Nano-oxide-layer insertion and specular effects in spin valves: Experiment and theory

Abstract

We report a systematic study of NOL ͑nano-oxide-layer͒ insertion and specular effects on the giant magnetoresistance ͑GMR͒ of single, synthetic, and dual spin valves, using a semiclassical Boltzmann theory. It is confirmed that the GMR ratio is enhanced by NOL insertion inside the pinned layer or after the free layer. The enhancements are primarily due to the contribution of the majority carriers. The NOL insertions inside the inactive layers of spin valves such as the seed, under, and capping layers reduce the GMR ratio. Though introducing a NOL before or after the Cu spacer would, in principle, significantly suppress the GMR ratio due to the blocking effect or the average effect of different spin channels, large positive or negative ͑inverse͒ GMR is found by assuming spin-dependent NOL specular reflections. We have also demonstrated that specular reflection, even beyond a capping layer, may result in reduction of GMR. Upon appropriate NOL insertion, the amplitude of curve of GMR versus thickness of individual layer of spin valves may be generally enhanced, but the shape may change, depending on whether the distance of the NOL to the layer is small or large ͑distance effect͒. Finally, it is found that most results obtained for the single realistic spin valves are applicable to synthetic and dual spin valves.

Influence of nano-oxide layer on the giant magnetoresistance and exchange bias of NiMn/Co/Cu/Co spin valve sensors

“…Figure 7͑a͒ shows that the GMR increases as the NOL position approaches the Co/NiMn interface. This result compares well with the findings of Wang et al 19 on CoFe/Cu/CoFe spin valves and Suh and Ross 20 on NiFe/Cu/Co ͑pseudo͒ spin valves. Wang et al have also observed that the GMR vanishes when the NOL approaches the interface between the pinned FM layer and the Cu spacer layer.…”

“…The increase in the GMR can be attributed to the specular electron scattering at the Co/NOL interface. The relative increase in 20 % and the absolute GMR values compare well with the results of Wang et al 19 obtained for IrMn/CoFe/Cu/CoFe spin valves. Wang et al find a maximum increase in the GMR from 6% to about 9 % by inclusion of the NOL in the pinned CoFe layer.…”

An Early Cancer Diagnosis Platform based on Micro-magnetic Sensor Array Demonstrates Ultra-high Sensitivity

“…This allows both magnetizations either parallel (low resistance) or antiparallel (high resistance) to be obtained with an externally applied magnetic field. The nano-oxide layer NOL inserted either adjacent to the pinned layer or free layers [46][47][48] can highly enhance the majority spin orientated electrons specularly scatter at NOL [49,50] and thus a high dR/R.…”

Effect of nano-oxide layers on giant magnetoresistance in pseudo-spin-valves using Co2FeAl electrodes

“…The nano-oxide layers (NOLs) were widely employed in conventional pseudo-SVs (PSVs) to extend the mean free path of majority spin-polarized electrons through specular electron scattering at the NOL/pinned (free) layer interface and enhance GMR ratio [14][15][16][17][18][19][20]. To date, there is no report on NOL-based SVs or PSVs with full-Heusler alloy electrodes.…”