X. F. Jin

Longitudinal spin Seebeck effect free from the proximity Nernst effect.

This Letter provides evidence for intrinsic longitudinal spin Seebeck effects (LSSEs) that are free from the anomalous Nernst effect (ANE) caused by an extrinsic proximity effect. We report the observation of LSSEs in Au/Y(3)Fe(5)O(12) (YIG) and Pt/Cu/YIG systems, showing that the LSSE appears even when the mechanism of the proximity ANE is clearly removed. In the conventional Pt/YIG structure, furthermore, we separate the LSSE from the ANE by comparing the voltages in different magnetization and temperature-gradient configurations; the ANE contamination was found to be negligibly small even in the Pt/YIG structure.

Evolution of magnetic anisotropy in epitaxial Fe films by ferromagnetic resonance

Single-crystal Fe films of 4 to 33 monolayers (ML) on GaAs (100) prepared by molecular-beam epitaxy were studied by ferromagnetic resonance (FMR). The evolution of both in-plane and out-of-plane anisotropies was observed. The FMR data show a predominant in-plane uniaxial magnetic anisotropy in the films with the thickness t less than 12.7 ML, with an easy axis along the 〈11_0〉 direction. An in-plane fourfold anisotropy due to cubic magnetocrystalline anisotropy starts to appear and coexists with uniaxial magnetic anisotropy when t=8.4 ML, and increases with increasing film thickness. For t=33 ML, the cubic anisotropy constant K1 reaches 28.2×104 erg/cm3, which is 60% of the value for bulk bcc Fe. A strong perpendicular anisotropy in the ultrathin Fe films was observed. For t=4 ML, the perpendicular anisotropy constant is as high as 14.6×106 erg/cm3. It decreases with increasing the thickness t and reaches about 2.1×106 erg/cm3 for 33 ML, while a small fourth-order perpendicular anisotropy appears and incr...

Abnormal magnetic transport in Co/Mn/Co sandwiches

A series of Co/Mn/Co sandwiches was prepared on GaAs(001) surfaces at room temperature via a molecular beam epitaxy (MBE) technique. Reflection high-energy electron diffraction (RHEED) and x-ray-diffraction (XRD) analysis indicated a polycrystalline structure. By standard magnetoresistance measurements, it was found that with a Mn spacer thickness of 8 A, a seldom-seen positive magnetoresistance (PMR) as high as 16% was exhibited at room temperature. The measurement under different geometries of H and I indicated that it was not an anisotropic magnetoresistance (AMR) effect. The MR–H curve displayed no hysteresis in contrast to the magnetometry measurement. An interface effect is proposed as a possible origin of this phenomenon.

Concurrent variation of giant magnetoresistance and saturation Kerr rotation in NiCo/Cu multilayers

The dependences of magneto-optical effect, effective optical constants, and giant magnetoresistance (GMR) on the thickness of Cu layers were investigated in NiCo/Cu multilayers prepared by rf magnetron sputtering. A peak of saturation polar Kerr rotation θK, occurred simultaneously with that of GMR ratio when the Cu thickness is around 1.0 nm, where a clear drop of the effective optical constants n and k appeared. The peak of θK is mainly caused by the reduction of the effective optical constants, which dominate over the small drop of the effective off-diagonal elements of the dielectric tensor. The concurrent variation of GMR and θK is related to antiferromagnetic interlayer coupling, which may change the electron band structure and thus the optical and magneto-optical transitions of electrons.

Epitaxial structure and magnetic anisotropies of metastable single crystal Co0.70Mn0.30 film

Alloy films of Co0.70Mn0.30 were grown on GaAs (001) substrates by molecular beam epitaxy at room temperature. The metastable tetragonally distorted single crystal structure was confirmed by reflection high energy electron diffraction and x-ray diffraction measurement, which exhibited a 2.87 A in-plane lattice parameter. Ferromagnetic resonance measurements and theoretical fitting were performed and showed that, with a Mn capping layer, a uni-directional anisotropy existed. In addition, a fourfold tetragonal magnetocrystalline anisotropy as well as a uniaxial term in the film plane was also confirmed. The hysteresis loops recorded by longitudinal magneto-optical Kerr-effect also demonstrated the existence of different kinds of in-plane magnetic anisotropy. The origins of the anisotropy are explained tentatively.

Magnetooptical, optical and GMR effect in Ni–Co/Cu multilayers

Abstract A series of RF sputtered NiCo/Cu multilayers was prepared and the correlation of the interlayer coupling and magnetooptical Kerr effect (MOKE) was studied. A concurrent oscillation of the magnetoresistance ratio and the maximum Kerr rotation ( θ 2 k + η 2 k ) 1/2 with Cu layer thickness was observed. The oscillation of the Kerr rotation is attributed to changes in the band structure related to the antiferromagnetic interlayer coupling, leading to changes in the optical and magnetooptical transitions.

Correlation between spin reorientation transition and Curie temperature of NixPd1-x alloy on Cu(001)

The correlation between spin reorientation transition SRT and Curie temperature of NixPd1−x alloy on Cu 001 was investigated by ac susceptibility and magneto-optic Kerr-effect measurements. The result shows that NixPd1−x alloy exhibits a SRT at Ni concentration of 87% for 9 ML and of 96% for 7 ML. No reduction in Curie temperature was observed in the region of SRT as declared by F. Matthes et al. J. Appl. Phys 91, 8144 2002 . In addition it was found that Curie temperature increased with Ni concentration in different trends before and after SRT, which are attributed to the anisotropy variation.

OSCILLATIONS OF INTERLAYER COUPLING AND MAGNETO-OPTICAL KERR EFFECT IN NICO/CU MULTILAYERS

A series of rf sputtered [NiCo(1.3 nm)/Cu(tCu)]25 multilayers with tCu=0.5–4.0 nm was prepared and the behavior of interlayer coupling, magnetoresistance, and magneto-optical Kerr effect was studied. A concurrent oscillation in the magnitude of the magnetoresistance and magneto-optical Kerr effect in visible wavelength range as a function of Cu layer thickness was observed. The changes of both the optical and magneto-optical transition due to interlayer coupling may be responsible for the magneto-optical activities.