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.

No abstract

Controlled surface modification and nano-dots structures over Si(111) surfaces have been produced by oblique angle sputter deposition of 80 keV Ar + beam. Temporal parameters such as self-assemble, tunability of size and density of fabricated nano-dots exhibit distinct fluence dependence. Crystalline to amorphous (c/a) phase transition for sputter deposited Si(111) surfaces has been observed. RBS/C reveals the non-linear response of damage distribution with Ar ion fluence. Compositional alterations like degree of amorphization, damage distribution and depth profiling of Ar in these nano-structured surfaces has been correlated with the morphological and structural findings. The underlying self-organization mechanism relies in ion beam sputtering induced erosion and re-deposition of Si atoms thereby leading to mass transport inside the amorphous layers. Such nano-structured Si(111) surfaces could be applied as key engineering substrates for surface reconstruction, optoelectronic devices, data storage devices, recording media and photovoltaic applications.

The recovery effect of isochronal thermal annealing and inelastic energy deposited during 100 MeV Ag swift heavy ion (SHI) irradiation is demonstrated in the case of 4H-SiC pre-damaged by elastic energy deposition of 300 keV Ar ion. The Ar-induced fractional disorder follows a nonlinear two-step damage build-up. The fractional disorder level of 0.3 displacements per atom (dpa) is established as the threshold above which the lattice rapidly enters the amorphous phase, characterized by the presence of highly photo-absorbing defects. The SHI-induced recovery suggests that the damage annealing, in the pre-damaged region (∼350 nm) where the Se for 100 MeV Ag is almost constant (∼16.21 keV/nm), is more pronounced than the damage creation by SHI. This allows the disorder values to saturate at a lower value than the present initial disorder. Furthermore, the thermal effect due to SHI irradiation of an amorphous nano-zone embedded in a crystalline host matrix has been evaluated using the 3D implementation of the thermal spike. The recovery process by SHI is ascribed to the thermal spike-induced atomic movements resulting from the melting and the resolidification of the crystalline–amorphous interface.

No abstract