possess good (001) texture in order to achieve the desired properties for spintronics applications. This Letter focuses on the tailoring of L1 0 -FePt growth for such applications. The L1 0 -FePt magnetic layers deposited on Pd seed layers exhibit large ordering parameter, smoothness and strong perpendicular magnetic anisotropy. Page Sophie A. Morley, Nicholas A. Porter, and Christopher H. Marrows Magnetism and magnetotransport in sputtered Co-doped FeSi films Microelectronics manufacturing relies on planar processing for which thin films are needed. Sputtered films of cobaltdoped iron monosilicide have been fabricated and characterised. The non-centrosymmetric ε-phase is the predominant form of the material after annealing. It shows similar magnetic and magnetotransport properties to bulk single crystals in spite of the inherent disorder in a thin film. This includes a ratio of magnetic moment to carrier density of approximately unity, suggesting a high spin-polarisation in this silicon-based material. Page S. M. Mohseni, S. R. Sani, J. Persson, T. N. Anh Nguyen, S. Chung, Ye. Pogoryelov, and Johan Åkerman High frequency operation of a spin-torque oscillator at low field In this Letter the authors demonstrate a nanocontact spin-torque oscillator (STO) based on an orthogonal spinvalve architecture with an in-plane Co polarizer and an out-of-plane Co/Ni multilayer free layer. High frequency operation at low external fields is achieved by tailoring the Co/Ni layer properties to increase the strength of the perpendicular magnetic anisotropy, while simultaneously reducing the saturation magnetization.

4 physica status solidi rrl A122 Page Moritz Eggeling, Theodoros Dimopoulos, Rudolf Heer, and Hubert Brückl Magnetic vortex excitation dependence on the magnetic free layer and size of spin-valve nanocontacts Spin-torque-driven vortex-oscillators can be applied as nano-sized microwave sources, ultra-compact magnetic field sensors or in fast and non-volatile magnetic memories. This Letter demonstrates the dependence of vortex dynamics on the free layer and the size of relatively large spin-valve nanocontacts, incorporating an unpinned artificial antiferromagnet. Nucleation current density, multiple mode excitation and magnetic field dependence are specifically addressed. Page Michael Lorenz, Matthias Brandt, Katja Mexner, Kerstin Brachwitz, Michael Ziese, Pablo Esquinazi, Holger Hochmuth, and Marius Grundmann Ferrimagnetic ZnFe 2 O 4 thin films on SrTiO 3 single crystals with highly tunable electrical conductivity Within the current search for spintronic materials with spin polarized conductivity, zinc ferrite (ZnFe 2 O 4 ) thin films grown on SrTiO 3 (001) and (111) single crystals are highly promising as magnetic semiconducting electrode in advanced all-oxide tunnel junctions and field effect transistors, as well as insulating barrier in spin filters. This is due to the highly tunable electrical conductivity coupled with high saturation magnetization. Page C. Caspers, M. Müller, A. X. Gray, A. M. Kaiser, A. Gloskovskii, C. S. Fadley, W. Drube, and C. M. Schneider Electronic structure of EuO spin filter tunnel contacts directly on silicon Hard X-ray photoemission spectroscopy reveals the nearly ideal stoichiometry of EuO spin filter tunnel barriers grown directly on silicon, and the absence of silicon oxide formation at the EuO/Si interface. These results demonstrate the successful integration of a magnetic oxide tunnel barrier with silicon, paving the way for the future integration of magnetic oxides into functional spintronics devices.

5 Phys. Status Solidi RRL 5, No. 12 (2011) A123 Page M. Ziese A spin-calorics device based on La 0.7 Sr 0.3 MnO 3 /SrRuO 3 superlattices In this Letter a spin-caloric device is proposed that consists of a wedge-shaped La 0.7 Sr 0.3 MnO 3 /SrRuO 3 superlattice (SL). Studies of SLs with various layer thicknesses show that the magnetic work can be strongly influenced by the engineering of the crystalline symmetry or the use of exchange biasing. A SL wedge in a rapidly varying magnetic field should therefore support a self-sustained Seebeck effect. Page H. S. Hsu, Y. Tung, Y. J. Chen, M. G. Chen, J. S. Lee, and S. J. Sun Defect engineering of room-temperature ferromagnetism of carbon-doped ZnO Room-temperature ferromagnetism observed in an air-annealed C:ZnO sample was associated with a ferromagnetic magnetic circular dichroism peak. This is related to the loss of carbon and the creation of defects in an air-annealed C:ZnO film by the reaction between carbon dopants and oxygen. In this Letter the authors suggest that a combination of carbon doping and a suitable post-annealing treatment has a strong impact on the defect-mediated ferromagnetism of C:ZnO. Page N. Sedlmayr, V. K. Dugaev, M. Inglot, and J. Berakdar Indirect interaction of magnetic domain walls E(R,q) mev q=p/4 q=p In this Letter the authors calculate the carrier-mediated interaction between domain walls in a ferromagnetic strip. The result is an oscillating function of both the interdomain wall distance and their relative orientations. Sedlmayr et al. go on to show how this can give rise to spiralling domain wall orientations in a strip. Such an interaction can have consequences for any tightly packed wire of domain walls R/l physica status solidi (RRL) is indexed in Cambridge Scientific Abstracts (CSA); Chemical Abstracts Service/ SciFinder (ACS); Current /Physical, Chemical & Earth Sciences, Materials Science Citation Index, Science Citation Index, Science Citation Index Expanded, Web of Science (Thomson ISI); FIZ Karlsruhe Databases (FIZ Karlsruhe); INSPEC (IET); SCOPUS (Elsevier); VINITI (All-Russian Institute of Science & Technological Information).