Two-spinon and orbital excitations of the spin-Peierls system TiOCl

Magnetic Properties of Quasi-One-Dimensional Lanthanide Calcium Oxyborates Ca4LnO(BO3)3

This study examines the lanthanide calcium oxyborates Ca₄LnO(BO₃)₃ (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Yb). The reported monoclinic structure (space group Cm) was confirmed using powder X-ray diffraction. The magnetic Ln³⁺ ions are situated in well-separated chains parallel to the c axis in a quasi-one-dimensional array. Here we report the first bulk magnetic characterization of Ca₄LnO(BO₃)₃ using magnetic susceptibility χ(T) and isothermal magnetization M(H) measurements at T ≥ 2 K. With the sole exception of Ca₄TbO(BO₃)₃, which displays a transition at T = 3.6 K, no magnetic transitions occur above 2 K, and Curie–Weiss analysis indicates antiferromagnetic nearest-neighbor interactions for all samples. Calculation of the magnetic entropy change ΔS_m indicates that Ca₄GdO(BO₃)₃ and Ca₄HoO(BO₃)₃ are viable magnetocaloric materials at liquid helium temperatures in the high-field and low-field regimes, respectively.

The monoclinic lanthanide calcium oxyborates Ca₄LnO(BO₃)₃ contain well-separated chains of magnetic Ln³⁺ ions. Bulk magnetic characterization suggests quasi-one-dimensional behavior with no magnetic ordering above 2 K except in Ca₄TbO(BO₃)₃ (T_tr = 3.6 K). Ca₄GdO(BO₃)₃ and Ca₄HoO(BO₃)₃ are viable magnetocaloric materials at liquid helium temperatures in the high-field and low-field regimes, respectively.

The role of magnetic order in VOCl

VOCl and other transition metal oxychlorides are candidate materials for next-generation rechargeable batteries. We have investigated the influence of the underlying magnetic order on the crystallographic and electronic structure by means of density functional theory. Our study shows that antiferromagnetic ordering explains the observed low-temperature monoclinic distortion of the lattice, which leads to a decreased distance between antiferromagnetically coupled V-V nearest neighbors. We also show that the existence of a local magnetic moment removes the previously suggested degeneracy of the occupied levels, in agreement with experiments. To describe the electronic structure, it turns out crucial to take the correct magnetic ordering into account, especially at elevated temperature.

Probing multi-spinon excitations outside of the two-spinon continuum in the antiferromagnetic spin chain cuprate Sr2CuO3

One-dimensional (1D) magnetic insulators have attracted significant interest as a platform for studying quasiparticle fractionalization, quantum criticality, and emergent phenomena. The spin-1/2 Heisenberg chain with antiferromagnetic nearest neighbour interactions is an important reference system; its elementary magnetic excitations are spin-1/2 quasiparticles called spinons that are created in even numbers. However, while the excitation continuum associated with two-spinon states is routinely observed, the study of four-spinon and higher multi-spinon states is an open area of research. Here we show that four-spinon excitations can be accessed directly in Sr2CuO3 using resonant inelastic x-ray scattering (RIXS) in a region of phase space clearly separated from the two-spinon continuum. Our finding is made possible by the fundamental differences in the correlation function probed by RIXS in comparison to other probes. This advance holds promise as a tool in the search for novel quantum states and quantum spin liquids.

Indirect K-edge bimagnon resonant inelastic x-ray scattering spectrum of α-FeTe

We calculate the K-edge indirect bimagnon resonant inelastic x-ray scattering (RIXS) intensity spectra of the bicollinear antiferromagnetic order known to occur in the α-FeTe chalcogenide system. Utilizing linear spin wave theory for this large-S spin system we find that the bimagnon spectrum contains four scattering channels (two intraband and two interband). We find from our calculations that for suitable energy-momentum combination the RIXS spectra can exhibit a one-, two- or three- peak structure. The number of peaks provides a clue on the various bimagnon excitation processes that can be supported both in and within the acoustic and optical magnon branches of the bicollinear antiferromagnet. Unlike the RIXS response of the antiferromagnetic or the collinear antiferromagnetic spin ordering, the RIXS intensity spectrum of the bicollinear antiferromagnet does not vanish at the magnetic ordering wave vector [Formula: see text]. It is also sensitive to next-next nearest neighbor and biquadratic coupling interactions. Our predicted RIXS spectrum can be utilized to understand the role of multi-channel bimagnon spin excitations present in the α-FeTe chalcogenide.

Intra-chain superexchange couplings in quasi-1D 3d transition-metal magnetic compounds

The electronic structure and magnetic properties of the quasi-1D transition-metal borates PbMBO4 (M  =  Ti, V, Cr, Mn, Fe, Co) have been investigated by density functional theory, including electronic correlation. The results evidence PbCrBO4 and PbFeBO4 as antiferromagnetic (AFM) semiconductors (intra-chain AFM and inter-chain FM) and PbMnBO4 as a ferromagnetic (FM) semiconductor (both intra- and inter-chain FM) in accordance with experimental observations. For non-synthesized PbTiBO4, PbVBO4, and PbCoBO4, the ground-state magnetic structures are paramagnetic, FM, and paramagnetic, respectively. In this series of compounds, there are two kinds of superexchange couplings dominating their magnetic properties, i.e. the direction M-M delocalization superexchange and indirect M-O-M correlation superexchange. For PbMBO4 with M (3+) d  (n) , n  ⩽  3 (M  =  V and Cr), the main intra-chain spin coupling is the M-M t 2g-t 2g direct delocalization superexchange, while for PbMBO4 with M (3+) d  (n) , n  >  3 (M  =  Mn and Fe), the main intra-chain spin coupling is the near 90° M-O-M e g-p-e g indirect correlation superexchange.

Synthesis, characterization, and mechanism analysis of S = 2 quasi-one-dimensional ferromagnetic semiconductor Pb2Mn(VO4)2(OH)

A brackebuschite-type compound Pb2Mn(VO4)2(OH) was synthesized by a hydrothermal method. Single crystal X-ray diffraction reveals that Pb2Mn(VO4)2(OH) crystallizes in the space group P21/m, with the structure built of single [010] chains of edge-shared MnO6 octahedra bridged by VO4-PbO6 groups along a and c axes, as a result forming a very large inter-chain distance of about 7.67 Å. The magnetic and optical measurements indicate that Pb2Mn(VO4)2(OH) is an S = 2 quasi-one-dimensional ferromagnetic semiconductor, with a very small specific value of intra- and inter-chain exchange coupling Jintra/Jinter = 10(-3), and a band gap of 1.72 eV. The electronic structure calculations indicate that a 90° Mn-O-Mn dpσ-dpσ correlation superexchange dominates the intra-chain ferromagnetic coupling in Pb2Mn(VO4)2(OH).

Ultrahigh resolution soft x-ray emission spectrometer at BL07LSU in SPring-8

An extremely high resolution flat field type slit less soft x-ray emission spectrometer has been designed and constructed for the long undulator beamline BL07LSU in SPring-8. By optimizing the ruling parameters of two cylindrical gratings, a high energy resolution ΔE < 100 meV and/or an E∕ΔE ~ 10 000 are expected for the energy range of 350 eV - 750 eV taking into account the broadening by the spatial resolution (25 μm) of a CCD detector. A coma-free operation mode proposed by Strocov et al., is also applied to eliminate both defocus and coma aberrations. The spectrometer demonstrated experimentally that E/ΔE = 10 050 and 8046 for N 1s (402.1 eV) and Mn 2p (641.8 eV) edges, respectively.