Magnetic dilution of a honeycomb lattice XY magnet CoTiO3

We report our study of cobalt (II) titanate, CoTiO3, in which magnetic Co ions are replaced by non-magnetic ions. The antiferromagnetic ordering transition of CoTiO3 around 37 K is described with ferromagnetic honeycomb layers coupled antiferromagnetically along the crystallographic c direction. The effect of magnetic dilution on the Néel temperature of this material is investigated through the doping of Zn2+ and Mg2+ in place of Co2+ for various dilution levels up to x + y = 0.46 in Co1-x-yZnxMgyTiO3. Single phase polycrystalline samples have been synthesized and their structural and magnetic properties have been examined. A linear relation between dilution and the Néel temperature is observed over a wide doping range. A linear extrapolation would suggest that the required dilution level to suppress magnetic order is around x + y ∽ 0.74, well beyond the classical percolation threshold. The implication of this observation for microscopic models for describing CoTiO3 is discussed.

Non-Fermi liquid behavior below the Néel temperature in the frustrated heavy fermion magnet UAu2

The term Fermi liquid is almost synonymous with the metallic state. The association is known to break down at quantum critical points (QCPs), but these require precise values of tuning parameters, such as pressure and applied magnetic field, to exactly suppress a continuous phase transition temperature to the absolute zero. Three-dimensional non-Fermi liquid states, apart from superconductivity, that are unshackled from a QCP are much rarer and are not currently well understood. Here, we report that the triangular lattice system uranium diauride (UAu2) forms such a state with a non-Fermi liquid low-temperature heat capacity C/T∼log (1/T) and electrical resistivity ρ(T)−ρ(0)∝T1.35 far below its Néel temperature. The magnetic order itself has a novel structure and is accompanied by weak charge modulation that is not simply due to magnetostriction. The charge modulation continues to grow in amplitude with decreasing temperature, suggesting that charge degrees of freedom play an important role in the non-Fermi liquid behavior. In contrast with QCPs, the heat capacity and resistivity we find are unusually resilient in magnetic field. Our results suggest that a combination of magnetic frustration and Kondo physics may result in the emergence of this novel state.

The Magnetic Susceptibility Bifurcation in the Ni-Doped Sb2Te3 Topological Insulator with Antiferromagnetic Order Accompanied by Weak Ferromagnetic Alignment

The magnetic susceptibility reveals a discontinuity at Néel temperature and a hysteresis loop with low coercive field was observed below Néel temperature. The magnetic susceptibility of zero field cool and field cool processes coincide at a temperature above the discontinuity, and they split at temperature blow the discontinuity. The magnetic susceptibility splitting is larger at lower external magnetic fields. No more magnetic susceptibility splitting was observed at a magnetic field above 7000 Oe which is consistent with the magnetic anisotropy energy. Our study supports that these magnetic susceptibility characteristics originate from an antiferromagnetic order accompanied by weak ferromagnetism.

Crystal structure and magnetic properties of the layered hybrid organic–inorganic compounds M 2(OH)2(C14H8O4) (M = Mn, Fe)

The structure of M 2(OH)2(bpdc) (bpdc = biphenyl dicarboxylate, C14H8O4) is distinct from that of the isoreticular compounds M 2(OH)2(bdc) (bdc = benzene dicarboxylate, C8H4O4) (M = Mn, Fe), in the sense that no disorder of the bpdc molecules from one layer to the other needs to be considered. The global symmetry is lower in the bpdc compounds (P 1) than in the bdc compounds (C2/m). Both Mn2(OH)2(bpdc) and Fe2(OH)2(bpdc) order magnetically at 36.8 and 46.5 K, respectively, and can be considered as uncompensated antiferromagnets, whereas Mn2(OH)2(bdc) (Néel temperature T N = 38.5 K) and Fe2(OH)2(bdc) (T N = 66 K) are compensated antiferromagnets.

The Effect of the In-Situ Heat Treatment on the Martensitic Transformation and Specific Properties of the Fe-Mn-Si-Cr Shape Memory Alloys Processed by HSHPT Severe Plastic Deformation

This work focuses on the temperature evolution of the martensitic phase ε (hexagonal close packed) induced by the severe plastic deformation via High Speed High Pressure Torsion method in Fe57Mn27Si11Cr5 (at %) alloy. The iron rich alloy crystalline structure, magnetic and transport properties were investigated on samples subjected to room temperature High Speed High Pressure Torsion incorporating 1.86 degree of deformation and also hot-compression. Thermo-resistivity as well as thermomagnetic measurements indicate an antiferromagnetic behavior with the Néel temperature (TN) around 244 K, directly related to the austenitic γ-phase. The sudden increase of the resistivity on cooling below the Néel temperature can be explained by an increased phonon-electron interaction. In-situ magnetic and electric transport measurements up to 900 K are equivalent to thermal treatments and lead to the appearance of the bcc-ferrite-like type phase, to the detriment of the ε(hcp) martensite and the γ (fcc) austenite phases.

Crystal growth and physical properties of an antiferromagnetic molecule: trans-dibromidotetrakis(acetonitrile)chromium(III) tribromide, [CrBr2(NCCH3)4](Br3)

The synthesis, crystal structure determination, magnetic properties and bonding interaction analysis of a novel 3d transition-metal complex, [CrBr2(NCCH3)4](Br3), are reported. Single-crystal X-ray diffraction results show that [CrBr2(NCCH3)4](Br3) crystallizes in space group C2/m (No. 12) with a symmetric tribromide anion and the powder X-ray diffraction results show the high purity of the material specimen. X-ray photoelectron studies with a combination of magnetic measurements demonstrate that Cr adopts the 3+ oxidation state. Based on the Curie–Weiss analysis of magnetic susceptibility data, the Néel temperature is found to be around 2.2 K and the effective moment (μeff) of Cr3+ in [CrBr2(NCCH3)4](Br3) is ∼3.8 µB, which agrees with the theoretical value for Cr3+. The direct current magnetic susceptibility of the molecule shows a broad maximum at ∼2.3 K, which is consistent with the theoretical Néel temperature. The maximum temperature, however, shows no clear frequency dependence. Combined with the observed upturn in heat capacity below 2.3 K and the corresponding field dependence, it is speculated that the low-temperature magnetic feature of a broad transition in [CrBr2(NCCH3)4](Br3) could originate from a crossover from high spin to low spin for the split d orbital level low-lying states rather than a short-range ordering solely; this is also supported by the molecular orbital diagram obtained from theoretical calculations.