Dipolar superferromagnetism with reentrant low-temperature superspin glass behavior is observed on a randomly distributed ferromagnetic nanoparticle systems in discontinuous metal-insulator multilayers $\left[{\mathrm{Co}}_{80}{\mathrm{Fe}}_{20}\mathrm{}\right(t)/{\mathrm{Al}}_2{\mathrm{O}}_3(3\mathrm{}\mathrm{}\mathrm{n}\mathrm{m}){]}_{10}$ with nominal thickness $1.1<~t<~1.3\mathrm{nm}$ by use of ac susceptometry and dc magnetometry. At $t=1.0\mathrm{}\mathrm{nm},$ superspin glass-like freezing is evidenced by the criticality of dynamic and nonlinear susceptibilities.

Dynamic microwave properties of arrays of circular $\mathrm{Ni}$ and ${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ dots were studied by $X$ -band ferromagnetic resonance $\left(\mathrm{FMR}\right)$ technique. All of the dots had the same radius $0.5\mu \mathrm{m}$ , thickness $50–70\mathrm{nm}$ , and were arranged into rectangular or square array with different interdot separations. In the case of perpendicular magnetization multiple (up to 8) sharp resonance peaks were observed below the main $\mathrm{FMR}$ peak, and the relative positions of these peaks were independent of the interdot separations. Quantitative description of the observed multiresonance $\mathrm{FMR}$ spectra is given using the dipole-exchange spin wave dispersion equation for a perpendicularly magnetized film where in-plane wave vector is quantized due to the finite dot radius, and the inhomogenetiy of the intradot static demagnetization field in the nonellipsoidal dot is taken into account.

We report on the discovery of an isothermal structural transition observed in Bi${}_{1-x}$La${}_x$FeO${}_3$ ($0.17⩽x⩽0.19$) ceramics. At room temperature, an initially pure polar rhombohedral phase gradually transforms into a pure antipolar orthorhombic one. The polar phase can be recovered by annealing at $T>300\hspace{0.5em}{}^{°}$C. In accordance with neutron powder diffraction data, an inverse isothermal antipolar-polar transition takes place at $T>300$ ${}^{°}$C, where the polar phase becomes more stable. The antipolar phase is characterized by a weak ferromagnetic state, whereas the polar phase has been obtained in a mixed antiferromagnet–weak ferromagnet state. The relatively low external pressure induces polar-antipolar transition, but there is no evidence of electric-field-driven antipolar-polar transition. The observed large local piezoelectric response is associated with structural instability of the polar phase, whereas local multistate piezoelectric loops can be related to the domain wall pinning effect.

Enhancement of Gilbert damping in polycrystalline cobalt thin-film multilayers of various thicknesses, overlayered with copper or iridium, was studied in order to understand the role of local interface structure in spin pumping. X-ray diffraction indicates that cobalt films less than 6 nm thick have strong fcc(111) texture while thicker films are dominated by hcp(0001) structure. The intrinsic damping for cobalt thicknesses above 6 nm is weakly dependent on cobalt thickness for both overlayer materials, and below 6 nm the iridium overlayers show higher damping enhancement compared to copper overlayers, as expected due to spin pumping. The interfacial spin mixing conductance is significantly enhanced in structures where both cobalt and iridium have fcc(111) structure in comparison to those where the cobalt layer has subtly different hcp(0001) texture at the interface.

Magnetic and structural characteristics of $\mathrm{Er}\mathrm{Fe}{\mathrm{O}}_3$ , $\mathrm{Tm}\mathrm{Fe}{\mathrm{O}}_3$ , and $\mathrm{Yb}\mathrm{Fe}{\mathrm{O}}_3$ single crystals were studied over a wide temperature range. Magnetic measurements found that the spin-rotation transitions in all crystals are well described by the earlier proposed theory with no fitting parameters. Additionally, they have shown the absence of the magnetic compensation point in $\mathrm{Tm}\mathrm{Fe}{\mathrm{O}}_3$ and a noticeable growth of the $c$ -axis magnetization at low temperatures in $\mathrm{Tm}\mathrm{Fe}{\mathrm{O}}_3$ and $\mathrm{Er}\mathrm{Fe}{\mathrm{O}}_3$ . The x-ray measurements found no symmetry-lowering lattice distortions during the reorientation. Overall, the measurements cover a wide range of material parameters and demonstrate the generality of the modified mean field theory of the ${\Gamma }_4\to {\Gamma }_{24}\to {\Gamma }_2$ orientation phase transitions in orthoferrites.

We report on linear spin dynamics in the vortex state of Permalloy cylindrical dots subjected to an in-plane bias magnetic field. We demonstrate experimentally by a broadband ferromagnetic resonance technique and by simulations that breaking the cylindrical symmetry of the magnetic vortex gradually changes and suppresses the azimuthal spin eigenmodes below the vortex nucleation field and leads further to the appearance of new eigenmodes. The parallel microwave field pumping is shown to be a unique tool to observe spin excitation modes localized near the strongly shifted vortex core for the bias field between the vortex nucleation and annihilation fields. Meanwhile, the perpendicular field pumping, which excites the spin waves throughout the entire dot, reveals a crossover between two dynamic vortex regimes near the nucleation field.