Multiferroic composite materials, consisting of coupled ferromagnetic and piezoelectric phases, are of great importance in the drive towards creating faster, smaller and more energy efficient devices for information and communications technologies. Such devices require thin ferromagnetic films with large magnetostriction and narrow microwave resonance linewidths. Both properties are often degraded, compared to bulk materials, due to structural imperfections and interface effects in the thin films. Here we present the development of cubic single crystal thin films of Galfenol (Fe₈₁Ga₁₉) grown by molecular beam epitaxy onto GaAs(001) substrates. We show that the thin films possess a magnetostriction as large as the best reported values for bulk single crystals. When incorporated into hybrid piezoelectric/ferromagnetic devices, this allows the magnetic anisotropy and microwave resonant frequency to be tuned by voltage-induced strain. Combined with the cubic magnetocrystalline anisotropy, this has enabled the demonstration of useful functionalities such as voltage induced non-volatile switching of the magnetisation direction [1] and the modification of ordered magnetic domain patterns [2].

The excellent magnetic properties of the single crystal thin films make them promising candidates for developing tunable devices for magnetic information storage, processing and  microwave communications.

[1] D.E. Parkes, et al., Non-volatile voltage control of magnetization and magnetic domain walls in magnetostrictive epitaxial thin films, Appl. Phys. Lett. 101, 072402 (2012).

[2] S.A. Cavill, et al., Electrical control of magnetic reversal processes in magnetostrictive structures, Appl. Phys. Lett. 102, 032405 (2013).

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1. From GaMnAs to CuMnAs: growth by Molecular Beam Epitaxy (MBE)