Supercell Altermagnets

Altermagnets are compensated magnets with unconvetional $d$, $g$ and $i$-wave spin-channel order in reciprocal space. So far the search for new altermagnetic candidates has been focused on materials in which the magnetic unit cell is identical to the non-magnetic one, i.e. magnetic structures with zero propagation vector. Here, we substantially broaden the family of altermagnetic candidates by predicting supercell altermagnets. Their magnetic unit cell is constructed by enlarging the paramagnetic primitive unit cell, resulting in a non-zero propagation vector for the magnetic structure. This connection of the magnetic configuration to the ordering of sublattices gives an extra degree of freedom to supercell altermagnets, which can allow for the control over the order parameter spatial orientation. We identify realistic candidates MnSe$_2$ with a $d$-wave order, and RbCoBr$_3$, CsCoCr$_3$, and BaMnO$_3$ with $g$-wave order. We demonstrate the reorientation of the order parameter in MnSe$_2$, which has two different magnetic configurations, whose energy difference is only 5 meV, opening the possibility of controlling the orientation of the altermagnetic order parameter by external perturbations.Comment: 10 pages, 4 figure

Strain control of band topology and surface states in antiferromagnetic EuCd2_2As2_2

Topological semimetal antiferromagnets provide a rich source of exotic topological states which can be controlled by manipulating the orientation of the N\'eel vector, or by modulating the lattice parameters through strain. We investigate via ${ab\ initio}$ density functional theory calculations, the effects of shear strain on the bulk and surface states n two antiferromagnetic EuCd$_2$As$_2$ phases with out-of-plane and in-plane spin configurations. When magnetic moments are along the $\textit{c}$-axis, a $3\%$ longitudinal or diagonal shear strain can tune the Dirac semimetal phase to an axion insulator phase, characterized by the parity-based invariant $\eta_{4I} = 2$. For an in-plane magnetic order, the axion insulator phase remains robust under all shear strains. We further find that for both magnetic orders, the bulk gap increases and a surface gap opens on the (001) surface up to 16 meV. Because of a nonzero $\eta_{4I}$ index and gapped states on the (001) surface, hinge modes are expected to happen on the side surface states between those gapped surface states. This result can provide a valuable insight in the realization of the long-sought axion states.Comment: 5 pages, 4 figure

Ultrafast domain wall propagation due to the interfacial Dzyaloshinskii-Moriya interaction

It is shown that the interplay between curvature and interfacial Dzyalonshinsky-Moriya interaction (DMI) is a pathway to ultrafast domain wall (DW) dynamics in ferromagnetic nanotubes. In this work, we theoretically study the effect that interfacial DMI has on the average velocity of a vortex DW in thin ferromagnetic nanotubes grown around a core composed of heavy atoms. Our main result shows that by delaying the Walker breakdown instability, the DW average velocity is of the order of 10(3) m s(-1), which is greater than usual values for these systems. The remarkable velocities achieved through this configuration could greatly benefit the development of spintronic devices.Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT), CONICYT FONDECYT: 1161018, 1190324, 3180416. Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT), CONICYT PIA/BASAL: FB 0807

Topological magnonics in the two-dimensional van der Waals magnet CrI3

We report on the magnon spectrum of Kitaev-Heisenberg magnets and extract the parameters to model a two-dimensional CrI3. Our minimal spin Hamiltonian includes a contribution stemming from a Heisenberg, isotropic exchange, and a contribution arising from a Kitaev interaction, anisotropic and frustrated exchange. Our calculations reveal a gap that opens at the K and K' points and the topological nature of the magnons which lead to the thermal Hall effect. Furthermore, we calculate the magnon spectrum of nanoribbons illustrating the corresponding edge states.Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) CONICYT FONDECYT 1190324 Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) CONICYT FONDECYT 3190264 Comision Nacional de Investigacion Cientifica y Tecnologica (CONICYT) CONICYT PIA/BASAL AFB180001 Abdus Salam International Center for Theoretical Physics through the Simons Foundatio