Magnetoresistance, Hall effect, and thermoelectric power in spin valves

Abstract

Comparison of the magnetoresistance (MR) on two groups of spin-valve multilayers, NiO/NiFe/Cu/NiFe/Cu/NiO and NiO/NiFe/Cu/NiFe/Cu, has been made in order to investigate the possibility of the enhanced specular scattering at NiO/metal interface. No clear difference in MR between the two systems has been found, suggesting that the enhancement of specular scattering at interfaces is not the origin of the large MR. For the field direction almost perpendicular to the plane, we found a sensitive angular dependence of MR along with a large unidirectional anisotropy. To sort out any specific characteristics of the spin-valve system compared to the multilayers, thermoelectric power and Hall effect have been investigated for the first time.

Temperature dependence of the electrical and thermal transport in FeCo/Cu/Ni80Fe20 spin valves

“…Due to the affection of hybridization between sp and d electrons, increasing the electron energy results in increasing the electron velocity, thus yields both negative signs of S and ΔS. Owing to the similar mechanism, both negative signs of S and ΔS are also observed in other Co/Cu multilayers [7][8][9][10][11], Co-Ni/Cu multilayers [12], Ni 81 Fe 19 /Cu/Co spinvalve [17][18][19], CoFe/Cu/CoFe spin valve [31] and FeNi/ Cu/FeNi spin valve [16]. However, contrary to the Co/Cu system, the conductivity of Fe/Cr system is dominated by the minority spins, where the DOS at the Fermi level exhibits a pronounced valley.…”

“…Spin caloritronics is a new emerging research field to exploit the interactions among spin, charge, and heat currents in magnetic structures and devices [1]. Owing to combining the spin degrees of freedom associated to the electric charge and heat current, the transports under charge and heat have received renewed interest and been widely investigated in single ferromagnetic layer [2][3][4][5], ferromagnetic metal (F)/nonmagnetic metal (N) multilayers [6][7][8][9][10][11][12][13], spin valves [14][15][16][17][18][19] and magnetic tunnel junctions (MTJs) [20][21][22][23][24][25]. Similar to the charge current-driven magnetoresistance (MR) effect [26], the heat-driven thermoelectrical power (TEP) also depends on the magnetic states, indicating a spin-dependent Seebeck coefficient.…”

Spin Caloritronics in 3D Interconnected Nanowire Networks

“…As expected, the measured RT thermopower on the CPP-GMR Ni 80 Fe 20 /Cu sample in the saturated state (∼−25 µV/K) is only slightly smaller than the value found in the homogeneous Ni 80 Fe 20 NW network (∼−35 µV/K), in good agreement with Equation (1) and Figure 5b. In contrast, the RT Seebeck coefficients reported for Ni 80 Fe 20 /Cu multilayers in the CIP geometry (∼−10 µV/K) are much smaller [61]. A contrasting behavior has been observed in interconnected Ni/Cu NW networks.…”

Giant magnetothermopower of magnon-assisted transport in ferromagnetic tunnel junctions

“…1 The mismatch of spin currents at the interface between two ferromagnetic (F) electrodes with antiparallel spin polarizations produces a larger contact resistance than a junction with parallel polarizations, leading to tunneling magnetoresistance in F-F junctions 2,3 and giant magnetoresistance (GMR) in multilayer structures. 4,5 Systems displaying GMR have shown other magnetotransport effects including substantial magnetothermopower [6][7][8][9][10][11][12][13][14][15] with a strong temperature dependence. Thermoelectric effects have also been discussed in the context of spin injection across a ferromagnetic-paramagnetic junction.…”