The skyrmion lattice state (SkL), a crystal built of mesoscopic spin vortices, gains its stability via thermal fluctuations in all bulk skyrmion host materials known to date. Therefore, its existence is limited to a narrow temperature region below the paramagnetic state. This stability range can drastically increase in systems with restricted geometries, such as thin films, interfaces and nanowires. Thermal quenching can also promote the SkL as a metastable state over extended temperature ranges. Here, we demonstrate more generally that a proper choice of material parameters alone guarantees the thermodynamic stability of the SkL over the full temperature range below the paramagnetic state down to zero kelvin. We found that GaV4Se8, a polar magnet with easy-plane anisotropy, hosts a robust Néel-type SkL even in its ground state. Our supporting theory confirms that polar magnets with weak uniaxial anisotropy are ideal candidates to realize SkLs with wide stability ranges.
We report on magnetic resonance studies within the magnetically ordered phase of the quasi-one-dimensional antiferromagnet $\mathrm{Li}\mathrm{Cu}\mathrm{V}{\mathrm{O}}_{4}$. Our studies reveal a spin reorientational transition at a magnetic field ${H}_{c1}\ensuremath{\approx}25\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$ applied within the crystallographic ab plane in addition to the recently observed one at ${H}_{c2}\ensuremath{\approx}75\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$ [M. G. Banks et al., J. Phys.: Condens. Matter 19, 145227 (2007)]. Spectra of the antiferromagnetic resonance along low-frequency branches can be described in the framework of a macroscopic theory of exchange-rigid planar magnetic structures. These data allow us to obtain the parameter of the anisotropy of the exchange susceptibility together with a constant of the uniaxial anisotropy. Spectra of $^{7}\mathrm{Li}$ nuclear magnetic resonance (NMR) show that, within the magnetically ordered phase of $\mathrm{Li}\mathrm{Cu}\mathrm{V}{\mathrm{O}}_{4}$ in the low-field range $H<{H}_{c1}$, a planar spiral spin structure is realized with the spins lying in the ab plane, in agreement with neutron-scattering studies of Gibson et al. [Physica B 350, 253 (2004)]. Based on NMR spectra simulations, the transition at ${H}_{c1}$ can well be described as a spin-flop transition, where the spin plane of the magnetically ordered structure rotates to be perpendicular to the direction of the applied magnetic field. For $H>{H}_{c2}\ensuremath{\approx}75\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$, our NMR spectra simulations show that the magnetically ordered structure exhibits a modulation of the spin projections along the direction of the applied magnetic field $H$.
LaTiO$_3$ is known as Mott-insulator which orders antiferromagnetically at $T_{\rm N}=146$ K. We report on results of thermal expansion and temperature dependent x-ray diffraction together with measurements of the heat capacity, electrical transport measurements, and optical spectroscopy in untwinned single crystals. At $T_{\rm N}$ significant structural changes appear, which are volume conserving. Concomitant anomalies are also observed in the dc-resistivity, in bulk modulus, and optical reflectivity spectra. We interpret these experimental observations as evidence of orbital order.
The temperature dependence of the electron-spin resonance in ${\mathrm{La}}_{0.95}{\mathrm{Sr}}_{0.05}{\mathrm{MnO}}_{3}$ has been investigated and analyzed in the paramagnetic regime across the orbital ordering transition. From the temperature dependence and the anisotropy of linewidth and g value the orbital order can be unambiguously determined via the mixing angle of the wave functions of the ${e}_{\mathrm{g}}$ doublet. The linewidth shows a similar evolution with temperature as resonant x-ray scattering results.
