Quantitative Temperature Dependence of Longitudinal Spin Seebeck Effect at High Temperatures

This article reports temperature-dependent measurements of longitudinal spin Seebeck effects (LSSEs) in Pt/Y$_3$Fe$_5$O$_{12}$ (YIG)/Pt systems in a high temperature range from room temperature to above the Curie temperature of YIG. The experimental results show that the magnitude of the LSSE voltage in the Pt/YIG/Pt systems rapidly decreases with increasing the temperature and disappears above the Curie temperature. The critical exponent of the LSSE voltage in the Pt/YIG/Pt systems at the Curie temperature was estimated to be 3, which is much greater than that for the magnetization curve of YIG. This difference highlights the fact that the mechanism of the LSSE cannot be explained in terms of simple static magnetic properties in YIG.Comment: 9 pages, 5 figures, 1 tabl

Atomic-level structural change in Ni-Ti alloys under martensite and amorphous transformations

The Ni-Ti alloys have been used widely as functional materials, especially for the purpose of superelastic behavior or shape memory effect. It has been believed that martensitic transformation (MT) between crystals plays a major role in the phase transition behavior, but recent experimental observation shows that there also exists stable amorphous structure. Detailed information of the atomic-level change, that is microscopic crystalline rearrangement of Ni-Ti alloys in applied shear deformation is needed. Our study aims at clarifying those atomic mechanisms by using molecular dynamics (MD) simulations. For Ni-Ti alloys, we assess the possibility of the modified version of EAM (MEAM) with parameters for Ni-Ti. We construct MD models to investigate both MT and amorphization in Ni-Ti alloys. We devise a method based on so-called common neighbor analysis (CNA) to effectively detects amorphous atoms, by finding clusters with five-folded symmetry (pentagonal bipyramids). In comparing models with different crystal orientation, when crystalline slip is not easy due to small resolved shear stress, the atoms in initial B2 or B19’ structure tend to be rearranged with rotational motion and transform to amorphous atoms. Besides, there are ”pre-amorphous” structures as a symptom of major and later increase of amorphous atoms

Theory of magnon-driven spin Seebeck effect

The spin Seebeck effect is a spin-motive force generated by a temperature gradient in a ferromagnet that can be detected via normal metal contacts through the inverse spin Hall effect [K. Uchida {\it et al.}, Nature {\bf 455}, 778-781 (2008)]. We explain this effect by spin pumping at the contact that is proportional to the spin-mixing conductance of the interface, the inverse of a temperature-dependent magnetic coherence volume, and the difference between the magnon temperature in the ferromagnet and the electron temperature in the normal metal [D. J. Sanders and D. Walton, Phys. Rev. B {\bf 15}, 1489 (1977)].Comment: 10 pages, 3 figures, 2 tables. This version is NOT the published PRB but a version with an erratu