Complex magnetic structure of clusters and chains of Ni and Fe on Pt(111)

Correlation of Interface Interdiffusion and Skyrmionic Phases

Magnetic skyrmions are prime candidates for the next generation of spintronic devices. Skyrmions and other topological magnetic structures are known to be stabilized by the Dzyaloshinskii-Moriya interaction (DMI) that occurs when the inversion symmetry is broken in thin films. Here, we show by first-principles calculations and atomistic spin dynamics simulations that metastable skyrmionic states can also be found in nominally symmetric multilayered systems. We demonstrate that this is correlated with the large enhancement of the DMI strength due to the presence of local defects. In particular, we find that metastable skyrmions can occur in Pd/Co/Pd multilayers without external magnetic fields and can be stable even near room temperature conditions. Our theoretical findings corroborate with magnetic force microscopy images and X-ray magnetic circular dichroism measurements and highlight the possibility of tuning the intensity of DMI by using interdiffusion at thin film interfaces.

Magnonic contribution in thermal conductance of a nanostructure in the presence of magnon-phonon interaction

Using Green's function method, we study thermal transport properties of magnons transmitting through a magnetic nanowire at a certain temperature. In a small part of the nanowire in the middle, we are supposed to have two types of local and nonlocal magnon-phonon interactions. The self-energies for this part due to the other parts of the wire are analytically derived. First, we calculate the phonon mode-dependent magnon transmission coefficient in the classical canonical ensemble. Then, by taking an average of the phonon modes, we obtain the total magnon transmission coefficient and use it for computing magnon thermal conductance. We use the model to investigate four configurations of magnetic nanowires composed of ferromagnetic and/or antiferromagnetic parts. The results show that, when the scattering region has an antiferromagnetic alignment, the magnons transfer in the structure more weakly than for ferromagnetic alignment. There is a phonon-assisted mechanism for tunneling of magnons which are transmitted through the gap or between magnon quasifrequencies of the scattering region. Generally, in the same values for local and nonlocal strengths of magnon-phonon interaction, the nonlocal one has a greater effect on the magnonic thermal transport properties. We found the fitting functions in order to relate the macroscopic quantities of the magnon transmission coefficient and thermal conductivity to microscopic parameters of the strengths of the local and nonlocal magnon-phonon interaction.

First-principles Dzyaloshinskii-Moriya interaction in a non-collinear framework

We have derived an expression of the Dzyaloshinskii–Moriya interaction (DMI), where all the three components of the DMI vector can be calculated independently, for a general, non-collinear magnetic configuration. The formalism is implemented in a real space—linear muffin-tin orbital—atomic sphere approximation (RS-LMTO-ASA) method. We have chosen the Cr triangular trimer on Au(111) and Mn triangular trimers on Ag(111) and Au(111) surfaces as numerical examples. The results show that the DMI (module and direction) is drastically different between collinear and non-collinear states. Based on the relation between the spin and charge currents flowing in the system and their coupling to the non-collinear magnetic configuration of the triangular trimer, we demonstrate that the DMI interaction can be significant, even in the absence of spin-orbit coupling. This is shown to emanate from the non-collinear magnetic structure, that can induce significant spin and charge currents even with spin-orbit coupling is ignored.

β-tungsten: a promising metal for spintronics

Ultrathin films of β-tungsten provide very promising substrates for applications in spintronics, and the possibility of incorporating them into multilayers extends such expectations. Our calculations indicate that it is viable to deposit a single layer of Mn on two non-equivalent (0 0 1) surfaces of β-tungsten that have easy axes along orthogonal directions [0 1 0] and [1 0 0], respectively. The ferromagnetic structure of this Mn monolayer adsorbed to either of those surfaces displays a giant in-plane magneto-crystalline anisotropy that exceeds 12 meV per Mn atom. Furthermore, when coated with additional layers of β-tungsten the magnetization easy axis becomes perpendicular to the planes. We envisage that magnetic multilayers involving mono-crystalline thin films of β-tungsten oriented along high-symmetry directions offer a very fruitful playground for spintronic applications.

First-principles theory of electronic structure and magnetism of Cr nano-islands on Pd(1 1 1)

We report on the electronic structure, magnetic moments and exchange interactions of one- and two-dimensional Cr clusters on a Pd(1 1 1) substrate, using a real-space method based on density functional theory in the local spin density approximation. We find in general that for the investigated clusters, the magnetic moments are sizeable and almost entirely of spin-character. We demonstrate that the interactions in general are dominated by nearest-neighbor antiferromagnetic Heisenberg form, which implies that Cr on Pd(1 1 1) forms an ideal model system, in which clusters of almost any shape and size can be investigated from a Heisenberg Hamiltonian, using a nearest-neighbor exchange model. We have also found that complex magnetic structures can be realized for linear chains of Cr, due to a competition between exchange interaction and a weaker Dzyaloshinskii-Moriya interaction.

Non-collinear magnetism induced by frustration in transition-metal nanostructures deposited on surfaces

How does magnetism behave when the physical dimension is reduced to the size of nanostructures? The multiplicity of magnetic states in these systems can be very rich, in that their properties depend on the atomic species, the cluster size, shape and symmetry or choice of the substrate. Small variations of the cluster parameters may change the properties dramatically. Research in this field has gained much by the many novel experimental methods and techniques exhibiting atomic resolution. Here we review the ab-initio approach, focusing on recent calculations on magnetic frustration and occurrence of non-collinear magnetism in antiferromagnetic nanostructures deposited on surfaces.