We present an infrared magneto-optical study of the highly thermoelectric narrow-gap semiconductor Bi2Se3. Far-infrared and mid-infrared (IR) reflectance and transmission measurements have been performed in magnetic fields oriented both parallel and perpendicular to the trigonal c axis of this layered material, and supplemented with UV-visible ellipsometry to obtain the optical conductivity σ1(ω). With lowering of temperature we observe narrowing of the Drude conductivity due to reduced quasiparticle scattering, as well as the increase in the absorption edge due to direct electronic transitions. Magnetic fields H c dramatically renormalize and asymmetrically broaden the strongest far-IR optical phonon, indicating interaction of the phonon with the continuum freecarrier spectrum and significant magnetoelectric coupling. For the perpendicular field orientation, electronic absorption is enhanced, and the plasma edge is slightly shifted to higher energies. In both cases the direct transition energy is softened in magnetic field. arXiv:0912.2769v2 [cond-mat.str-el]

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In bilayers consisting of Pd and yttrium iron garnet (Y(3)Fe(5)O(12) or YIG), we observe vanishingly small room-temperature conventional anisotropic magnetoresistance but large new magnetoresistance that is similar to the spin Hall magnetoresistance previously reported in Pt-YIG bilayers. We report a temperature dependence study of the two magnetoresistance effects in Pt-YIG bilayers. As the temperature is decreased, the new magnetoresistance shows a peak, whereas the anisotropic magnetoresistance effect starts to appear and increases monotonically. We find that the magnetoresistance peak shifts to lower temperatures in thicker Pd samples, a feature characteristic of the spin current effect. The distinct temperature dependence reveals fundamentally different mechanisms responsible for the two effects in such hybrid structures.

The structural and magnetic properties of sputter deposited epitaxial Fe 7.5 A Pt tPt 001 multilayers tPt = 0-15 A are investigated using x-ray di raction, Kerr magnetometry, and x-ray magnetic circular dichroism XMCD. Xray di raction shows that there is a crystalline phase change from bct to fct at a Pt thickness of 4 A. The Fe XMCD is enhanced by 10 over its bulk value for Pt thickneses from 1-4 A bct region, and depressed relative to the bulk by 10-20 after transition to the fct phase. The Pt layers show a striking almost ferromagnetic" behavior. XMCD at the N2;3 edge shows that the Pt moment is nearly constant u p to tPt = 1 0 A, with a value of 0.5 B atom. Kerr magnetometry is used to determine the in plane magnetocrystalline anisotropy constant, K1, as a function of tPt. It is found that for the Fe thickness studied here, the easy axis switches from the bct 100 to the bct 110 direction with increasing tPt. This indicates that K1 has a zero crossing, which occurs at tPt 1:5 A. This strong variation in magnetic anisotropy is attributed mainly to the Fe Pt interface region. However, ferromagnetic Pt also contributes a signi cant v olume anisotropy which w e estimate at-82 10 6 erg cc.

As a thin layer of palladium (Pd) is directly deposited on an yttrium iron garnet or YIG (Y 3 Fe 5 O 12 ) magnetic insulator film, Pd develops both low-and high-field magnetotransport effects that are absent in standalone Pd or thick Pd on YIG. While the low-field magnetoresistance peak of Pd tracks the coercive field of the YIG film, the much larger high-field magnetoresistance and the Hall effect do not show any obvious relationship with the bulk YIG magnetization. The distinct high-field magneto-transport effects in Pd are shown to be caused by interfacial local moments in Pd. JB g x x J J x J J J J x B B B J