Polar magneto-optical Kerr effect in antiferromagnetic M2_2As (M=Cr, Mn, Fe) under an external magnetic field

Antiferromagnetic metals attract tremendous interest for memory applications due to their expected fast response dynamics in the terahertz frequency regime. Reading from and writing information into these materials is not easily achievable using magnetic fields, due to weak high-order magneto-optical signals and robustness of the magnetic structure against external magnetic fields. Polarized electromagnetic radiation is a promising alternative for probing their response, however, when ideal antiferromagnetic symmetry is present, this response vanishes. Hence, in this work we combine first-principles simulations with measurements of the polar magneto-optical Kerr effect under external magnetic fields, to study magneto-optical response of antiferromagnetic M$_2$As (M=Cr, Mn, and Fe). We devise a computational scheme to compute the magnetic susceptibility from total-energy changes using constraints on magnetic-moment tilting. Our predictions of the spectral dependence of polar magneto-optical Kerr rotation and ellipticity allow us to attribute these effects to breaking of the magnetic symmetry. We show that tilting affects the exchange interaction, while the spin-orbit interaction remains unaffected as the tilting angle changes. Our work provides understanding of the polar magneto-optical Kerr effect on a band structure level and underscores the importance of the magnetic susceptibility when searching for materials with large magneto-optical response.Comment: 9 pages, 9 figure

Wideband luminescence from bandgap-matched Mg-based Si core-shell geometry nanocomposite

We use wet treatment to integrate red-luminescent Si nanoparticles with Mg-based wide-bandgap insulators Mg(OH) and MgO (5.7 and 7.3 eV respectively). In the process, Mg2+ is reduced on Si nanoparticle clusters, while suffering combustion in water, producing a spatially inhomogeneous Mg(OH)2/MgO-Si nanoparticle composite with an inner material predominantly made of Si, and a coating consisting predominantly of magnesium and oxygen (“core-shell” geometry). The nanocomposite exhibit luminescence covering nearly entire visible range. Results are consistent with formation of Mg(OH)2/MgO phase with direct 3.43-eV bandgap matching that of Si, with in-gap blue-green emitting states of charged Mg and O vacancies. Bandgap match with nanocomposite architecture affords strong enough coupling for the materials to nearly act as a single hybrid material with novel luminescence for photonic and photovoltaic applications