The magnetic structure of the quasi-two-dimensional antiferromagnet ${\mathrm{NiPS}}_3$ has been determined by magnetometry and a variety of neutron diffraction techniques. The experiments show that the samples must be carefully handled, as gluing influences the magnetometry measurements while preferred orientation complicates the interpretation of powder diffraction measurements. Our global set of consistent measurements show numerous departures from previously published results. We show that the compound adopts a k = $\left[010\right]$ antiferromagnetic structure with the moment directions mostly along the $a$ axis, and that the paramagnetic susceptibility is isotropic. The critical behavior was also investigated through the temperature dependence of the magnetic Bragg peaks below the Néel temperature.

Neutron scattering from single crystals has been used to determine the magnetic structure and magnon dynamics of ${\text{FePS}}_3$, an $S=2$ Ising-like quasi-two-dimensional antiferromagnet with a honeycomb lattice. The magnetic structure has been confirmed to have a magnetic propagation vector of ${\mathbf{k}}_M=\left[01\frac{1}{2}\right]$ and the moments are collinear with the normal to the $ab$ planes. The magnon data could be modeled using a Heisenberg Hamiltonian with a single-ion anisotropy. Magnetic interactions up to the third in-plane nearest neighbor needed to be included for a suitable fit. The best fit parameters for the in-plane exchange interactions were $J_1=1.46, J_2=-0.04$, and $J_3=-0.96$ meV. The single-ion anisotropy is large, $\mathrm{\Delta }=2.66$ meV, explaining the Ising-like behavior of the magnetism in the compound. The interlayer exchange is very small, $J^{\prime }=-0.0073$ meV, proving that ${\text{FePS}}_3$ is a very good approximation to a two-dimensional magnet.

We report a study of the magnetization density in the mixed state of the unconventional superconductor ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$. On entering the superconducting state we find no change in the magnitude or distribution of the induced moment for a magnetic field of 1 T applied within the Ru ${\mathrm{O}}_2$ planes. Our results are consistent with a spin-triplet Cooper pairing with spins lying in the basal plane. This is in contrast with similar experiments performed on conventional and high- $T_c$ superconductors.

A new $\mathrm{N}\mathrm{H}\mathrm{\cdots }\mathrm{N}$ hydrogen-bonded ferroelectric crystal of $[{\mathrm{C}}_{\mathrm{6}}{\mathrm{H}}_{\mathrm{12}}{\mathrm{N}}_{\mathrm{2}}\mathrm{H}{\mathrm{]}}^{\mathrm{+}}\mathrm{R}\mathrm{e}{\mathrm{O}}_{\mathrm{4}}^{\mathrm{-}}$ ($\mathrm{d}\mathrm{a}\mathrm{b}\mathrm{c}\mathrm{o}\mathrm{H}\mathrm{R}\mathrm{e}{\mathrm{O}}_{\mathrm{4}}$) exhibits exceptional dielectric properties that result from the unique structure where all the bistable $\mathrm{N}\mathrm{H}\mathrm{\cdots }\mathrm{N}$ hydrogen bonds are parallel and directed exactly in the same sense. Consequently, the main structural origin of the spontaneous polarization of the crystal is the identical orientation of the asymmetric $\mathrm{N}{\mathrm{H}}^{\mathrm{+}}\mathrm{\cdots }\mathrm{N}$ hydrogen bonds along [001]. This first observation of a ferroelectric with parallel arrangement of the $\mathrm{N}{\mathrm{H}}^{\mathrm{+}}\mathrm{\cdots }\mathrm{N}$ bonded aggregates, gives temperature-independent and the highest spontaneous polarization ever reported for an organic or water-soluble substance.

The magnetic ordering structure of ${\mathrm{GdPO}}_4$ is determined at $T=60$ mK by the diffraction of hot neutrons with wavelength $\lambda =0.4696$ Å. It corresponds to a noncollinear antiferromagnetic arrangement of the Gd moments with propagation vector $\mathbf{k}=(1/2,0,1/2)$. This arrangement is found to minimize the dipole-dipole interaction and the crystal-field anisotropy energy, the magnetic superexchange being much smaller. The intensity of the magnetic reflections decreases with increasing temperature and vanishes at $T\approx 0.8$ K, in agreement with the magnetic ordering temperature $T_N=0.77$ K, as reported in previous works based on heat capacity and magnetic susceptibility measurements. The magnetocaloric parameters have been determined from heat capacity data at constant applied fields up to 7 T, as well as from isothermal magnetization data. The magnetocaloric effect, for a field change $\Delta B=0-7\mathrm{T}$, reaches $-\Delta S_T=375.8\mathrm{mJ}/{\mathrm{cm}}^3{\mathrm{K}}^{-1}$ at $T=2.1$ K, largely exceeding the maximum values reported to date for Gd-based magnetic refrigerants.