Half-metal CPP GMR sensor for magnetic recording Z. Diao a,n , M. Chapline a , Y. Zheng a , C. Kaiser a , A. Ghosh Roy a , C.J. Chien a , C. Shang a , Y. Ding a , C. Yang a , D. Mauri a , Q. Leng a , M. Pakala a , M. Oogane b , Y. Ando b a Western Digital, 44100 Osgood Road, Fremont, CA 94539, USA b Department of Applied Physics, Tohoku University, Aoba-yama 6-6-05, Sendai, 980-8579, Japan article info Article history: Received 20 December 2012 Received in revised form 11 December 2013 Available online 30 December 2013 Keywords: Ferromagnetic Heusler alloy Half metallicity Magnetic spin valve Spin dependent electron transport CPP giant magnetoresistance Magnetic recording abstract Current-perpendicular-to-plane (CPP) giant magnetoresistance in magnetic CoFeMnSi Heusler alloy based spin valves and its potential application for high areal density recording are investigated, given that film stack design and crystalline structure matching during film growth are considered. Modeling of electron transport in spin valves predicts the CPP GMR of up to 130% and 25% in pseudo and antiferromagnet pinned spin valves at large bulk diffusive scattering asymmetry in Heusler alloy layers. Experimentally, the testing structures of pseudo spin valves, which have the L2 1 ordered Huesler alloy layers grown on single crystal MgO substrates, were built and demonstrate the CPP GMR of 55% or larger with ΔRA Z27.5 mΩμm 2 . CPP GMR reader sensors were fabricated based on antiferromagnet pinned spin valves using the same Huesler alloy materials albeit on AlTiC wafers, with narrow track widths of down to 35 nm. The CPP GMR obtained is up to 13% (18%, ΔRA ¼9.0 mΩμm 2 after correction of current distribution in device). Reader test results show that the low frequency track averaged output amplitude is 3.14 mV with the electrical SNR ¼28 dB. These read heads have the transition width of readback waveform T50 of 22 nm and the magnetic read track width of 35.6 nm. The obtained on-track bit error rate is close to 10 3 decade at a linear density of 1800 KFCI, potentially realizing a magnetic recording with an areal density of up to 800 Gb/in 2 . & 2013 Elsevier B.V. All rights reserved. 1. Introduction Current perpendicular to plane (CPP) giant magnetoresistance (GMR) reader technology has been extensively investigated in the last few years in response to the demand for increasing areal density in magnetic recording. With areal densities approaching 1.5 TB/in 2 , one alternative to MgO TMR that shows potential for next-generation sensor application is the all-metal CPP GMR device. Processing of the all metal CPP GMR sensors has been expedited recently through significant progress in the develop- ment of magnetic half metals and Heusler alloys [1–8]. Due to their characteristic low RA in the order of about 0.1 Ωμm 2 , the CPP GMR sensors provide potentially lower noise, improved bandwidth performance, and hence faster data transfer rate. To achieve a high areal density of magnetic recording, the required RA of sensors should be scaled down. The CPP GMR or ΔRA has to be significantly enhanced in order to provide sufficient signal to noise ratio (SNR) and to overcome the limitations imposed by the reliability and instability requirements. Ferromagnetic Heusler alloys such as Co 2 MnSi and other full Heusler variations show high spin polarization that might yield large CPP GMR in spin valves. Recent experiments in Heusler alloy based multilayer structures epitaxially-grown on MgO (001) sub- strates have shown the room temperature CPP GMR ratio of up to 29% (ΔRA ¼ 8.0 mΩμm 2 ) [4]. One of the co-authors showed that the CPP GMR can be as large as 75% in Heusler alloy based pseudo spin valves grown on MgO (001) substrates [7]. Nevertheless, achievement of large CPP GMR in such spin valve sensors signifi- cantly depends on the availability of highly ordered L2 1 /B2 crystalline structures for the Heusler alloy layers. Recent industrial efforts to fabricate Heusler alloy based CPP GMR readers on AlTiC substrates have yielded the CPP GMR of ΔRA¼ 2.0–4.0 mΩμm 2 and SNR¼ 29 dB for the finished readers [9–11]. Reader process becomes more complex where the Heusler alloy stacking has to be grown on the substrates or magnetic shield layers that are incompatible to the former in crystalline structure. Still there remain process chal- lenges for advanced sensor fabrication in terms of enhancement of output signal and reduction in noise and instability of devices with narrow shield-to-shield spacing (SSS). In this study, we investigated the CPP GMR in different magnetic CoFeMnSi (CFMS) Heusler alloy based spin valves. Film stacking design and its influence on the CPP GMR were studied by SpinFlow 3D™ modeling of spin dependent electron transport in Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jmmm Journal of Magnetism and Magnetic Materials 0304-8853/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jmmm.2013.12.050 n Corresponding author. Tel.: þ1 5106837658. E-mail address: zhitao.diao@wdc.com (Z. Diao). Journal of Magnetism and Magnetic Materials 356 (2014) 73–81