The stability and physical properties of the tetragonal phase of bulk CuMnAs antiferromagnet

Abstract

The effect of Cu substitution on the stability of the CuMnAs tetragonal phase was studied both experimentally and by ab initio calculations. Polycrystalline samples with various compositions Cu1+xMn1-xAs (x = 0-0.5) were synthetized. The tetragonal phase of CuMnAs is found to be stabilized by substituting Mn by Cu in the amount of x ~ 0.1 or higher. This observation is supported by ab initio calculations of the total energy of the tetragonal and orthorhombic phases; with increasing Cu content the tetragonal phase is favoured. Small variations of composition thus allow to grow selectively one of these two phases with distinct and unique features for antiferromagnetic spintronics.Measurements of magnetic susceptibility and differential scanning calorimetry have shown that the tetragonal Cu1+xMn1-xAs has an antiferromagnetic behaviour with the maximum Néel temperature TN = 507 K for the highest Mn content samples, decreasing with the decreasing Mn content.

Antiferromagnetic CuMnAs: Ab initio description of finite temperature magnetism and resistivity

“…On the experimental side, we note that orthorhombic phase of CuMnAs exists, see Ref. [7] for a phase diagram. Here we focus on tetragonal CuMnAs, which is stabilised by growth on suitably chosen substrates.…”

“…Both geometry and lattice constants were taken from literature (structure "II" in Ref. [20]) and the same values are used for all compositions and temper- In a separate work [29], various types of chemical disorder are discussed in detail while here, we investigate only prototypical and reasonable [7] Cu Mn defect with Cu impurities on Mn sublattices. Concentrations of this impurity are stated per formula unit.…”

“…One of the those materials, which has been known [2] to be an antiferromagnet (AFM) since 1980's and has only recently been identified as a system with locally broken inversion symmetry [3] -a precondition for the observation of staggered spin-orbit torques [4], a novel means of manipulation of magnetic moments in AFMs -is CuMnAs in its tetragonal phase. Detailed understanding of its transport properties is desirable and, with the prospect of using it under conditions of industrial applications [5,6] allowed by its relatively high Néel temperature T N ≈ 490 K [6,7], effects of chemical and temperatureinduced disorder (phonons and magnons) should be included in the model.…”

Electrical transport properties of bulk tetragonal CuMnAs

“…In the bulk form, CuMnAs was originally reported to have orthorhombic structure 9 while thin films grown on GaP or GaAs substrates 10 grow in a tetragonal phase. Recent studies of off-stoichiometric Cu 1+x Mn 1−x As compounds 11 have shown 12,13 that their crystal structure is rather sensitive to the composition. While the stoichiometric CuMnAs compounds crystallise in an orthorhombic structure (Pnma), few percent of copper excess at the expense of Mn turns the structure to a tetragonal one (P4/nmm).…”

“…The two appendices focus on magnetic anisotropy of CuMnAs and its modelling and certain specialised aspects of micro- A sample of tetragonal CuMnAs was prepared by reaction of high purity copper, manganese and arsenic as previously reported. 13 Tetragonal P4/nmm structure was confirmed by powder x-ray diffraction at room temperature on Bruker D8 Advance diffractometer. 13 Composition analysis performed by energy-dispersive x-ray detector (EDX) suggests a slight prevalence of copper, the stoichiometry being 1.02(1):0.99(2):0.99 (2) for Cu:Mn:As; Néel temperature (T N ) is 507 K. From thus obtained polycrystal, a single-crystal grain was cleaved, oriented using x-ray diffraction and its orientation was further refined on an SEM stub holder using electron backscatter diffaction (EBSD).…”