Field Dependence Of Magnetic Susceptibility Research Articles

Cobalt (II)-hydroxide terephthalate - a metamagnet with a large coercive field

We present the field dependent magnetization and magnetic susceptibility of an unusual metamagnet Co 2 (OH) 2 (O 2 CC 6 H 4 CO 2 ). It is characterized by a maximum in the susceptibility at the Neel temperature of 48 K and by spontaneous magnetization at a T C of 43 K due to a small canting. It displays the characteristic kink of a metamagnetic transition in the field-dependent magnetization below T N . Below T C hysteresis is observed whose width increases to span ± 5.2 T at 1.5 K. We propose a qualitative explanation of the rich phase behaviour.

SQUID microsusceptometry in applied magnetic fields

We describe the design and construction of a planar dc SQUID susceptometer to characterize microcrystallites as a function of temperature from 0.3 K to 4 K in magnetic fields exceeding 280 G. Eliminating the need for magnetic shielding permits broader application of SQUIDs to characterization of small spin ensembles. We present temperature- and field-dependent magnetic susceptibility data on crystallites mounted directly on the surface of a SQUID chip. Large, in-plane static fields are applied through an external coil while perpendicular fields up to 2 G can be applied by a series-wound on-chip field coil. Paramagnetic, antiferromagnetic, and superconducting transitions have been resolved on samples of order 20 to 50 /spl mu/m (30 to 500 picomoles, /spl sim/5/spl times/10/sup 16/ emu/Hz/sup 1/2/.) We discuss the effects of sample shape and location on the spin calibration of the assembled susceptometer.

Synthesis, Crystal Structure, and Magnetic Properties of La4Co3O10+δ(0.00≤δ≤0.30)

The effects of nonstoichiometry on the crystal structure, thermal expansion, structural phase transitions, and magnetic properties of La4Co3O10+δ, 0.00≤δ≤0.30, have been investigated between 2 and 1000 K. Rietveld analysis of high resolution powder X-ray diffraction data reveals the crystal structure of La4Co3O10+δ(Ruddlesden–Popper type phase; Lan+1ConO3n+1withn=3) to be slightly monoclinically distorted, space groupC2/m. The monoclinic distortion increases and the unit cell volume decreases slightly on increasing nonstoichiometry,δ. A structural phase transition, monoclinic to tetragonal, possibly via an intermediate orthorhombic state, occurs at 840 K. Magnetic susceptibility data indicate long-range antiferromagnetic ordering belowTN≈13 K. Above 20 K there are three temperature regimes with nearly Curie–Weiss paramagnetic behaviour for the magnetic susceptibility: 20–80 K, 100–450 K, 650–985 K. This indicates a temperature-induced change from a lower, possibly via an intermediate, to a higher spin configuration for CoIIIcomparable to that described for LaCoO3. Field-dependent magnetic susceptibility is observed forδ>0.00 forT<100 K.

Thermodynamical study under hydrostatic pressure of MnSi

We report a study under pressure on the field dependence of magnetic susceptibility χ( H) and magnetoresistivity ϱ( H) on single crystals of the weakly itinerant helimagnet system MnSi. Close to the critical pressure P c = 14.8 kbar, the shapes of χ( H) and ϱ( H) indicate some metamagnetic behaviors induced by the external magnetic field.

Metamagnetic behavior induced by hydrostatic pressure in MnSi

We report a study under pressure on the field dependence of magnetic susceptibility χ( H) and magnetoresistivity ϱ( H) on single crystals of the weakly itinerant helimagnet system MnSi. Close to the critical pressure P c = 14.8 kbar, the shapes of χ( H) and ϱ( H) indicate some metamagnetic behaviors induced by the external magnetic field.

Magnetic properties of the two-dimensional ‘‘triangles-in-triangles’’ Kagomé lattice Cu9X2(cpa)6 (X=F,Cl,Br)

Magnetic properties of the isostructural series of compounds known as Cu9X2(cpa)6 (cpa=carboxypentonic acid; X=F,Cl,Br) are reported as a function of the μ3-halide ion. The interconnection topology within each layer is a hexagonal arrangement of trimeric units, i.e., a ‘‘triangles-in-triangles’’ Kagomé lattice. Magnetic field dependent susceptibility data in the range 1.7–250 K demonstrate that all three compounds have a magnetic ground state which is highly field dependent at lower temperatures, but that phase transitions to long-range order are not observed down to 1.7 K. Development of 2-D antiferromagnetic models appropriate for the chemical nature and symmetry of the Cu9X2(cpa)6 lattice will require a two J-value solution (intratrimer and intertrimer), and although theoretical results for this type of lattice are as yet unknown, analogies can be clearly drawn to the Kagomé problem. The Curie–Weiss temperatures in the range of −250 K strongly suggest spin frustration in the absence of any traditional long-range order. Magnetization studies exhibit an intermediate saturation level corresponding to a ground state of one unpaired spin per unit cell at field values well below 1.0 kG, supporting the conclusion that the two J values are antiferromagnetic.

Crystallographic and Magnetic Studies of Nb 0.97Fe 0.947M 0.106O 3.79F 0.21 ( M = Ni, Co)

The crystallographic structures of the oxyfluoride phases Nb 0.947Fe 0.947M 0.106O 3.79F 0.21 ( M = Ni, Co) are refined from their X-ray powder diffraction pattern by means of a Rietveld method in the wolframite structural type. Both compounds exhibit a partial cationic disorder, i.e., between Nb V on one hand and the magnetic cations (Fe III and Ni II or Co II) on the other hand. The cobalt-containing phase is more ordered than the nickel-containing phase. The consequence of incomplete order is a field-dependent magnetic susceptibility at low temperatures. Alternative susceptibility measurements versus temperature exhibit a maximum around 35 K.

Relation between Structural and Magnetic Properties of Nb0.94Fe1.06O3.76F0.24

The oxyfluoride phases xNbFeO4-(1 - x )FeF2 have been synthesized. They exist in a limited range 0.8 < x < 1. They are isomorphous with NbFeO4, having the wolframite structure. The refinement of the crystallographic structure of the oxyfluoride phase Nb0.94Fe1.06O3.76F0.24 using a Rietveld method has pointed out a partial cationic disorder between niobium and iron. The consequence of incomplete order is a field-dependent magnetic susceptibility at low temperatures. Ac susceptibility measurements versus temperature exhibit a maximum at 35 K. Mössbauer measurements show that the valence is localized.

Low-Temperature X-ray Structure Determinations, and Single Crystal Magnetic Susceptibility and EPR Studies on (3-Chloroanilinium)8[CuCl6]Cl4

Abstract A recent X-ray diffraction study has shown that (3-chloro-anilinium)8[CuCl6]Cl4 contains compressed [CuCl6]4_ octahedra. Low tempera ture studies reported here do not obviate such a conclusion, and so, questions concerning disorder and dynamics still remain. Down to 110 K, the [CuCl6]4_ions are arranged in a quasi-linear chain. SQUID-based temperature-dependent magnetic susceptibility data exhibit maaximum near 17 K. The Bonner-Fisher model yields an antiferromagnetic Heisenberg exchange of J = -9.3 cm−1. Magnetic field-dependent susceptibility measurements on single crystals with the chain-axis aligned parallel to the field, show a marked field dependence below 9 K and suggest weak ferromagnetism due to spin canting. Single crystal EPR measurements at room temperature yield g∥ = 2.035 and a single g⊥= 2.202; at 4 K, g∥ = 2.041 with g⊥1 = 2.200 and g⊥2 = 2.168. Line widths in all orientations at 4 K are very narrow, ranging from 0.5 to 2.0 mT.

Magnetic and electrical properties of the tetragonal U(Cu, Ni) 2− xGa 2+ x phases

A new family of U(Cu, Ni) 2− x Ga 2+ x compounds crystallizing in the I4/mmm space group has been identified by means of powder X-ray diffraction analysis. The tetragonal U-Cu-Ga ternaries exist in a wide homogeneity range for 0.166 ⩽ x ⩽ 0.5 as well as the copper-deficient UCu 2(1− x)Ga 2+ x phases. A tetragonal nickel derivative occurs only for x = 1 as UNiGa 3 with the BaNiSn 3-type symmetry ( I4 mm) or it may adopt a new type of crystal structure with the I4 m2 space group. All the copper ternaries were found to be antiferromagnets with a Néel temperature of around 50 K. The field dependence of magnetic susceptibility at 4.2 K indicates a non-collinear magnetic structure. The X( T) function of UNiGa 3 shows a sharp maximum at 34 K and exhibits no magnetic field dependence at liquid-helium temperature. For all the ternaries examined, the electrical resistivity increases slightly with decrease in temperature and falls below the Néel temperature. The most abrupt change is observed for UNiGa 3.

On the Meissner effect in granular superconductors

The magnetic field dependence of Meissner susceptibility of ceramics samples with different grain size was studied. It was found that the behaviour of susceptibility in sintered samples can be nonmonotonous. The model based on magnetic flux freezing when crossing the “irreversibility line” is proposed. The equation of the “irreversibility line” for the Josephson vortex system is obtained. In the framework of the model the experimental magnetic field dependence of susceptibility and the role of ceramics grain size are described in a qualitative manner.

Magnetic Susceptibility of U1-xGdxO2Solid Solution

Magnetic susceptibility was measured on the samples of U1--xGdxO2 prepared by a co-precipitation method from 1.7 K to room temperature. The behavior of magnetic susceptibility is contributed almost from trivalent gadolinium ion because of its very large spin magnetic moment of 8S. For x≲540%, the magnetic susceptibility-temperature curve obeyed Curie-Weiss law and values of magnetic susceptibility increase linearly with increasing gadolinium concentrations. For the higher concentrations of gadolinium the magnetic susceptibility-temperature curve has a peak at 3–4 K, showing a magnetic field dependence of magnetic susceptibility at liquid helium temperature which would be expected for the case of a weak magnetic anisotropy in antiferromagnets.

Investigation of the magnetic properties of β-boron doped with carbon

The results of an investigation of the magnetic properties of carbondoped boron crystals (carbon content, 0.5–3.5 at.%) in the temperature range 77–300 K are presented. The temperature and field dependence of magnetic susceptibility were investigated using electron paramagnetic resonance (EPR) and magnetoresistance methods. It was found that carbon atoms are donors substituting boron atoms in the lattice. The EPR signal g = 4.28 is due to Fe 3+ ions in a glass-type phase. The magnetoresistance of carbon-doped samples decreases at 0.6–0.8 T and the mechanism seems to be the same as for negative magnetoresistance.

STUDIES OF ELECTRON STRUCTURE AND MAGNETISM OF WC

UV-Photoelectron spectroscopy (UPS) and X-ray photoelectron speetroseopy (XPS) were used to study the electronic structure of WC, Pt and W, and high sensitive magnetometer was employed to measure the temperature dependence and field dependence of magnetic susceptibility of WC and W in the temperature range 1.5-300K. The susceptibility of W did not change with temperature, it exhibits the behaviour of Pau-liparamagnetism. But WC was entirely different, for which the Curie's law was valid. Because unpaired spins exist in WC, we made the following hypothesis: Due to the influence of carbon in WC, 5d electrons of W were no longer be itinerent thoroughly. Like Pt, part of their valence electrons became localized. The appearenee of localized electron in WC is the cause of behaving platinum-like catalystic activity.

Magnetic susceptibility of U1-xGdxO2 solid solution.

Magnetic susceptibility was measured on the samples of U1-xGdxO2 prepared by a coprecipitation method from 1.7 K to room temperature. The behavior of magnetic susceptibility is contributed almost from trivalent gadolinium ion because of its very large spin magnetic moment of 8S. For x<40%, the magnetic susceptibility-temperature curve obeyed Curie-Weiss law and values of magnetic susceptibility increase linearly with increasing gadolinium concentrations. For the higher concentrations of gadolinium the magnetic susceptibility-temperature curve has a peak at 34 K, showing a magnetic field dependence of magnetic susceptibility at liquid helium temperature which would be expected for the case of a weak magnetic anisotropy in antiferromagnets.

The Magnetic Behaviors of Quasi-Two Dimensional Antiferromagnet (CH3NH3)2CuBr4

The temperature dependences of magnetic susceptibility and specific heat were measured for (CH 3 NH 3 ) 2 CuBr 4 . The phase transition to the antiferromagnetically ordered state was observed at 15.8 K. From the angle and field dependence of magnetic susceptibility, it was revealed that the preferred axis for the spins was c -axis in this compound. The origin of the anisotropy along c -axis was discussed qualitatively.

Field dependence of magnetic susceptibility of yttrium-gadolinium ferrites

Field dependence of magnetic susceptibility of yttrium-gadolinium ferrites

Quadratic integration: Theory and application to the electronic structure of platinum

In this paper we present a general computational technique for deriving fine histogram representations of singular k-dependent integrals for any crystalline solid. Detailed consideration is given to the errors involved in such integrals, and in their representations. Comparisons are made to previous work and the special advantage of each technique is emphasized. Applications of the quadratic (QUAD) technique are made to platinum using the combined interpolation scheme showing the total, band and basis function ( S-part) density of states. These densities of states are based on histograms of width 0.001 Ry, 1 000 000 Monte Carlo points in 1/48th of the Brillouin zone, and have an intrinsic accuracy of better than 1%. The extrinsic accuracy of the platinum band structure used here is somewhat poorer than 1%, and the special problems of materials with a steep derivative in the density of states at the Fermi energy is considered. Comparisons with the temperature and magnetic field dependent susceptibility and the specific heat data suggest that enhancement effects in platinum are small.

Field-dependent magnetic susceptibility in exchange enhanced Pd-Rh alloys at 200 kG

Abstract Direct observations of a field dependent magnetic susceptibility in strongly exchange enhanced Pd(Rh) alloys are presented. An exchange enhancement of about 9 is obtained (based on estimates of band parameters) for Pd 0.95 Rh 0.05 and a negative curvature of the density of states (at E F ) versus energy is deduced.

De Haas-van Alphen effect in aluminium and antimony.

THE de Haas – van Alphen effect (periodic field dependence of magnetic susceptibility) has been found in aluminium and antimony single crystals at 4.2° K. and lower temperatures. The effect depends in a complicated way on the direction of the magnetic field, and there are complicated modulation effects similar to those previously found in other metals1. Typical values of the period at 15,000 gauss are 400 gauss in aluminium and 270 gauss in antimony; the amplitude in both metals increases by a factor of order 4 when the temperature is reduced from 4.2° K. to 1.5° K. Aluminium is the first metal of cubic symmetry in which the effect has been found.