Spin Valve Thin Films Research Articles

Noise in NiFeCo/Cu spin valve sensors

Noise properties of FeMn/NiFeCo/Cu/NiFeCo spin valve sensors have been investigated for various sensor widths. The spin valve thin films were patterned into stripes of varying widths from 2 μm to 20 μm. The width-to-length ratio was kept constant giving a fixed resistance of about 840 Ω. The spin valve sensors have been configured to allow signal and noise measurements to be performed using a bridge system. Noise measurement in spin valves with parallel anisotropy axes and cross anisotropy axes show field dependent noise near the high sensitivity region around zero bias field. In spin valves with parallel anisotropy axes, the noise increases with decreasing sensor width but for the cross anisotropy configuration, the noise decreases with decreasing sensor width. As the applied alternating field is increased, the noise peaks splits into two centred at zero bias. This can be explained in terms of a degenerate energy state.

Specularity in GMR spin valves and in situ electrical and magnetotransport measurements

An experimental four-point probe for in situ electrical and magnetotransport measurements during film growth is described. This method is unique in that it can capture thickness-dependent evolution of not only conductance but also magnetoresistance in a UHV deposition chamber. It has been used to monitor the growth of single layer, spin valve and multilayer structures and to measure specularity and interface scattering, both spin-independent and spin-dependent. Addition of /spl sim/1 monolayer of Co to Cu surface causes the net film conductance to decrease sharply, but the reverse case of Cu on Co shows a strong positive curvature of the thickness-dependent conductance. Most of the observed interface scattering may be intrinsic, arising from a high density of empty d-states at Cu boundaries that result in increased electron scattering. It is confirmed that exposing a spin valve or metal thin film to oxygen for an appropriate time may lead to an appreciable enhancement of specularity of its top surface. This leads to an increase in the sheet conductance, much more so when the free layer and pinned layer magnetizations are parallel than antiparallel. In contrast, previously reported specularity enhancement due to noble metal overlayers has not been observed by the in situ experiments.

Compositional variation of magnetoresistance characteristics in NiFe/Cu/Co spin valve thin films

Compositional variation of magnetoresistance characteristics in NiFe/Cu/Co spin valve thin films