Spin-valve System Research Articles

Magnetoresistance, Hall effect, and thermoelectric power in spin valves

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.

Magnetic alignment in spin-valve system studied by polarized neutron reflectometry

Exchange biased spin-valve systems with the nominal structure: 5 × [Ta (3.5 nm)/Ni 80Fe 20 (8 nm)/Cu ( t)/Ni 80Fe 20 (6 nm)/Fe 50Mn 50 (10 nm)/Ta (3.5 nm)], for t = 1.0 and 1.5 nm, were dc magnetron sputtered at 5 mTorr on Si(100). Similar systems with thicker Cu layers, are of interest for magnetoresistive read heads. The maximum in magnetoresistance is attributed to antiparallel alignment of the magnetization of the two Ni 80Fe 20 layers separated by the Cu layers. The magnetic alignment in this system as a function of field is investigated by Polarized Neutron Reflectometry (PNR), as this technique is sensitive to the magnetization as a function of depth. Rijks et al. [1] calculated the optimal orientation of the magnetization in both NiFe layers as a function of applied field. Models fitted to PNR data measured at various magnetic fields support these calculations.

Magnetic exchange-coupling effects in asymmetric trilayer structures of MBE-grown Co/Cr/Fe.

We present results of anisotropy and exchange-coupling studies of asymmetric Co/Cr/Fe trilayers and superlattices grown by molecular beam epitaxy on Cr(001)/Mg(001) buffers and substrates. The magnetic properties have been investigated using both the longitudinal magneto-optical Kerr effect and ferromagnetic resonance. The hysteresis data obtained from the trilayer system were fit to a theoretical model which contains both bilinear and biquadratic coupling. The effective in-plane anisotropy was found to be of fourfold symmetry with the same easy-axis orientation for both the Fe and Co layers. An analysis of the easy-axis hysteresis loops indicates long-period oscillatory coupling and also suggests a short periodic coupling. We show that weakly antiferromagnetically coupled asymmetric films might serve as potential candidates for improved spin-valve systems. \textcopyright{} 1996 The American Physical Society.

Inverse giant magnetoresistance (invited)

Inverse giant magnetoresistance (GMR) is obtained in multilayers alternating two ferromagnetic layers F1 and F2 with different asymmetry of spin scattering, α1≳1 and α2<1. This is clearly demonstrated in the simple spin-valve system with perpendicular magnetization Fe1−xVx/Au/Co. With respect to Fe, the FeV alloys with x=0.18 and 0.29 exhibit an inversion of the spin scattering coefficients (αFe≳1, αFeV<1) due to the change of the densities of states at the Fermi level. The inverse MR of FeV/Au/Co is studied as a function of FeV layer thickness and temperature and compared to calculations based on the Camley–Barnas model. The data show that the inverse GMR is due to the bulk scattering within the FeV layer, which coexists with a substantial interface scattering favoring normal GMR.

ハード磁性／ソフト磁性二層膜のスプリング磁化過程

The magnetization process and magnetoresistance were studied for hard-magnetic/soft-magnetic bilayers. The films demonstrate a reversible magnetization process. During the demagnetization process, the magnetic moments of the soft magnetic layer rotate reversibly, and the rotation angle becomes larger as the atomic layer moves further from the soft/hard interface. The magnetization process and the angle distribution were calculated by using the condition that the angle distribution gives the local minimum of magnetic energy at each magnetic field. We observed magnetoresistance effects that reflect the reversibility of the magnetization process. The bilayer with the reversible magnetization process was also applied to a spin-valve system.