Tan Yuen

Magnetic ordering in M(ox)(bpy) system (M=Fe, Co, Ni; ox=C2O42−; bpy=4,4′-bipyridine)

The temperature and field dependence of the magnetization have been measured to investigate the magnetic properties of the first oxalate–bpy mixed-ligand framework with a general formula M(ox)(bpy) (M = Fe(II), Co(II), Ni(II); ox = C2O42−; bpy = 4,4′-bipyridine). All compounds in the M(ox)(bpy) system crystallize in an orthorhombic structure with space group Immm (No. 71), in which the magnetic M ions form one-dimensional chains along the a axis. Spontaneous magnetic orderings with transition temperatures of 12, 13, and 26 K have been found for Fe(ox)(bpy), Co(ox)(bpy), and Ni(ox)(bpy), respectively. The nature of the ordering in Ni(ox)(bpy) is antiferromagnetic, however it may exhibit a metamagnetic transition at high magnetic fields. The type of ordering in Fe(ox)(bpy) and Co(ox)(bpy) is also antiferromagnetic but with canting, or so-called weak ferromagnetism. The residual moment resulting from the canting is larger in Fe(ox)(bpy) than in Co(ox)(bpy). The values of μeff obtained by fitting χ(T) indicat...

A three-dimensional honeycomb-like network constructed with novel one-dimensional S-shaped chains via hydrogen bonding and π–π interactions

The solid compound formulated as [Cu(4,7-phen)-(H2O)3](ClO4)2·(4,7-phen)2 (phen=phenanthroline) has been shown by single-crystal structural analysis to be a three-dimensional network with hexagonal channels, constructed of one-dimensional S-shaped [Cu(4,7-phen)(H2O)3]n2n+ cationic chains and solvated 4,7-phen molecules, linked through extensive hydrogen bonds and π–π interactions.

Thermodynamic and magnetic properties of the tetravalent rare‐earth perovskite system BaPrO3

The temperature dependence of the magnetic susceptibility χ(T) and heat capacity C(T), the temperature and field dependence of the magnetization M(T,H), and neutron diffraction have been measured in the tetravalent perovskite system BaPrO3. A clear anomaly, observed in C(T), χ(T), and neutron scattering data at 11.7 K is attributed to antiferromagnetic alignment of Pr. Magnetization indicates that this ordering is insensitive to magnetic fields with TN being independent of H for H<12 T. High‐field isotherms show an upward kink in slope at 12.7 T independent of temperature for T<9.5 K, suggestive of a spin reorientation transition. 119Sn Mossbauer data for BaPr0.95Sn0.05O3 indicate a quadrupole splitting at 300 K that broadens below TN due to a hyperfine field.

Anomalous thermodynamic, transport and Mössbauer properties of UNiSn: A half-metallic system

Abstract Of the ternary actinide compounds UTX where T is a transition metal and X is a group III, IV or V element, UNiSn is one of the more interesting, displaying anomalous behavior in the resistivity in the form of a pronounced maximum. In this paper, we present precision measurements of the electrical resistivity, low-field magnetization and specific heat which indicate that the system is paramagnetic at high temperatures and undergoes a second-order transition to a magnetically ordered state at 43 K. 119Sn Mossbauer spectroscopy shows that the hyperfine field seen at the Sn sites does not decrease to zero as T = 43 K is approached from below but continues to be detectable to temperatures approaching 55 K suggesting that the magnetic correlations persist well above the transition temperature. However, the percentage of Sn nuclei that see the hyperfine field decreases dramatically at 43 K. This data is consistent with recent neutron-scattering data that indicate that the system orders antiferromagnetically.

Magnetic properties of some tetravalent rare-earth perovskites

The temperature dependence of the magnetic susceptibility for 1.5<T<300 K, the field dependence of the magnetization M(H), for 0<H<23 T and 1.5<T<15 K, and the temperature dependence of the heat capacity C(T), for 5<T<95 K are reported for the insulating distorted‐perovskite systems PrBaO3, TbBaO3, TbSrO3, and CeBaO3, and the pseudoternary system (Pr,Ce)BaO3. X‐ray analysis at room temperature indicates single‐phase structures for all materials. PrBaO3 shows magnetic ordering below TN=11.7 K, possibly due to a canted antiferromagnetic structure. TN is nearly independent of applied field up to about 12 T. High‐field M(H) isotherms show a well‐defined upward sloping kink at 12.7 T, which is independent of temperature for T<9.5 K. This is indicative of a spin‐reorientation transition. The pressure dependence of TN is negligible: dTN/dP<0.1 K/kbar. TbBaO3 and TbSrO3 both show antiferromagnetic ordering, but with low‐ field hysteresis effects below 34 K. Clear C(T) anomalies at TN=11.7 and 34 K are seen for Pr...

Thermal and magnetic properties of CeGe2

The magnetization data measured at low applied fields show that CeGe2 undergoes an antiferromagnetic transition at TN=7 K and exhibits a second ferromagnetic transition at TC=4.3 K. As the applied field increases, TC increases, but TN is almost unchanged. These two magnetic transitions merge to become a single ferromagnetic transition at a field equal to or larger than 5 kG. This is the first report of an antiferromagnetic transition in CeGe2 and the data are significantly different from those previously reported. The high temperature magnetic susceptibility shows the Curie–Weiss behavior and the effective paramagnetic moment is 2.38 μB indicating that the Ce ions in CeGe2 are trivalent. The specific heat data also show anomalies at 4.3 and 7 K associated with two magnetic transitions, respectively. An enhanced electronic specific heat coefficient of γHT=120 mJ/mol K2 is deduced for temperatures above TN.

119Sn Mössbauer study of magnetic structure in Sn-doped UPb3 and UIn3

Abstract The temperature dependences of Mossbauer spectra, magnetic susceptibility and specific heat have been measured for U(In 1− x Sn x ) 3 and U(Pb 1− x Sn x ) 3 . The low temperature 119 Sn Mossbauer spectra of U(Pb 1− x ) 3 for 0.02 ≤ x ≤ 0.85 and U(In 1− x Sn x ) 3 for 0.02 ≤ x ≤ 0.6 show the existence of a magnetic hyperfine field at the Sn sites. The results for both systems indicate that the magnetic structures of the Pb-rich and In-rich pseudobinary alloys is incompatible with the magnetic structures previously proposed on the basis of neutron diffraction data for pure UPb 3 and Ulp 3 . An identical magnetic structure is proposed for both systems, having a magnetic unit cell of (2 a , 2 a , 2 a ) (where a is the lattice constant of the crystal unit cell) and in which the U magnetic moments alternate between the eight possible [±1, ±1, ±1] directions. The new structure is consistent with both neutron diffraction and Mossbauer results.

Synthesis, structure, and magnetic properties of M(N3)2(bpy)

Powder crystalline metal-organic frameworks (MOF), M(N3)2(bpy) (where M = Ni, Co, Cu, and bpy = 4,4′-bipyridine), were successfully synthesized by mixing M(II) salts with solutions of 4,4′-bipyridine and NaN3. All three MOFs crystallize in an orthorhombic crystal system with the space group Cmmm (No. 65), which is isostructural to that of 2D-Fe(N3)2(bpy). The M(II) ions are coordinated with four azide ligands (N3) in equatorial plane forming linear magnetic chains. Isothermal magnetization, magnetic susceptibility, and heat capacity measurements were performed. No clear phase transitions were observed. The intra-chain magnetic interaction was found to be ferromagnetic for the Co and Ni compounds, and antiferromagnetic for the Cu compound. The data were fit to theoretical models, and the variation in the exchange interactions was interpreted in terms of the geometric distortions on the octahedral M(II) sites.

Study of magnetic ordering states of CeGex with 1.66<x⩽2.0

The existence of an antiferromagnetic transition at TN=7 K is reported for CeGex with a small range of Ge concentration of 1.66<x<1.71. Measurements of x-ray diffraction and the temperature and magnetic field dependence of magnetization and specific heat have been carried out for CeGex with 1.66⩽x⩽2.0. The magnetic ground state and the crystal structure change abruptly near a Ge concentration of x=1.710. Within the range of Ge concentrations between x=1.71 and 2.0, CeGex crystallizes in the orthorhombic structure and exhibits two magnetic transitions: an antiferromagnetic transition at TN=7 K and a ferromagnetic transition at TC=4.3 K. Interestingly, when x is lowered to 1.66<x<1.71, CeGex crystallizes in a tetragonal phase, exhibits an antiferromagnetic transition at TN=7 K, and remains in the antiferromagnetic state down to a temperature of 0.5 K.

Studies of thermodynamic and magnetic properties of Ce1−xGdxSn3

The temperature dependence of the specific heat, magnetic susceptibility, and 119Sn Mossbauer spectra of Ce1−xGdxSn3 has been measured. An evolution from mixed valent, to enhanced paramagnetic, to spin glass, and finally to a magnetically ordered state is observed as one alloys from pure CeSn3 to GdSn3. The C/T curves show a strong upswing at the lowest temperatures for the enhanced paramagnetic systems with dilute Gd concentrations. In the spin‐glass regime, the temperature where the cusp occurs in the zero‐field cooled magnetic susceptibility data is lower than the temperature at which the Mossbauer line width starts broadening. For the magnetically ordered state, TN increases with increasing Gd concentration reaching 31 K for pure GdSn3.