The properties of isolated chiral skyrmions in thin magnetic films

Axisymmetric solitonic states (chiral skyrmions) have been predicted theoretically more than two decades ago. However, until recently they have been observed in a form of skyrmionic condensates (hexagonal lattices and other mesophases). In this paper we report experimental and theoretical investigations of isolated chiral skyrmions discovered in PdFe/Ir(111) bilayers two years ago (Science 341 , 636 (2013)). The results of spin-polarized scanning tunneling microscopy analyzed within the continuum and discrete models provide a consistent description of isolated skyrmions in thin layers. The existence region of chiral skyrmions is restricted by strip-out instabilities at low fields and a collapse at high fields. We demonstrate that the same equations describe axisymmetric localized states in all condensed matter systems with broken mirror symmetry, and thus our findings establish basic properties of isolated skyrmions common for chiral liquid crystals, different classes of noncentrosymmetric magnets, ferroelectrics, and multiferroics.Comment: 12 pages, 12 figure

Ferrimagnetism in sputtered MnxCoGe thin films

Investigations into the magnetic properties of sputtered MnxCoGe films in the range 0.8 <= x <= 2.5 uncovered ferrimagnetic order, unlike the ferromagnetic order reported in bulk samples. These films formed hexagonal Ni2In-type structures in all measured compositions. While the Curie temperatures of the films are comparable to those of hexagonal bulk MnCoGe, here is a reduction in the magnetization of the MnxCoGe film relative to bulk MnCoGe, and a magnetization compensation point is observed in the x < 1 samples. To understand the behavior, we calculated the magnetic moments of Mn-antisite defects in MnCoGe with density-function theory calculations. Models constructed from the calculation suggest that films become ferrimagnetic due to the presence of Mn on the Co and Ge sites. In the x < 1 samples, these defects arose from the disorder in the films, whereas for x > 1, the excess Mn was driven onto the antisites and produced ferrimagnetic order.Comment: 8 pages, 7 figure

Simultaneous existence of two spin-wave modes in ultrathin Fe/GaAs(001) films studied by Brillouin Light Scattering: experiment and theory

A double-peaked structure was observed in the {\it in-situ} Brillouin Light Scattering (BLS) spectra of a 6 \AA$$ thick epitaxial Fe/GaAs(001) film for values of an external magnetic field $H$, applied along the hard in plane direction, lower than a critical value $H_c\simeq 0.9$ kOe. This experimental finding is theoretically interpreted in terms of a model which assumes a non-homogeneous magnetic ground state characterized by the presence of perperpendicular up/down stripe domains. For such a ground state, two spin-wave modes, namely an acoustic and an optic mode, can exist. Upon increasing the field the magnetization tilts in the film plane, and for $H \ge H_{c}$ the ground state is homogeneous, thus allowing the existence of just a single spin-wave mode. The frequencies of the two spin-wave modes were calculated and successfully compared with the experimental data. The field dependence of the intensities of the corresponding two peaks that are present in the BLS spectra was also estimated, providing further support to the above-mentioned interpretation.Comment: Shortened version (7 pages). Accepted for publication in Physical Review