Tuning morphology and magnetism in epitaxial L10-FePt films

In this work, well-ordered epitaxial FePt thin ¿lms have been grown by RF sputtering on two different substrates (MgO (100) and SrTiO3 (100)) and the effect of different lattice parameters between the substrate and FePt ¿lm on morphology and magnetic behavior has been considered. Growth conditions have been optimized to obtain different morphologies and magnetic behaviors

Observation of huge thermal spin currents in magnetic multilayers

Thermal spin pumping constitutes a novel mechanism for generation of spin currents; however their weak intensity constitutes a major roadblock for its usefulness. We report a phenomenon that produces a huge spin current in the central region of a multilayer system, resulting in a giant spin Seebeck effect in a structure formed by repetition of ferromagnet/metal bilayers. The result is a consequence of the interconversion of magnon and electron spin currents at the multiple interfaces. This work opens the possibility to design thin film heterostructures that may boost the application of thermal spin currents in spintronics

Phase diagram as a function of temperature and magnetic field for magnetic semiconductors

Using an extension of the Nagaev model of phase separation (E.L. Nagaev, and A.I. Podel'shchikov, Sov. Phys. JETP, 71 (1990) 1108), we calculate the phase diagram for degenerate antiferromagnetic semiconductors in the T-H plane for different current carrier densities. Both, wide-band semiconductors and 'double-exchange' materials, are investigated.Comment: 5 pages, 6 figures, RevTex, Accepted for publication in PR

Characteristic length scale of the magnon accumulation in Fe3O4/Pt bilayer structures by incoherent thermal excitation

The dependence of Spin Seebeck effect (SSE) with the thickness of the magnetic materials is studied by means of incoherent thermal excitation. The SSE voltage signal in Fe3O4/Pt bilayer structure increases with the magnetic material thickness up to 100¿nm, approximately, showing signs of saturation for larger thickness. This dependence is well described in terms of a spin current pumped in the platinum film by the magnon accumulation in the magnetic material. The spin current is generated by a gradient of temperature in the system and detected by the Pt top contact by means of inverse spin Hall effect. Calculations in the frame of the linear response theory adjust with a high degree of accuracy the experimental data, giving a thermal length scale of the magnon accumulation (¿) of 17¿±¿3¿nm at 300¿K and ¿¿=¿40¿±¿10¿nm at 70¿K

Direct epitaxial growth of polar Hf0.5 Zr0.5 O2 films on corundum

Single-phase epitaxial Hf0.5 Zr0.5 O2 films with non-centrosymmetric orthorhombic structure have been grown directly on electrode-free corundum (a-Al2 O3) substrates by pulsed laser deposition. A combination of high-resolution X-ray diffraction and X-ray absorption spectroscopy confirms the epitaxial growth of high-quality films belonging to the Pca21 space group, with 111] out-of-plane orientation. The surface of a 7-nm-thick sample exhibits an atomic step-terrace structure with a corrugation of the order of one atomic layer, as proved by atomic force microscopy. Scanning transmission electron microscopy reveals that it consists of grains with around 10 nm lateral size. The polar nature of this film has been corroborated by pyroelectric measurements. These results shed light on the mechanisms of the epitaxial stabilization of the ferroelectric phase of hafnia. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

On the nature of the (de)coupling of the magnetostructural transition in Er5_5Si4_4

In this report, a successful thermodynamical model was employed to understand the structural transition in Er$_5$Si$_4$, able to explain the decoupling of the magnetic and structural transition. This was achieved by the DFT calculations which were used to determine the energy differences at 0 K, using a LSDA+U approximation. It was found that the M structure as the stable phase at low temperatures as verified experimentally with a $\Delta F_0 = -$0.262 eV. Finally, it was achieved a variation of Seebeck coefficient ($\sim$ 6 $\mu$V) at the structural transition which allow to conclude that the electronic entropy variation is negligible in the transition.Comment: 17 pages, 3 figures, 1 tabl

Control of Structural and Magnetic Properties of Polycrystalline Co2FeGe Films via Deposition and Annealing Temperatures

: Thin polycrystalline Co2FeGe films with composition close to stoichiometry have been fabricated using magnetron co-sputtering technique. Effects of substrate temperature (TS) and postdeposition annealing (Ta) on structure, static and dynamic magnetic properties were systematically studied. It is shown that elevated TS (Ta) promote formation of ordered L21 crystal structure. Variation of TS (Ta) allow modification of magnetic properties in a broad range. Saturation magnetization ~920 emu/cm3 and low magnetization damping parameter α ~ 0.004 were achieved for TS = 573 K. This in combination with soft ferromagnetic properties (coercivity below 6 Oe) makes the films attractive candidates for spin-transfer torque and magnonic devices

Pressure dependence of the Griffiths-like phase in 5:4 intermetallics

We report a study of the effect of hydrostatic pressure (P) on the Griffiths-like phase in selected compounds of the R5(SixGe1 ? x)4 family of alloys (Tb4.925La0.075Si2Ge2 and Gd5Ge4) which present either the Gd5Si2Ge2-type (monoclinic, M) or the Sm5Ge4-type [orthorhombic-II, O(II)] structural phases at room temperature. The downward deviation in the inverse low-field dc susceptibility ??1 dc from the Curie-Weiss law below a characteristic temperature TG indicates that the Griffiths-like phase exists at pressures up to 10 kbar. From the obtained T-P phase diagrams, the pressure coefficient of the Griffiths-like temperature, dT G/dP, has been determined. These results are compared with those obtained in Dy5Si3Ge in a previous work. The dT G/dP coefficient is strongly dependent on the nature (first or second order) of the long-range order (FM or AFM) transition. This effect can be ascribed to a different structural character of the clusters within the Griffiths phase. A ratio of ?0.5 between the dT G/dP and the pressure coefficient of long-range magnetic ordering temperatures, dTC,N/dP (TC, ferromagnetic; TN , antiferromagnetic), is found in all the studied compounds.Work at the University of Zaragoza is supported by the Spanish Ministerio de Ciencia, Innovación y Universidades through Project No. MAT2017-82970-C2-2-R and the Aragon Regional Government (Grant No. E28_20R). Work at the University of Cantabria is supported by the Spanish Ministerio de Ciencia, Innovación y Universidades through Project No. MAT2017-83631-C3-R