We present direct evidence that the giant magnetocaloric effect recently discovered in the ${\mathrm{Gd}}_5{(\mathrm{S}\mathrm{i}}_{1.8}{\mathrm{Ge}}_{2.2})$ alloy is associated with a field-induced first-order structural transition from a ${P112\mathrm{}}_1/a$ monoclinic (paramagnetic) to a Pnma orthorhombic (ferromagnetic) structure. A large volume contraction of $\Delta V/V\cong 0.4\%$ takes place spontaneously at the transition temperature, $T_C\cong 240\mathrm{K}.$ The reported structural transition can be induced reversibly by application of an external magnetic field, producing strong magnetoelastic effects.

We present tunneling experiments on Fe(001)/MgO(20 Å)/FeCo(001) single-crystal epitaxial junctions of high quality grown by sputtering and laser ablation. Tunnel magnetoresistance measurements give 60% at 30 K, to be compared with 13% obtained recently on (001)-oriented Fe/amorphous-${\mathrm{Al}}_{\mathrm{2}}{\mathrm{O}}_3/\mathrm{FeCo}$ tunnel junctions. This difference demonstrates that the spin polarization of tunneling electrons is not directly related to the density of states of the free metal surface—Fe(001) in this case—but depends on the actual electronic structure of the entire electrode/barrier system.

We report that the first-order antiferromagnetic to ferromagnetic transition in the Ge-rich magnetocaloric compound ${\mathrm{Gd}}_5{(\mathrm{S}\mathrm{i}}_{0.1}{\mathrm{Ge}}_{0.9}{)}_4$ is associated with a structural phase transformation from a high-temperature ${\mathrm{Gd}}_5{\mathrm{Ge}}_4$-type Pnma to a low-temperature ${\mathrm{Gd}}_5{\mathrm{Si}}_4$-type Pnma orthorhombic structure. This magnetostructural transition can be triggered reversibly by application of an external magnetic field, resulting in strong magnetoelastic effects above the transition. The revised magnetic and crystallographic phase diagram for the ${\mathrm{Gd}}_5({\mathrm{Si}}_x{\mathrm{Ge}}_{1-x}{)}_4$ series is proposed.

The onset of a Griffiths-like phase has been observed in ${\mathrm{Tb}}_5{\mathrm{Si}}_2{\mathrm{Ge}}_2$ ($T_C=110\mathrm{K}$) by means of magnetic susceptibility and small-angle neutron scattering experiments. We show the growth of a ferromagnetic cluster system characterized by an inverse susceptibility exponent lower than unity at $T_C<T<T_G\approx 200\mathrm{K}$. We suggest that the Griffiths-like state is originated by local disorder within the crystallographic structure, stabilized and enhanced by competing intralayer and interlayer magnetic interactions. Both factors thus promote segregation of nanometric regions with ferromagnetic interactions.

We report the experimental observation of the spin Seebeck effect in magnetite thin films. The signal observed at temperatures above the Verwey transition is a contribution from both the anomalous Nernst (ANE) and spin Seebeck (SSE) effects. The contribution from the ANE of the Fe₃O₄ layer to the SSE is found to be negligible due to the resistivity difference between Fe₃O₄ and Pt layers. Below the Verwey transition, the SSE is free from the ANE of the ferromagnetic layer and it is also found to dominate over the ANE due to magnetic proximity effect on the Pt layer.