MgO based specular spin valve with reversible minor loop and higher exchange bias for futuristic linear magnetic field sensor

Abstract

Specular spin valves (SVs) containing ultrathin MgO, structured as substrate/seed/AF/PL1/MgO/PL2/Cu/FL/MgO/cap, have been fabricated. Both structural and magnetic characterizations of MgO based specular spin valve (SSV) have been performed and compared them with the measured data on naturally oxidized (NO) and conventional spin valves (CSV), grown under optimised condition. Reversible minor loop characteristics, highest exchange bias of 625 G and 10% magnetoresistive (MR) ratio were important observations in MgO based system. Zero hysteresis behavior was confirmed due to the reduction of grain growth of the stacks above the fine-textured MgO layer, through X-ray diffraction measurements. Interestingly, at 10 K, above 100% enhancement in MR ratio was observed in MgO based system with marginal increase in coercivity of the order 1 G. On the other hand, NO based structure has 10% MR, minor loop hysteresis of ∼2 G and exchange bias of ∼560 G at room temperature; however at 10 K, only 75% enhancement in MR ratio with large anomalies in magnetic measurements attributes due to the AFM nature of oxide materials. The above studies reflects the superior performance of MgO based SSV over a wide range of temperature in comparison to other SV structures and may lead to futuristic linear magnetic field sensor applications.