Magnetic susceptibilities of UO2ThO2 solid solutions

The magnetic susceptibility of UO₂ThO₂ solid solutions has been measured from room temperature to 2.0 K. The magnetic moment and the Weiss constant have been determined in the temperature range in which the Curie-Weiss law holds. For the solid solutions showing antiferromagnetic transition, the Néel temperature has been also determined. These values decrease monotonically with increasing ThO₂ concentration. The results were analyzed using the molecular field theory which includes the interaction between next-nearest neighbor spins. The interactions between nearest neighbor spins, J₁, and those between next-nearest neighbor spins, J₂, both decrease with increasing ThO₂ concentration. The change of J₁ with composition is larger than that of J₂. The effect of magnetic dilution with ThO₂ is considered to be stronger on the interaction between nearest neighbor uranium ions.     

Magnetic and Crystallographic Properties of LnCrO4 (Ln=Nd, Sm, and Dy)

Zircon-type compounds LnCrO₄ (Ln=Nd, Sm, and Dy) were prepared. Their precise crystal structures at room temperature were determined from X-ray diffraction measurements. These compounds have a tetragonal system with space group I4₁/amd. Magnetic susceptibility and specific heat measurements have been performed for all the compounds in the temperature range between 1.8 and 300 K. For NdCrO₄, an antiferromagnetic transition was found at 25.2 K. SmCrO₄ and DyCrO₄ show magnetic transitions at 15.0 and 22.8 K, respectively. In addition, structural phase transitions were observed at 58.5 and 31.2 K, respectively. For DyCrO₄, the crystal structure below the transition temperature was determined by low-temperature powder X-ray diffraction measurements to be orthorhombic with space group Imma.     

Synthesis and magnetic properties of ALnO2 (A=Cu or Ag; Ln=rare earths) with the delafossite structure

Synthesis, structures, and magnetic properties of ternary rare earth oxides ALnO₂ (A=Cu or Ag; Ln=rare earths) have been investigated. CuLnO₂ (Ln=La, Pr, Nd, Sm, Eu) were synthesized by the direct solid state reaction of Cu₂O and Ln₂O₃, and AgLnO₂ (Ln=Tm, Yb, Lu) were obtained by the cation-exchange reaction of NaLnO₂ and AgNO₃ in a KNO₃ flux. These compounds crystallized in the delafossite-type structure with the rhombohedral 3R type (space group: R-3m). Magnetic susceptibility measurements showed that these compounds are paramagnetic down to 1.8 K. Specific heat measurements down to 0.4 K indicated that CuNdO₂ ordered antiferromagnetically at 0.8 K.     

Reversible mechanochromic luminescence of [(C6F5Au)2(mu-1,4-diisocyanobenzene)

Reversible mechanochromic luminescence of [(C6F5Au)2(mu-1,4-diisocyanobenzene)] is reported. Grinding of the complex induced a photoluminescent color change, which was restored by exposure to a solvent. This cycle was repeated 20 times with no color degradation in the emissions. Their optical properties, X-ray crystallographic analysis, IR, and XRD measurements strongly suggested that the change in the molecular arrangement is responsible for this mechanochromic property. Intermolecular aurophilic bondings presumably play a key role in the altered emission.     

Orthogonal spin arrangement in quasi-two-dimensional La2Co2O3Se2

The crystal, electronic, and magnetic structures of the cobalt oxyselenide La(2)Co(2)O(3)Se(2) were investigated through powder neutron diffraction measurements and band structure calculations. This oxyselenide crystallizes in a tetragonal layered structure with space group I4/mmm. The Co ion is sixfold-coordinated by two oxide ions and four selenide ions, and the face-sharing CoO(2)Se(4) octahedra form Co(2)OSe(2) layers. The band structure calculations revealed that the Co ion is in the divalent high-spin state. Rietveld analysis of the neutron diffraction profiles below 200 K demonstrated that the Co moments have a noncollinear antiferromagnetic structure with the propagation vector k = (?, ?, 0). The ordered magnetic moment was determined to be 3.5 μ(B) at 10 K, and the directions of the nearest-neighbor Co moments are orthogonal each other in the c plane.     

Magnetic and calorimetric studies on rare-earth iron borates LnFe3(BO3)4 (Ln=Y, La-Nd, Sm-Ho)

A series of rare-earth iron borates having general formula LnFe₃(BO₃)₄ (Ln=Y, La-Nd, Sm-Ho) were prepared and their magnetic properties have been investigated by the magnetic susceptibility, specific heat, and ⁵⁷Fe Mössbauer spectrum measurements. These borates show antiferromagnetic transitions at low temperatures and their magnetic transition temperatures increase with decreasing Ln³⁺ ionic radius from 22 K for LaFe₃(BO₃)₄ to 40 K for TbFe₃(BO₃)₄. In addition, X-ray diffraction, specific heat, and differential thermal analysis (DTA) measurements indicate that the phase transition occurs for the LnFe₃(BO₃)₄ compounds with Ln=Eu-Ho, Y, and its transition temperature increases remarkably with decreasing Ln³⁺ ionic radius from 88 K for Ln=Eu to 445 K for Ln=Y.     

Magnetic and neutron diffraction study on melilite-type oxides Sr2MGe2O7 (M = Mn, Co)

The crystal structures and magnetic properties of melilite-type oxides Sr(2)MGe(2)O(7) (M = Mn, Co) were investigated. These compounds crystallize in the melilite structure with space group P ?42(1)m, in which the M and Ge ions occupy two kinds of tetrahedral sites in an ordered manner. The magnetic M ions form a square-planar lattice in the ab plane. Both compounds do not show the structural phase transition down to 2.5 K. The temperature dependence of magnetic susceptibility for Sr(2)MnGe(2)O(7) shows a broad peak at ~6.0 K because of a two-dimensional magnetic interaction between Mn ions in the ab plane. At 4.4 K, an antiferromagnetic transition was observed. The magnetic structure was determined by the neutron powder diffraction measurements at 2.5 K. It can be represented by the propagation vector k = (0, 0, 1/2), and the magnetic moments of Mn(2+) (3.99 μ(B)) ions order antiferromagnetically in a collinear manner along the c axis. On the other hand, Sr(2)CoGe(2)O(7) shows an antiferromagnetic transition at 6.5 K with divergence between zero-field-cooled and field-cooled susceptibilities. Its magnetic structure determined at 2.5 K has a magnetic propagation vector k = (0, 0, 0), and the ordered magnetic moment of Co(2+) (2.81 μ(B)) adopts a collinear arrangement lying on the ab plane.     

Studies on magnetic and calorimetric properties of double perovskites Ba2HoRuO6 and Ba2HoIrO6

Magnetic properties of double perovskite compounds Ba₂HoRuO₆ and Ba₂HoIrO₆ have been reported. Powder X-ray and neutron diffraction measurements show that these compounds have a cubic perovskite-type structure with the space group and the 1:1 ordered arrangement of Ho³⁺ and Ru⁵⁺ (or Ir⁵⁺) over the 6-coordinate B sites. Results of the magnetic susceptibility and specific heat measurements show that Ba₂HoRuO₆ exhibits two magnetic anomalies at 22 and 50 K. Analysis of the temperature dependence of magnetic specific heat indicates that the anomaly at 50 K is due to the antiferromagnetic ordering of Ru⁵⁺ ions and that the anomaly at 22 K is ascribable to the magnetic interaction between Ho³⁺ ions. Neutron diffraction data collected at 10 and 35 K show that the Ba₂HoRuO₆ has a long range antiferromagnetic ordering involving both Ho³⁺ and Ru⁵⁺ ions. Each of their magnetic moments orders in a Type I arrangement and these magnetic moments are anti-parallel in the ab-plane with each other. The magnetic moments are aligned along the c-direction. On the other hand, Ba₂HoIrO₆ is paramagnetic down to 1.8 K.