technical paper

MMM 2022

November 07, 2022

Minneapolis, United States

Enhanced Spin Signal in Metallic Non Local Spin Valves with Highly

Magnetic-tunnel-junction-based hard disk drive read-heads have been highly successful. They face pressing current challenges, however, due to high resistance-area product, which leads to impedance-mismatch-driven signal-to-noise issues as scaling continues 1. Alternative all-metal spintronic devices are thus of high interest, including spin accumulation sensors based on non-local spin valves (NLSVs) 2. Due to low output signals in such devices, and also for fundamental research, it is highly desired to improve the spin signal in metallic NLSVs. As this spin signal is essentially proportional to the square of the current spin polarization, α 3, we have explored integration of high-spin-polarization Co1-xFex alloy ferromagnetic injectors/detectors into NLSVs. Co1-xFex alloys are known to display a peak in α at x ≈ 0.25 and have been employed in other spintronic devices 4,5. Otherwise identical Al-based NLSVs were fabricated with either conventional Co or Co75Fe25 ferromagnetic injectors/detectors via single-shot ultrahigh vacuum evaporation into electron-beam-lithographic masks (Fig 1, inset). X-ray and spectroscopic characterization indicates site-disordered BCC Co75Fe25 films. Comparing Co75Fe25 and Co, the non-local spin signal (ΔRNL) increases by factors of 3 and 4, respectively, at 275 and 5 K (Fig. 1), confirming significant enhancement. Full analysis of the temperature and injector/detector separation dependence reveal α values of ~60%, with a strikingly weak temperature dependence (Fig. 2). We thus establish a facile route to ~2-fold enhancement of spin polarization over conventional ferromagnets used in NLSVs (Fig. 2), thereby inducing ~4-fold enhancement in spin signal, of interest for both applied and fundamental purposes. This work is supported by the NSF and the Advanced Storage Research Consortium.

References 1 T. Nakatani, Z. Gao, and K. Hono, MRS Bull., Vol. 43, p. 106 (2018) 2 H. Takagishi, K. Yamada, and H. Iwasaki, IEEE Trans. Mag., Vol. 46, p. 2086 (2010) 3 S. Takahashi, and S. Maekawa, PRB, Vol. 67(5), p. 052409 (2003) 4 D. J. Monsma, and S. S. P. Parkin. Appl. Phys. Lett., Vol. 77(5), p. 720 (2000) 5 S. V. Karthik, T. M. Nakatani, A. Rajanikanth, J. Appl. Phys., Vol. 105(7), p. 07C916 (2009)


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