Anup G. Roy

Advanced Dual-Free-Layer CPP GMR Sensors for High-Density Magnetic Recording

All-metal current-perpendicular-to-plane (CPP) giant magnetoresistance (GMR) read sensors with a shield-to-shield spacing (S2S) of 16-21 nm and a narrow track width of down to 25 nm were fabricated using ferromagnetic CoFeMnSi Heusler-alloy-based spin valves. Room temperature GMR ratios from these read sensors are obtained of up to 6% and 14-24% (ARA = 7.1-12.0 mΩμm2) at S2S = 16 and 21 nm, respectively. Studies and results of electron transport and CPP GMR support the sustainability and scalability of the CPP GMR process for Tb/in2 the areal density of magnetic recording. A universal parameter defined as magnetic resistivity for a sensor device, ΔRA/S2S in ohm micrometers, is proposed to gauge the practically and rationally applicable CPP GMR for the read sensor process. The investigation of the CPP GMR operation range and micromagnetic simulation demonstrates the feasibility of the CPP GMR read sensors at S2S = 21 nm for sustaining 1.0 Tb/in2 and of those at S2S = 16 nm for marginally supporting 2.0 Tb/in2 the areal density of magnetic recording, The future path to and potential of the technology for ever increasing areal density beyond 2.0 Tb/in2 are addressed with emphasis on the importance of further enhancing the CPP GMR for process margin improvement.

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

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, Co2MnSi 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 μm2, 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/in2 and beyond, for the time 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.

Effect of Substrate and Surface Conditioning on Magnetic Properties and Texture of CoPt Hard Bias Films

Effect of growth surface on CoPt hard bias film performance has been systematically studied using different substrates and substrate surface conditioning. Films deposited on four different types of substrates show different levels of crystallographic quality and magnetic performance. Among them, the films deposited on Al2O3-coated substrates are the best, up to 400 Oe higher in coercivity and 0.05 higher in remnant squareness. Proper substrate surface conditioning by ion-beam depositions has been found to be effective in improving inplace c-axis orientation; hence, magnetic properties of CoPt hard bias films. In addition, the deposition of a thin amorphous Al2O3 film on substrates prior to the hard bias film deposition helps to promote nearly 100% inplane c-axis crystallographic orientation.