Effect of Gas Composition During Pt Sputtering on Structural and Magnetic Properties of CoFeB Thin Films

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Abstract
Ultrathin Ta/CoFeB/Pt trilayer structures are relevant to a wide range of spintronic applications, from magnetic tunnel junctions to skyrmionics devices. Controlling the perpendicular magnetic anisotropy, Gilbert damping and Dzyaloshinskii-Moriya interaction in the CoFeB layer is key for these applications. We examine the role of sputter gas composition during the Pt overlayer deposition of a Ta/CoFeB/Pt trilayer in Ar, Kr and Xe working gas environments during direct current magnetron sputtering. Decreasing density of the Pt layer (from 21 g/cm 3 to 15 g/cm 3 ) was apparent in specular x-ray reflectivity measurements of the trilayer films when increasing the molecular weight of the sputtering gas from Ar to Kr to Xe. Significant effects on the Gilbert damping and the interfacial Dzyaloshinskii-Moriya interaction (DMI) energy were observed, with increases in the damping from 0.037(1) to 0.042(1) to 0.048(1), and reductions in the interfacial DMI from 0.47(4) mJ/m 2 to 0.45(5) mJ/m 2 to 0.39(4) mJ/m 2 . The ability to control the perpendicular magnetization and DMI strength of these materials through judicious interfacial control is a means toward magnetic devices with better stability at smaller lateral dimension, key to device scaling for spintronic device arrays.

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