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Antiferromagnetic insulators are a ubiquitous class of magnetic materials, holding the promise of low-dissipation spin-based computing devices that can display ultra-fast switching and are robust against stray fields. However, their imperviousness to magnetic fields also makes them difficult to control in a reversible and scalable manner. Here we demonstrate a novel proof-of-principle ionic approach to control the spin reorientation (Morin) transition reversibly in the common antiferromagnetic insulator α-Fe2O3 (haematite) – now an emerging spintronic material that hosts topological antiferromagnetic spin-textures and long magnon-diffusion lengths. We use a low-temperature catalytic-spillover process involving the post-growth incorporation or removal of hydrogen from α-Fe2O3 thin films. Hydrogenation drives pronounced changes in its magnetic anisotropy, Néel vector orientation and canted magnetism via electron injection and local distortions. We explain these effects with a detailed magnetic anisotropy model and first-principles calculations. Tailoring our work for future applications, we demonstrate reversible control of the room-temperature spin-state by doping/expelling hydrogen in Rh-substituted α-Fe2O3. One major challenge for antiferromagnetic spintronics is how to control the antiferromagnetic state. Here Jani et al. demonstrate the reversible ionic control of the room-temperature magnetic anisotropy and spin reorientation transition in haematite, via the incorporation and removal of hydrogen. [ABSTRACT FROM AUTHOR]

Nanometer-sized noble metallic particles embedded in dielectric matrices are of wide interest. To exploit their plasmonic properties, efforts have been made to vary their size and shape by various methods during or after fabrication. Energetic ion irradiation has been found to be very useful in this objective. In the present work, we have studied the effect of inter-particle separation using atomistic simulations to gain a better understanding of the pathway in the modification of size of nanoparticles which are smaller than the ion track size in the matrix. It is found that the size of nanoparticles can be varied depending on the initial inter-particle separation and the temperature in the spike generated by the passed energetic ion. The results agree with the model proposed by our group, based on inter-particle separation, to explain experimental results on the swift heavy ion-induced modification of the size of embedded nanoparticles. [ABSTRACT FROM AUTHOR]