Search

We performed soft x-ray spectroscopic studies of the ferrimagnet ${\mathrm{TbFe}}_{5}{\mathrm{Al}}_{7}$ with strong easy-plane anisotropy in pulsed magnetic fields up to 29 T along with bulk magnetization and magnetostriction measurements. We observed pronounced amplitude changes of x-ray magnetic circular dichroism and x-ray absorption spectra at the field-induced magnetic transition. This microscopically evidences the simultaneous rotation of the Tb $4f$ and Fe $3d$ magnetic moments from a collinear ferrimagnetic order along the [100] axis to a state with the moments close to [010], the other easy-axis direction of the tetragonal lattice in magnetic fields applied along the [100] axis. We determined the magnetic-anisotropy constant of ${\mathrm{TbFe}}_{5}{\mathrm{Al}}_{7}$ by simulating the high-field macro- and microscopic magnetization process using a two-sublattice model.

We determined the crystal structure of ${\mathrm{Cs}}_{2}{\mathrm{LiRuCl}}_{6}$, which was synthesized in this work, and investigated its magnetic properties. ${\mathrm{Cs}}_{2}{\mathrm{LiRuCl}}_{6}$ has a hexagonal structure composed of linear chains of face-sharing ${\mathrm{RuCl}}_{6}$ and ${\mathrm{LiCl}}_{6}$ octahedra. In two thirds of the structural chains, ${\mathrm{Ru}}^{3+}$ and ${\mathrm{Li}}^{+}$ sites are almost ordered, while in the other chains their sites are disordered. This situation is analogous to the ground state of the antiferromagnetic Ising model on a triangular lattice. Using electron paramagnetic resonance, we evaluated the $g$ factors of ${\mathrm{Ru}}^{3+}$ with effective spin-$\frac{1}{2}$ as ${g}_{c}\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}2.72$ and ${g}_{ab}\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}1.50$ for magnetic fields $H$ parallel and perpendicular to the $c$ axis, respectively. Magnetization curves for $H\ensuremath{\parallel}c$ and $H\phantom{\rule{0.16em}{0ex}}\ensuremath{\perp}\phantom{\rule{0.16em}{0ex}}c$ are highly anisotropic. However, these magnetization curves approximately coincide when normalized by the $g$ factors. It was found from the magnetization and specific heat results that ${\mathrm{Cs}}_{2}{\mathrm{LiRuCl}}_{6}$ can be described as a coupled one-dimensional $S\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}1/2$ Heisenberg-like antiferromagnet with $J/{k}_{\mathrm{B}}\phantom{\rule{0.16em}{0ex}}\ensuremath{\simeq}\phantom{\rule{0.16em}{0ex}}3.7$ K. Three-dimensional ordering occurs at ${T}_{\mathrm{N}}\phantom{\rule{0.16em}{0ex}}=\phantom{\rule{0.16em}{0ex}}0.48$ K. A magnetic phase diagram for $H\ensuremath{\parallel}c$ is also presented.

The high-field magnetic properties and magnetic order of the gem mineral green dioptase Cu$_6[$Si$_6$O$_{18}]\cdot 6$H$_2$O have been studied by means of single-crystal neutron diffraction in magnetic fields up to $21~$T and magnetization measurements up to $30~$T. In zero field, the Cu$^{2+}$-moments in the antiferromagnetic chains are oriented along the $c$-axis with a small off-axis tilt. For a field applied parallel to the $c$-axis, the magnetization shows a spin-flop-like transition at $B^*=12.2~$T at $1.5~$K. Neutron diffraction experiments show a smooth behavior in the intensities of the magnetic reflections without any change in the periodicity of the magnetic structure. Bulk and microscopic observations are well described by a model of ferromagnetically coupled antiferromagnetic $XXZ$ spin-$\frac{1}{2}$ chains, taking into account a change of the local easy-axis direction. We demonstrate that the magnetic structure evolves smoothly from a deformed N\'eel state at low fields to a deformed spin-flop state in a high field via a strong crossover around $B^*$. The results are generalized for different values of interchain coupling and spin anisotropy., Comment: 12 pages, 12 figures

The low-temperature magnetic properties and magnetic structure of fully dehydrated black dioptase ${\mathrm{Cu}}_{6}{\mathrm{Si}}_{6}{\mathrm{O}}_{18}$ have been studied by single-crystal neutron diffraction and magnetization measurements in magnetic fields up to 30 T. The intrachain ${J}_{c}$ and interchain ${J}_{ab}$ interactions as well as the anisotropy of the exchange coupling ${J}_{c}$ have been determined using inelastic neutron-scattering techniques. Zero-field antiferromagnetic order at ${T}_{\mathrm{N}}=6.7$ K can be described by a commensurate propagation vector of $\mathbf{k}=(0,0,3/2)$ with respect to the hexagonal $R\overline{3}$:H unit cell. The Cu magnetic moments are aligned antiferromagnetically along the $c$ axis with about ${12}^{\ensuremath{\circ}}$ tilt and are coupled ferromagnetically between the chains. The high-field magnetization measurements provide strong evidence for the presence of a spin-flop phase above 8 T. We found that ${J}_{c}$ in black dioptase is significantly increased, while ${J}_{ab}$ is much weaker compared to its counterpart, green dioptase ${\mathrm{Cu}}_{6}[{\mathrm{Si}}_{6}{\mathrm{O}}_{18}] 6{\mathrm{H}}_{2}\mathrm{O}$. We suggest that black dioptase behaves like a nearly ideal $S=1/2$ antiferromagnetic Heisenberg spiral chain with enhanced quantum fluctuations and weak spinon confinement ${J}_{ab}/{J}_{c}\ensuremath{\sim}0.02$.

The dissolution of anhydrous iron bromide in a mixture of pyridine and acetonitrile, in the presence of an organic amine, results in the formation of an [Fe34] metal oxide molecule, structurally characterised by alternate layers of tetrahedral and octahedral FeIII ions connected by oxide and hydroxide ions. The outer shell of the complex is capped by a combination of pyridine molecules and bromide ions. Magnetic data, measured at temperatures as low as 0.4 K and fields up to 35 T, reveal competing antiferromagnetic exchange interactions; DFT calculations showing that the magnitudes of the coupling constants are highly dependent on both the Fe‐O‐Fe angles and Fe−O distances. The simplicity of the synthetic methodology, and the structural similarity between [Fe34], bulk iron oxides, previous FeIII–oxo cages, and polyoxometalates (POMs), hints that much larger molecular FeIII oxides can be made., E.K.B. thanks the EPSRC for funding (grants EP/N01331X/1 and EP/P025986/1). G.R. thanks UGC‐UKIERI grant number 184‐1/2018(lC) and SERB (CRG/2018/000430). S.D. thanks the UGC for an SRF fellowship. M.E. thanks MICINN (RTI2018‐094909‐J‐I00). J.S. thanks the Deutsche Forschungsgemeinschaft DFG (314331397 (SCHN 615/23‐1).