${\mathrm{SmFeO}}_3$ has attracted considerable attention very recently due to its reported multiferroic properties above room temperature. We have performed powder and single crystal neutron diffraction as well as complementary polarization dependent soft X-ray absorption spectroscopy measurements on floating-zone grown ${\mathrm{SmFeO}}_3$ single crystals in order to determine its magnetic structure. We found a $k=0$ $G$-type collinear antiferromagnetic structure that is not compatible with inverse Dzyaloshinskii-Moriya interaction driven ferroelectricity. While the structural data reveal a clear sign for magneto-elastic coupling at the Néel-temperature of $\sim 675\mathrm{K}$, the dielectric measurements remain silent as far as ferroelectricity is concerned.

The condensation of magnetic quasiparticles into the nonmagnetic ground state has been used to explain novel magnetic ordering phenomena observed in quantum spin systems. We present neutron scattering results across the pressure-induced quantum phase transition and for the novel ordered phase of the magnetic insulator $\mathrm{T}\mathrm{l}\mathrm{C}\mathrm{u}{\mathrm{C}\mathrm{l}}_3$, which are consistent with the theoretically predicted two degenerate gapless Goldstone modes, similar to the low-energy spin excitations in the field-induced case. These novel experimental findings complete the field-induced Bose-Einstein condensate picture and support the recently proposed field-pressure phase diagram common for quantum spin systems with an energy gap of singlet-triplet nature.

Several oxy-apatite materials La_10−xSr_x(TO₄)₆O_3−0.5x (T = Ge, Si; 10−x = 9.00, 8.80, 8.65 and 8.00) and La_9.33(Si_1−xGe_xO₄)₆O₂ (x = 0, 0.5, 0.67) have been prepared as highly crystalline phases. The impedance study showed that all samples are oxide ion conductors. However, bulk conductivities changed by more than 2 orders of magnitude at a given temperature for some compositions. A thorough study on the oxygen sublattices for oxygen-stoichiometric oxy-apatites has been carried out. Constant-wavelength neutron powder diffraction data have been collected for La_9.33(SiO₄)₆O₂. Time-of-flight neutron data have been collected for La_9.33(Si_0.5Ge_0.5O₄)₆O₂, La₈Sr₂(SiO₄)₆O₂ and La₈Sr₂(GeO₄)₆O₂. The room-temperature structures have been derived from joint Rietveld refinements of neutron and laboratory X-ray powder diffraction data. High temperature structures have been obtained only from Rietveld refinements of neutron powder diffraction data. The refinements show that La_9.33(SiO₄)₆O₂ and La_9.33(Si_0.5Ge_0.5O₄)₆O₂ contain interstitial oxygen, associated to vacancies at the oxygen channels. The amount of interstitial oxygen is negligible in La₈Sr₂(SiO₄)₆O₂ and La₈Sr₂(GeO₄)₆O₂. Hence, the novelty of this work is to explain the high oxide conductivity of the lanthanum-deficient samples which it is due to the presence of interstitial oxygens. Lanthanum stoichiometric samples do not have interstitial oxygens and, so, their conductivities are much lower.