Neutron powder diffraction and inelastic measurements were performed examining the 5d pyrochlore Y2Ir2O7. Temperature dependent measurements were performed between 3.4 K and 290 K, spanning the magnetic transition at 155 K. No sign of any structural or disorder induced phase transition was observed over the entire temperature range. In addition, no sign of magnetic longrange order was observed to within the sensitivity of the instrumentation. These measurements do not rule out long range magnetic order, but the neutron powder diffraction structural refinements do put an upper bound for the ordered iridium moment of ∼ 0.2 µB/Ir (for a magnetic structure with wave vector Q = 0) or ∼ 0.5 µB/Ir (for Q = 0).

AAg 2 M[VO 4 ] 2 with A = Sr 2+ or Ba 2+ present a series of layered compounds featuring a triangular lattice of transition metal cations, M = Co 2+ or Ni 2+ , connected via nonmagnetic ortho-vanadates, which provide the magnetic superexchange within the layers. For this series of insulating compounds, ferromagnetic long-range order below 10 K is suggested by magnetization and specific heat measurements and confirmed by neutron diffraction experiments. We have investigated the impact of the spacer size of A 2+ separating the layers leading to a tilting of the vanadates and consequently inducing a change in the effective magnetic correlations. Magnetization and specific heat measurements corroborate the important dependence of the magnetic superexchange on the orientation of the vanadates and the respective spin system. Furthermore, the ground state properties of the spin systems, S = 1 (Ni 2+ ) and S = 3/2 (Co 2+ ) in their respective octahedral coordination of oxygen, are evaluated. Calculated magnetic moments of the single ion complexes agree well with the magnetic structure. We, furthermore, report the dependence of T c on applied isotropic pressure suggestive of a pressure effect on the effective ferromagnetic exchange coupling constants. In addition spectroscopic investigations probing the electronic structure of the [MO 6 ] complexes and the vibrational structure of the [VO 4 ] units are given.

AAg 2 Fe [VO 4 ] 2 with A = K or Rb was synthesized by solid state methods and characterized by thermodynamic properties measurements (Neél order at T N ≈ 3.0 K). The respective nuclear (a K,Rb = 5.48 Å, c K = 7.212 Å, c Rb = 7.357 Å, P3̅ , Z = 1) and magnetic structures were refined using neutron diffraction in applied magnetic fields. The results indicate enhanced structural stability of the P3̅ structure and the realization of a frustrated triangular lattice with antiferromagnetic XY-anisotropies. Two magnetic structures were identified: a helical and chiral Y-phase with a propagation vector of (1/3, 1/3, ≈ 0.39) and a commensurate up−up−down phase. These unique compounds offer convenient experimental access for optimizing the features and properties of ferroaxial multiferroic materials.

We studied the magnetic properties of the garnet Co 3 Al 2 Si 3 O 12 synthesized under 5.5 GPa and 1250 °C by means of dc magnetic susceptibility, neutron powder diffraction, and specific heat. Although the magnetic Co 2+ ions form a geometrically frustrated hyper-Kagome lattice, we find that Co 3 Al 2 Si 3 O 12 exhibits a long-range antiferromagnetic order below T N = 11 K without showing magnetic frustration, i.e. the frustration index f ≡ |θ CW /T N | is close to unity. Refinements from neutron diffraction data show that Co 3 Al 2 Si 3 O 12 forms a complex antiferromagnetic structure characterized by the coexistence of collinear and commensurate spiral magnetic ordering of Co 2+ sublattices. Magnetic field induced spin-flop transition at μ 0 H c ≈ 4 T was also observed below T N .