Abstract
Heusler alloys are a large family of compounds with complex and tunable magnetic properties, intimately connected to the atomic scale ordering of their constituent elements. We show that using a chemical templating technique of atomically ordered X′Z′ (X′ = Co; Z′ = Al, Ga, Ge, Sn) underlayers, we can achieve near bulk-like magnetic properties in tetragonally distorted Heusler films, even at room temperature. Excellent perpendicular magnetic anisotropy is found in ferrimagnetic X3Z (X = Mn; Z = Ge, Sn, Sb) films, just 1 or 2 unit-cells thick. Racetracks formed from these films sustain current-induced domain wall motion with velocities of more than 120 m s−1, at current densities up to six times lower than conventional ferromagnetic materials. We find evidence for a significant bulk chiral Dzyaloshinskii–Moriya exchange interaction, whose field strength can be systematically tuned by an order of magnitude. Our work is an important step towards practical applications of Heusler compounds for spintronic technologies.
Highlights
Heusler alloys are a large family of compounds with complex and tunable magnetic properties, intimately connected to the atomic scale ordering of their constituent elements
We have introduced a universal concept of a chemical templating layers (CTLs) that enables the growth of complex Heusler compounds that demonstrate near bulk-like properties for films as thin as a single unit cell
The CTL can be chosen from a wide range of binary compounds that are formed from a transition metal and a main group element that are chemically ordered layer by layer
Summary
Heusler alloys are a large family of compounds with complex and tunable magnetic properties, intimately connected to the atomic scale ordering of their constituent elements. We note that it is more difficult to achieve atomic ordering in compounds with metallic bonding than, for example, in compound semiconductors or complex oxides where a variety of thin film growth techniques have been used to grow beautifully ordered materials[12,13,14,15] Another advantage of the Heusler materials studied here is that they are ferrimagnetic with low magnetization and, exhibit very narrow DWs that we estimate are as narrow as 1 unit cell. The most extensively studied tetragonal Heusler compounds are Mn3Ga and Mn3Ge because they display very high uniaxial magnetic anisotropy in their bulk form and very large PMA in thin films for which the c-axis is oriented perpendicular to the film[8,18,19,20,21,22] To obtain these properties, chemical ordering of the elements within the Heusler is essential.
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