Electrical Resistivity, Magnetic Susceptibility, X-Ray Photoelectron Spectroscopy, and Electronic Band Structure Studies of Cu2.33−xV4O11

The electronic and physical properties of Cu_2.33V₄O₁₁ were characterized by electrical resistivity, magnetic susceptibility and X-ray photoelectron spectroscopy (XPS) measurements and by tight-binding electronic band structure calculations. Attempts to prepare Cu_2.33−xV₄O₁₁ outside its narrow homogeneity range led to a mixture of Cu_2.33V₄O₁₁, CuVO₃ and β-Cu_xV₂O₅. The magnetic susceptibility data show no evidence for a magnetic/structural transition around 300 K. The XPS spectra of Cu_2.33V₄O₁₁ reveal the presence of mixed valence in both Cu and V. The [Cu⁺]/[Cu²⁺] ratio is estimated to be 1.11 from the Cu 2p_3/2 peak areas, so [V⁴⁺]/[V⁵⁺]=0.56 by the charge balance. Our electronic structure calculations suggest that the oxidation state of the Cu ions is +2 in the channels of CuO₄ tetrahedra, and +1 in the channels of linear CuO₂ and trigonal planar CuO₃ units. This predicts that [Cu⁺]/[Cu²⁺]=1.33 and [V⁴⁺]/[V⁵⁺]=0.50, in good agreement with those deduced from the XPS study.     

Synthesis and characterization of a magnetic semiconductor Na(2)RuO(4) containing one-dimensional chains of Ru(6+)

A new ternary ruthenium oxide Na(2)RuO(4) was prepared and shown to crystallize with a new structure type. Single crystal X-ray diffraction measurements reveal that Na(2)RuO(4) consists of RuO(4) chains made up of RuO(5) trigonal bipyramids by sharing axial corners. Na(2)RuO(4) is a magnetic semiconductor with a variable range hopping behavior, and its molar magnetic susceptibility chi(mol) has a broad maximum at approximately 74 K. The derivative d(chi(mol).T)/dT exhibits a peak at 37.7 K which has been confirmed by heat capacity measurement to be due to long-range antiferromagnetic ordering.     

Structure and magnetic properties of oxychalcogenides A2F2Fe2OQ2 (A = Sr, Ba; Q = S, Se) with Fe2O square planar layers representing an antiferromagnetic checkerboard spin lattice

The oxychalcogenides A2F2Fe2OQ2 (A = Sr, Ba; Q = S, Se), which contain Fe2O square planar layers of the anti-CuO2 type, were predicted using a modular assembly of layered secondary building units and subsequently synthesized. The physical properties of these compounds were characterized using magnetic susceptibility, electrical resistivity, specific heat, (57)Fe Mossbauer, and powder neutron diffraction measurements and also by estimating their exchange interactions on the basis of first-principles density functional theory electronic structure calculations. These compounds are magnetic semiconductors that undergo a long-range antiferromagnetic ordering below 83.6-106.2 K, and their magnetic properties are well-described by a two-dimensional Ising model. The dominant antiferromagnetic spin exchange interaction between S = 2 Fe(2+) ions occurs through corner-sharing Fe-O-Fe bridges. Moreover, the calculated spin exchange interactions show that the A2F2Fe2OQ2 (A = Sr, Ba; Q = S, Se) compounds represent a rare example of a frustrated antiferromagnetic checkerboard lattice.     

On the magnetic insulating states, spin frustration, and dominant spin exchange of the ordered double-perovskites Sr2CuOsO6 and Sr2NiOsO6: density functional analysis

The ordered double-perovskites Sr(2)MOsO(6) (M = Cu, Ni) consisting of 3d and 5d transition-metal magnetic ions (M(2+) and Os(6+), respectively) are magnetic insulators; the magnetic susceptibilities of Sr(2)CuOsO(6) and Sr(2)NiOsO(6) obey the Curie-Weiss law with dominant antiferromagnetic and ferromagnetic interactions, respectively, and the zero-field-cooled and field-cooled susceptibility curves of both compounds diverge below ～20 K. In contrast, the available density functional studies predicted both Sr(2)CuOsO(6) and Sr(2)NiOsO(6) to be metals. We resolved this discrepancy on the basis of systematic density functional calculations. The magnetic insulating states of Sr(2)MOsO(6) are found only when a substantially large on-site repulsion is employed for the Os atom, although it is a 5d element. The cause for the divergence between the zero-field-cooled and field-cooled susceptibility curves in both compounds and the reason for the difference in their dominant magnetic interactions were investigated by examining their spin exchange interactions.     

Analogies between Jahn–Teller and Rashba spin physics

In developing physical theories, analogical reasoning has been found to be very powerful, as attested by a number of important historical examples. An analogy between two apparently different phenomena, once established, allows one to transfer information and bring new concepts from one phenomenon to the other. Here, we discuss an important analogy between two widely different physical problems, namely, the Jahn–Teller distortion in molecular physics and the Rashba spin splitting in condensed matter physics. By exploring their conceptual and mathematical features and by searching for the counterparts between them, we examine the orbital texture in Jahn–Teller systems, as the counterpart of the spin texture of the Rashba physics, and put forward a possible way of experimentally detecting the orbital texture. Finally, we discuss the analogy by comparing the coexistence of linear Rashba + Dresselhaus effects and Jahn–Teller problems for specific symmetries, which allow for nontrivial spin and orbital textures, respectively.     

Synthesis, crystal structure, magnetic properties, and electronic structure of the new ternary vanadate CuMnVO4

A new magnetic oxide, CuMnVO4, was prepared, and its crystal structure was determined by single-crystal X-ray diffraction. The magnetic properties of CuMnVO4 were characterized by magnetic susceptibility and specific heat measurements, and the spin exchange interactions of CuMnVO4 were analyzed on the basis of spin-polarized electronic band structure calculations. CuMnVO4 contains MnO4 chains made up of edge-sharing MnO6 octahedra containing high-spin Mn2+ cations. Our work shows that CuMnVO4 undergoes a three-dimensional antiferromagnetic transition at approximately 20 K. Both the intrachain and interchain spin exchanges are antiferromagnetic, and the interchain spin exchange is not negligible compared to the intrachain spin exchange.     

Investigation of the crystal structure and the structural and magnetic properties of SrCu2(PO4)2

SrCu2(PO4)2 was prepared by the solid-state method at 1153 K. Its structure was solved by direct methods in the space group Pccn (No. 56) with Z = 8 from synchrotron X-ray powder diffraction data measured at room temperature. Structure parameters were then refined by the Rietveld method to obtain the lattice parameters, a = 7.94217(8) A, b = 15.36918(14) A, and c = 10.37036(10) A. SrCu2(PO4)2 presents a new structure type and is built up from Sr2O16 and Cu1Cu2O8 units with Cu1...Cu2 = 3.256 A. The magnetic properties of SrCu2(PO4)2 were investigated by magnetic susceptibility, magnetization up to 65 T, Cu nuclear quadrupole resonance (NQR), electron-spin resonance, and specific heat measurements. With spin-dimer analysis, it was shown that the two strongest spin-exchange interactions between Cu sites result from the Cu1-O...O-Cu2 and Cu2-O...O-Cu2 super-superexchange paths with Cu1...Cu2 = 5.861 A and Cu2...Cu2 = 5.251 A, and the superexchange associated with the structural dimer Cu1Cu2O8 is negligible. The magnetic susceptibility data were analyzed in terms of a linear four-spin cluster model, Cu1-Cu2-Cu2-Cu1 with -2J(1)/kB = 82.4 K for Cu1-Cu2 and -2J(2)/k(B) = 59 K for Cu2-Cu2. A spin gap deduced from this model (Delta/kB = 63 K) is in agreement with that obtained from the Cu NQR data (Delta/kB = 65 K). A one-half magnetization plateau was observed between approximately 50 and 63 T at 1.3 K. Specific heat data show that SrCu2(PO4)2 does not undergo a long-range magnetic ordering down to 0.45 K. SrCu2(PO4)2 melts incongruently at 1189 K. We also report its vibrational properties studied with Raman spectroscopy.     

Comparative electronic band structure study of the intrachain ferromagnetic versus antiferromagnetic coupling in the magnetic oxides Ca3Co2O6 and Ca3FeRhO6

In the (MM'O6)infinity chains of the transition-metal magnetic oxides Ca3MM'O6 the MO6 trigonal prisms alternate with the M'O6 octahedra by sharing their triangular faces. In the (Co(2O6)infinity chains of Ca3Co2O6 (M = M' = Co) the spins are coupled ferromagnetically, but in the (FeRhO6)infinity chains of Ca3FeRhO6 (M = Fe, M' = Rh) they are coupled antiferromagnetically. The origin of this difference was probed by carrying out spin-polarized density functional theory electronic band structure calculations for ordered spin states of Ca3Co2O6 and Ca3FeRhO6. The spin state of a (MM'O6)infinity chain determines the occurrence of direct metal-metal bonding between the adjacent trigonal prism and octahedral site transition-metal atoms. The extent of direct metal-metal bonding in the (Co2O6)infinity chains of Ca3Co2O6 is stronger in the intrachain ferromagnetic state than in the intrachain antiferromagnetic state, so that the intrachain ferromagnetic state becomes more stable than the intrachain antiferromagnetic state. Such a metal-metal-bonding-induced ferromagnetism is expected to occur in magnetic insulators and magnetic metals of transition-metal elements in which direct metal-metal bonding can be enhanced by ferromagnetic ordering. In the (FeRhO6)infinity chains of Ca3FeRhO6 the ferromagnetic coupling does not lead to a strong metal-metal bonding and the adjacent spins interact by the Fe-O...O-Fe super-superexchange, hence leading to an antiferromagnetic coupling.