Magnetic Heusler alloys and CPP GMR: Technology breakthrough and potential application in magnetic recording

摘要

Magnetic Heusler alloys that benefit from their half-metal characteristics have recently seen significant progresses in material researches and process development. As a result, current perpendicular to plane (CPP) giant magnetoresistance (GMR) has been proportionally enhanced, at least but not limited, by an order of magnitude in devices that contain such magnetic Heusler alloys and all-metal layer stacking. Amongst a wide selection of ferromagnetic Heusler alloys, CoMnSi and its variations show good process compatibility and high spin polarization that yields large CPP GMRs in spin valves. Recent experiments in Heusler alloy based spin valve structures epitaxially-grown on MgO (001) substrates have shown the room temperature ΔR/R can be as large as 75% in the CoMnFeSi Heusler alloy based pseudo spin valves grown on MgO (001) substrates. As a major application, CPP GMR reader technology has been extensively investigated in the last few years in response for the demand for increasing areal density in magnetic recording. One of recent industrial efforts shows that ΔR/R of 18 %, ΔRA= 9.0 mΩ μm, is achievable in the reader sensors fabricated using the same CoMnFeSi Heusler alloy based and antiferromagnetically pinned spin valves grown on AlTiC wafers. First and most important, this implication of these results is that the advance of technology provides large potential to the CPP GMR in future reader sensor development to accommodate all the requirements for SNR improvement and solution to spin torque effect induced instability in devices. Second, a large compromise in the CPP GMR is observed when the film stack or the reader sensor gap is reduced in thickness. This originates from the nature of stack-structure-dependent electron transport and process imperfectness and constraints in reader sensor building. With strict requirement for high areal density recording at 1TB/in and beyond, for the t- me being, dealing with this compromise with the scaling down of the reader sensor gap will be a major challenge and the focus of effort to better shape this technology as a success. This talk will briefly review and discuss recent magnetic Heusler material and reader sensor development and limiting factors that might affect the use of such magnetic material in device fabrication and operation.