Abstract
Ferroic materials (ferromagnetic, ferroelectric, ferroelastic) usually divide into domains with different orientations of their order parameter. Coupling between different ferroic systems creates new functionalities, for instance the electrical control of macroscopic magnetic properties including magnetization and coercive field. Here we show that ferroelastic domains can be used to control both magnetic order and magnetization direction at the nanoscale with a voltage. We use element-specific X-ray imaging to map the magnetic domains as a function of temperature and voltage in epitaxial FeRh on ferroelastic BaTiO3. Exploiting the nanoscale phase-separation of FeRh, we locally interconvert between ferromagnetic and antiferromagnetic states with a small electric field just above room temperature. Imaging and ab initio calculations show the antiferromagnetic phase of FeRh is favoured by compressive strain on c-oriented BaTiO3 domains, and the resultant magnetoelectric coupling is larger and more reversible than previously reported from macroscopic measurements. Our results emphasize the importance of nanoscale ferroic domain structure and the promise of first-order transition materials to achieve enhanced coupling in artificial multiferroics.
Highlights
We use magnetic imaging by photoelectron emission microscopy with X-ray excitation (XPEEM) and X-ray magnetic circular dichroism (XMCD) contrast to reveal that the ME effect in FeRh on BTO is driven by the creation and annihilation of the same ferromagnetic regions, due to coupling to ~10 μm-wide BTO ferroelastic domains
If no external electric field is applied, the T-BTO divides into ferroelastic domains separated by 90° walls, each subdivided into non-ferroelastic ferroelectric domains separated by 180° walls[19]
Blue regions with positive XMCD are unequivocally identified as FM phase regions whose in-plane magnetization component lies parallel to the incoming X-rays
Summary
We use magnetic imaging by photoelectron emission microscopy with X-ray excitation (XPEEM) and X-ray magnetic circular dichroism (XMCD) contrast to reveal that the ME effect in FeRh on BTO is driven by the creation and annihilation of the same ferromagnetic regions, due to coupling to ~10 μm-wide BTO ferroelastic domains. FeRh grows with the ordered body-centred cubic (bcc) CsCl-type structure, and is unstrained but highly aligned, with [100]FeRh || [110]BTO and [001]FeRh || [001]BTO. On cooling, both components undergo non-diffusive first-order phase transitions. On C-BTO [Fig. 1(c)], FM-FeRh experiences only a small biaxial strain from thermal expansion mismatch [−0.2% on cooling from the deposition temperature of 903 K to the BTO TC of 400 K]21,22. As the greater compressive strain of c-domains shifts the AF-FM transition to higher temperatures [Fig. 1(f)], large ME effects [Fig. 1(g)] are expected if we first heat (cool) from low (high) temperature on BTO consisting of c-domains (a-domains), and transform isothermally towards a-domains (c-domains) by changing the voltage across BTO
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