Over 50% reduction in the formation energy of Co-based Heusler alloy films by two-dimensional crystallisation

Abstract

Crystalline formation of high magnetic-moment thin films through low-temperature annealing processes compatible with current semiconductor technologies is crucial for the development of next generation devices, which can utilise the spin degree of freedom. Utilising in-situ aberration corrected electron microscopy, we report a 235 °C crystallisation process for a Co-based ternary Heusler-alloy film whose initial nucleation is initiated by as few as 27 unit cells. The crystallisation occurs preferentially in the ⟨111⟩ crystalline directions via a two-dimensional (2D) layer-by-layer growth mode; resulting in grains with [110] surface normal and [111] plane facets. This growth process was found to reduce the crystallisation energy by more than 50% when compared to bulk samples whilst still leading to the growth of highly ordered grains expected to give a high degree of spin-polarisation. Our findings suggest that the 2D layer-by-layer growth minimises the crystallisation energy allowing for the possible implementation of highly spin-polarised alloy films into current chip and memory technologies.

Heusler alloys for spintronic devices: review on recent development and future perspectives

“…This fact hinders the use of Heusler alloy films to be used in spintronic devices. Recently, layer-by-layer crystallisation has been reported along the Heusler alloy (110) plane to reduce the crystallisation energy, resulting in the annealing temperature, by over 50% [ 52 ]. A similar crystallisation process has been demonstrated at a higher temperature to uniformly crystallise the Heusler alloy films [ 53 ].…”

Perpendicular Magnetic Anisotropy in Heusler Alloy Films and Their Magnetoresistive Junctions

“…This prevents the Heusler alloys to be used in spintronic devices. Recently, layer-by-layer growth in the Heusler alloy (110) plane (see Figure 2b) has been reported to decrease the crystallisation energy, i.e., the annealing temperature, by over 50% [42]. A similar crystallisation process has been demonstrated at higher temperature to uniformly crystallise the Heusler-alloy films [43].…”

“…Temperature-dependent electrical resistivity measurements can also reveal the detailed scattering mechanism by defects in the films [52]. The half-metallicity can be determined by point-contact Andreev reflection (PCAR) [32] and infrared photoexcitation [42]. Additionally, X-ray magnetic circular dichroism (XMCD) with synchrotron radiation can reveal spin and orbital moments per constituent atoms [34].…”

Peter Swann’s Key Role in the Past, Present and Future of Dynamic In-situ TEM

“…At Oxford and DuPont [16] further progress was made in designing an integrated system to fit higher resolution modern instruments [10] and this is now used in commercial machines dedicated to the ETEM mode. The most recent equipment developed at York has 0.1nm image resolution in both ESTEM and ETEM and a full array of imaging and analytical methods [17,18,19]. The ESTEM uses redesigned Gatan hot stages and DENS MEMS technology.…”