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Current-perpendicular-to-plane magnetoresistance (CPP-MR) devices using a Co2Fe(Ga0.5Ge0.5) Heusler alloy as ferromagnetic electrodes and a Ag/Mg-Ti-O (MTO)/Ag tri-layer as a spacer are studied. A large voltage output of 16 mV with a magnetoresistance ratio of 46% and resistance-area product RpA in the parallel magnetization state of approximately 200 mΩ μm2 are obtained. The microstructure characterization reveals that upon annealing at 550 °C, nanoscale Ag channels are formed penetrating the MTO layer, which are responsible for the large MR output. At room temperature, for all the devices, RpA decreases with increasing the bias voltage Vb, which is contradictory to the conventional CPP-giant magnetoresistance devices with a current-confined-path structure, in which the RpA increases with increasing Vb. Such a Vb dependence of RpA is in accordance with the temperature dependence of RpA. These results suggest that the magneto-transport channels comprise semiconducting current confined paths, bringing new perspectives for the design and engineering of CPP-MR devices with conductive oxides-based multilayer spacers. [ABSTRACT FROM AUTHOR]

The near-future ultra-high-density magnetic recording with an assist recording technology requires a substantial evolution of the read-head technology. A read sensor with a small sensor resistance-area product ( $RA$ ), a large magnetoresistance ratio ( \Delta R/R$ ), and a thin total sensor thickness is required for the low bit error rate and high-spatial resolution of reading. We developed current-perpendicular-to-plane giant magnetoresistance sensors using highly spin-polarized Heusler alloy ferromagnetic layers with the spin polarization of the conducting electron \beta \sim 0.8$ . A reasonably large \Delta R/R$ up to 14% was obtained by a practical bottom-pinned spin-valve structure with a conventional metallic spacer layer of an Ag90Sn10 (AgSn) alloy. By replacing the spacer layer with a conductive oxide-based AgSn/InZnO bilayer, a large \Delta R/R , which is optimal for the read sensor application. A large voltage output up to 6 mV was obtained for a sensor utilization of ~33% at a bias voltage of 100 mV. [ABSTRACT FROM PUBLISHER]

This article reviews progress in magnetoresistive (MR) read sensor technology for hard-disk drives (HDDs). MR reader technology has progressed from the anisotropic magnetoresistance sensor, to the current-in-plane giant magnetoresistive (CIP-GMR) sensor, to today’s current-perpendicular-to-plane (CPP) tunneling magnetoresistance (TMR) sensor. This evolution has driven the continuous growth of the areal density of HDDs from 2 Gbpsi (gigabits/in2) in early longitudinal recording to ∼1 Tbpsi (terabits/in2) currently in perpendicular magnetic recording. For further increases in the areal density, a transition to energy-assisted recording is expected in the near future. Further technical challenges for the read sensor technology toward 2 Tbpsi and then 5 Tbpsi areal densities are discussed based on recent promising experimental work on CPP-GMR using Heusler alloys, and CPP-GMR’s laterally expanded version, the lateral spin valve (LSV). To realize large MR output and narrow shield-to-shield spacing requirements for higher density recording, materials selection and optimization of interface structures of CPP-GMR and LSV devices are critical. [ABSTRACT FROM PUBLISHER]

Current-perpendicular-to-plane giant-magnetoresistance effect in a ferromagnetic/nonmagnetic multilayer is studied theoretically by solving the diffusion equation of the spin accumulation without assuming the periodic boundary condition. We show that the Valet and Fert theory underestimates spin asymmetries with decreasing the number of layers. [ABSTRACT FROM AUTHOR]