Showing papers on "Curie–Weiss law published in 2005"
TL;DR: In this article, a simple concept was used for a systematic search for materials with high spin polarization, based on two semi-empirical models: the Slater-Pauling rule was used to estimate the magnetic moment and the second model was found particularly for Heusler compounds when comparing their magnetic properties.
Abstract: In this work a simple concept was used for a systematic search for materials with high spin polarization It is based on two semiempirical models First, the Slater-Pauling rule was used for estimation of the magnetic moment This model is well supported by electronic structure calculations The second model was found particularly for ${\mathrm{Co}}_{2}$ based Heusler compounds when comparing their magnetic properties It turned out that these compounds exhibit seemingly a linear dependence of the Curie temperature as function of the magnetic moment Stimulated by these models, ${\mathrm{Co}}_{2}\mathrm{FeSi}$ was revisited The compound was investigated in detail concerning its geometrical and magnetic structure by means of x-ray diffraction, x-ray absorption, and M\"ossbauer spectroscopies as well as high and low temperature magnetometry The measurements revealed that it is, currently, the material with the highest magnetic moment $(6{\ensuremath{\mu}}_{B})$ and Curie temperature (1100 K) in the classes of Heusler compounds as well as half-metallic ferromagnets The experimental findings are supported by detailed electronic structure calculations
550 citations
TL;DR: In this paper, the Curie temperature in the ferromagnetic Heusler alloy has been studied theoretically within the framework of the density functional theory and the exchange parameters are calculated based on the frozen-magnon approach.
Abstract: The pressure dependence of electronic structure, exchange interactions, and Curie temperature in the ferromagnetic Heusler alloy ${\mathrm{Ni}}_{2}\mathrm{MnSn}$ has been studied theoretically within the framework of the density-functional theory. The calculation of the exchange parameters is based on the frozen-magnon approach. The Curie temperature ${T}_{c}$ is calculated within the mean-field approximation by solving the matrix equation for a multisublattice system. In agrement with experiment the Curie temperature increased from 362 K at ambient pressure to 396 K at 12 GPa. Extending the variation of the lattice parameter beyond the range studied experimentally, we obtained nonmonotonic pressure dependence of the Curie temperature and metamagnetic transition. We relate the theoretical dependence of ${T}_{c}$ on the lattice constant to the corresponding dependence predicted by the empirical interaction curve. The Mn-Ni atomic interchange observed experimentally is simulated to study its influence on the Curie temperature.
132 citations
TL;DR: The bulk magnetic susceptibility chi(T,B) of YbRh(2)(Si(0.95)Ge( 0.05))(2) has been investigated close to the field-induced quantum critical point at B(c) = 0.3 K as mentioned in this paper.
Abstract: The bulk magnetic susceptibility chi(T,B) of YbRh(2)(Si(0.95)Ge(0.05))(2) has been investigated close to the field-induced quantum critical point at B(c) = 0.027 T. For B < or= 0.05 T a Curie-Weiss law with a negative Weiss temperature is observed at temperatures below 0.3 K. Outside this region, the susceptibility indicates ferromagnetic quantum critical fluctuations, chi(T) proportional, variantT-0.6 above 0.3 K. At low temperatures the Pauli susceptibility follows chi(0) proportional, variant(B-B(c))(-0.6) and scales with the coefficient of the T(2) term in the electrical resistivity. The Sommerfeld-Wilson ratio is highly enhanced and increases up to 30 close to the critical field.
117 citations
TL;DR: In this article, the temperature dependence of the uniform susceptibility of spin-half quantum antiferromagnets on spatially anisotropic triangular lattices, using high-temperature series expansions, was investigated.
Abstract: We present the temperature dependence of the uniform susceptibility of spin-half quantum antiferromagnets on spatially anisotropic triangular lattices, using high-temperature series expansions. We consider a model with two exchange constants J1 and J2 on a lattice that interpolates between the limits of a square lattice (J1=0), a triangular lattice (J2=J1), and decoupled linear chains (J2=0). In all cases, the susceptibility, which has a Curie-Weiss behavior at high temperatures, rolls over and begins to decrease below a peak temperature Tp. Scaling the exchange constants to get the same peak temperature shows that the susceptibilities for the square lattice and linear chain limits have similar magnitudes near the peak. Maximum deviation arises near the triangular-lattice limit, where frustration leads to much smaller susceptibility and with a flatter temperature dependence. We compare our results to the inorganic materials Cs2CuCl4 and Cs2CuBr4 and to a number of organic molecular crystals. We find that the former (Cs2CuCl4 and Cs2CuBr4) are weakly frustrated and their exchange parameters determined through the temperature dependence of the susceptibility are in agreement with neutron-scattering measurements. In contrast, the organic materials considered are strongly frustrated with exchange parameters near the isotropic triangular-lattice limit.
92 citations
TL;DR: In this paper, the authors reported detailed dielectric studies carried out on barium strontium titanate (BST) (80:20) and (60:40) compositions.
78 citations
TL;DR: Vaitheeswaran et al. as discussed by the authors measured Re 5d spin and orbital magnetic moments in the ferrimagnetic double perovskite Sr2CrReO6 by x-ray magnetic circular dichroism at the L2,3 edges.
Abstract: We have measured Re 5d spin and orbital magnetic moments in the ferrimagnetic double perovskite Sr2CrReO6 by x-ray magnetic circular dichroism at the L2,3 edges In fair agreement with recent band structure calculations [G Vaitheeswaran, V Kanchana, and A Delin, Appl Phys Lett 86, 032513 (2005)], at the Re site a large 5d spin magnetic moment of −068μB and a considerable orbital moment of +025μB have been detected We found that the Curie temperature of the double perovskites A2BB′O6 scales with the spin magnetic moment of the “nonmagnetic” B′ ion
61 citations
TL;DR: In this article, the effect of gadolinium content as well as temperature 123-433 K on resonance signals have been investigated, and the theoretical values of optical basicity (Λth) of the glasses have been evaluated.
Abstract: Glass systems of composition 85 Li2B4O7+(15−x) TeO2+x Gd2O3 ( x = 0 , 1, 2, 3, 4 and 5 mol%) and 80 Li2B4O7+10 PbO+8 TeO2+2 Gd2O3 have been studied by using electron paramagnetic resonance (EPR). The EPR spectra indicate Gd3+ ions located at three types of sites randomly distributed in the host glass. The spectra exhibits three broad EPR signals at g ≈ 2.0 , g ≈ 2.8 and g ≈ 5.4 are attributed to Gd3+ ions located at sites with weak, intermediate and strong cubic symmetry fields respectively. In principle these sites may be of network forming and network modifying type. Ionic radius considerations suggest that gadolinium ions cannot substitute the much smaller boron ions and thus only the network modifier site is acceptable. The effect of gadolinium content as well as temperature 123–433 K on resonance signals have been investigated. The number of spins (N) participating in resonance and its paramagnetic susceptibility ( χ ) for g ≈ 5.4 resonance line have been calculated as a function of Gd content and temperature. It is observed that N and χ increase with x. A linear relationship was established between log N and 1 / T and the activation energy was calculated from the graph. From the graph the Curie constant (C) and Curie temperature ( θ ) have been evaluated. The temperature dependence of inverse magnetic susceptibility ( 1 / χ ) displays Curie–Weiss type of magnetic behaviour. The theoretical values of optical basicity (Λth) of the glasses have also been evaluated.
49 citations
TL;DR: In this article, the interatomic exchange interactions and Curie temperatures in half-metallic semi-Heusler compounds NiCrZ (Z=P, Se, Te) and NiVAs were studied within the framework of density functional theory.
Abstract: We study the interatomic exchange interactions and Curie temperatures in half-metallic semi-Heusler compounds NiCrZ (Z=P, Se, Te) and NiVAs. The study is performed within the framework of density functional theory. The calculation of exchange parameters is based on the frozen-magnon approach. It is shown that the exchange interactions in NiCrZ vary strongly depending on the Z constituent. The Curie temperature is calculated within mean field and random phase approximations. The difference between two estimated values is related to the properties of the exchange interactions. The predicted Curie temperatures of all four systems are considerably above room temperature. The relation between half-metallicity and the value of the Curie temperature is discussed. The combination of a high spin polarization of charge carriers and a high Curie temperature makes these Heusler alloys interesting candidates for spintronics applications.
42 citations
TL;DR: In this article, the magnetic properties of an insulating cubic compound Cu3TeO6 studied by ac and dc susceptibility, torque magnetometry and neutron powder diffraction were reported.
Abstract: We report on the magnetic properties of an insulating cubic compound Cu3TeO6 studied by ac and dc susceptibility, torque magnetometry and neutron powder diffraction. A novel three-dimensional magnetic lattice composed of almost planar regular hexagons of Cu2+ S = 1/2 spins is present in Cu3TeO6. The magnetic susceptibility in the paramagnetic state obeys the Curie–Weiss law in the 200–330 K regime with ΘCW = −148 K and at TN = 61 K system undergoes an antiferromagnetic phase transition. Above TN the susceptibility is isotropic. Below TN a large anisotropy develops in fields H≥500 Oe. Torque measurements reveal the presence of antiferromagnetic domains below TN. In a rather low magnetic field ( Oe) switching of domains is observed. The dynamics related to movement of domain walls is very slow at low temperatures (of the order of 102 s) and interferes with all torque measurements. The presence of domains is a consequence of the symmetry of the underlying magnetic lattice. Neutron powder diffraction reveals that antiferromagnetic long-range order is associated with the wavevector . The dominant component of the magnetic moment is along one of the space diagonals of the cubic unit cell, but it is not possible to resolve whether the structure is collinear or canted.
37 citations
TL;DR: In this article, the magnetization properties of amorphous Fe90−xMnxZr10 (x=8 and 10) alloys were measured at temperatures above the Curie temperature in the paramagnetic region.
Abstract: The magnetization behaviors have been measured for amorphous Fe90−xMnxZr10 (x=8 and 10) alloys. The Curie temperature is decreased from 210Kto185K with increasing Mn concentration (x=8 to x=10). The magnetization measurements were conducted at temperatures above the Curie temperature in the paramagnetic region. In both samples, the magnetic properties showed superparamagnetic behavior above Tc where the mean magnetic moment of the superparamagnetic spin clusters decreased with increasing temperature. A large magnetic entropy change ΔSM, which is calculated from H vs M curves associated with the ferromagnetic-paramagnetic transitions in amorphous, has been observed. The maximum ΔSM of Fe82Mn8Zr10 is 2.87J∕kgK at 210K for an applied field of 5T. The peak of magnetic entropy change was observed at the Curie temperature. The ΔSM decreases with increasing Mn concentration to 2.33J∕kgK.
36 citations
TL;DR: In this article, the magnetic and magnetocaloric properties of polycrystalline perovskite La 0.70 Ca 0.20 Sr 0.10 MnO 3 were investigated.
TL;DR: In this article, the curie temperature of Gd (1− x ) In x ( x ǫ = 0.01, 0.02 and 0.03) alloys has been investigated.
TL;DR: In this article, a new compound UPd2Sb was prepared and studied by means of X-ray diffraction, magnetization, electrical resistivity, magnetoresistivity, thermoelectric power and specific heat measurements.
TL;DR: The La0.8Sr0.2MnO3 compound presented a ferromagnetic paramagnetic transition around room temperature to which a reasonably high magnetocaloric effect is associated, turning this material of interest for application in magnetic refrigeration as discussed by the authors.
Abstract: The La0.8Sr0.2MnO3 compound presents a ferromagnetic paramagnetic transition around room temperature to which a reasonably high magnetocaloric effect is associated, turning this material of interest for application in magnetic refrigeration. We synthesized this compound in fiber single crystalline form by the Laser Heated Pedestal Growth method. The sample was characterized by x-ray diffraction and magnetic measurements as a single phase and with the required magnetic properties. We measured the magnetic properties and the magnetocaloric effect under hydrostatic pressure for pressures up to 6 kbar as a function of temperature. Our results indicate that the Curie temperature increases with pressure while the low temperature transition from the orthorhombic to the rhombhoedral structures decreases as pressure increases. This is in close agreement with the literature. Measurement of the magnetocaloric effect at the high temperature transition indicates that the peak of the effect follows the trend of the Cur...
TL;DR: In this article, it was shown that CoVSb is not a half-metallic ferromagnet as predicted by band theory, and that the magnetic properties are not dependent upon the nature of the atomic order in the C1b lattice.
Abstract: Magnetization and neutron powder diffraction measurements have been carried out on CoVSb. Both the transport and magnetic properties are predicted by band theory to depend upon the nature of the atomic order in the C1b lattice. Calculations in which the cobalt atoms occupy the (4b) site predict half-metallic behaviour and a ground state moment of ~1 μB per formula unit with 1.19 μB on the vanadium atoms and −0.19 μB on the cobalt atoms. However, calculations in which the Sb or V atoms occupy the (4b) site predict larger moments, ~0.7 μB, on the cobalt atoms, and either zero or a negative moment on the vanadium atoms. In contrast, the magnetization measured in fields of up to 5.5 T is small, amounting to a ferromagnetic moment per formula unit of 0.17 μB at 2 K. Both the field dependence of the magnetization in the ordered phase below Tc~48 K and the large effective moment obtained from the Curie–Weiss susceptibility above Tc are consistent with weak itinerant ferromagnetism. Confirmation of the small ground state moment and hence the absence of any significant moment on the vanadium atoms was obtained from neutron powder diffraction measurements, which also enabled the crystallographic structure to be determined as C1b with the cobalt atoms occupying the (4b) sites. The results show that CoVSb is not a half-metallic ferromagnet as predicted by band theory.
TL;DR: In this article, the low-temperature heat capacity properties characterize Ce2Au2Cd as a heavy fermion material with an electronic specific heat coefficient (gamma) = 807(5) mJ/mol K2 as compared to La2a2cd with gamma = 6 (5)mJ/m K2.
Abstract: La2Au2Cd and Ce2Au2Cd were prepared from the elements by reactions in sealed tantalum tubes in a water-cooled sample chamber of an induction furnace. These intermetallics crystallize with the tetragonal Mo2FeB2 type, space group P4/mbm. While La2Au2Cd is Pauli paramagnetic, Ce2Au2Cd shows Curie-Weiss behaviour above 100 K with an experimental magnetic moment of 2.41(2) muB/Ce atom, indicating trivalent cerium. Antiferromagnetic ordering is detected for Ce2Au2Cd at 5.01(2) K and magnetization measurements reveal a metamagnetic transition at 3 K at a critical field of around 20 kOe with a saturation moment of 1.50(2)muB/Ce atom at 80 kOe. The low-temperature heat capacity properties characterize Ce2Au2Cd as a heavy fermion material with an electronic specific heat coefficient (gamma) = 807(5) mJ/mol K2 as compared to La2Au2Cd with gamma = 6(5) mJ/mol K2.
TL;DR: In this paper, a single phase MnB alloy has been fabricated and characterized and the magnetic properties have been studied using superconducting quantum interference device and vibrating sample magnetometer over a broad temperature range.
Abstract: Manganese is a common dopant to achieve dilute magnetic semiconductors. Most magnetic semiconductors are hole-type and the Curie temperature is critically depending on the holes concentration. Boron can be used to increase the holes concentration and enhance the Curie temperature. In systems with both Mn and B dopants, one must consider the magnetic properties of MnB. In this study, single phase MnB alloy has been fabricated and characterized. Magnetic properties have been studied using superconducting quantum interference device and vibrating sample magnetometer over a broad temperature range. Very high magnetization of about 113emu∕g at room temperature has been observed, which is much higher than previous reports. The Curie temperature is around 306 °C, similar to previously reported value.
TL;DR: In this paper, the results indicate an inhomogeneous distribution of Ca2+ ions in a microscopic local scale, and existence of phase separation into a hole-rich ferromagnetic regions and a holepoor host matrix.
TL;DR: In this article, the magnetic properties of the Laves phase compound GdNi2 were investigated and analyzed in detail by employing molecular-field analysis both the temperature dependence of the magnetization and the Curie-Weiss (C-W) law-like linear relationship of inverse susceptibility were reproduced in terms of a two-sublattice model.
Abstract: Magnetization and inverse susceptibility of the Laves phase compound GdNi2 were investigated and analyzed in detail by employing molecular-field analysis Both the temperature dependence of the magnetization and the Curie–Weiss (C–W) law-like linear relationship of inverse susceptibility are reproduced in terms of a two-sublattice model and it is seen that the magnetic structure of GdNi2 is ferrimagnetic and Ni in GdNi2 retains a magnetic moment of about 024μB
TL;DR: In this paper, the average structure model of Pb3V(PO4)3 was refined using X-ray single crystal data (a = 10.127 ( 1 ) A, S.G. I 4 ¯ 3 d, Z = 4 ).
TL;DR: In this article, the temperature dependences of the susceptibility of all samples exhibit a paramagnetic behavior and the χ-T curves were fitted by the Curie-Weiss law χ ǫ = C /(T ǔ − Θ ) above 2.05.
TL;DR: In this paper, the magnetic and galvanomagnetic properties of single crystals of a new dilute magnetic semiconductor p-Sb2−xCrxTe3 (x = 0, 0.0115,0.0215) are investigated in a temperature range of 1.7-300 K.
Abstract: Magnetic and galvanomagnetic properties of single crystals of a new dilute magnetic semiconductor p-Sb2−xCrxTe3 (x = 0, 0.0115, 0.0215) are investigated in a temperature range of 1.7–300 K. A ferromagnetic phase with a Curie temperature of TC ≈ 5.8 (x = 0.0215) and 2.0 K (x = 0.0115) is detected. The easy magnetization axis is parallel to the C3 crystallographic axis. Analysis of the Shubnikov-de Haas effect observed in these crystals in strong magnetic fields leads to the conclusion that the hole concentration decreases as a result of doping with Cr. Negative magnetoresistance and the anomalous Hall effect are observed in Cr-doped samples at liquid helium temperature.
TL;DR: The magnetic properties of the ternary intermetallic compounds Sm 3 Ag 4 Sn 4 and Gd 3 Ag4 Sn 4 were investigated in this article, where they were shown to display antiferromagnetic ordering at low temperatures.
TL;DR: In this article, the magnetic properties and magnetocaloric effect of Gd(FexAl1-x)(2) compounds with Laves-phase structure were investigated, and the temperature dependence of the magnetization of these compounds was measured to determine their Curie temperatures, while the change of the magnetic entropy was calculated from magnetization curves at different temperatures.
Abstract: The magnetic properties and magnetocaloric effect of Gd(FexAl1-x)(2) compounds with Laves-phase structure have been investigated. The temperature dependence of the magnetization of these compounds was measured to determine their Curie temperatures, while the change of the magnetic entropy was calculated from magnetization curves at different temperatures. Fe substitution for Al at first decreases the Curie temperature, and increases the change of the magnetic entropy. The largest value for the magnetic entropy vertical bar Delta S(M)vertical bar = 8.4J/kg/K, is achieved for Gd(Fe0.15Al0.85)(2), which has the lowest Curie temperature. The magnetic entropy decreases with further increase of the Fe content, accompanied by an increase of the Curie temperature. (c) 2005 Elsevier B.V. All rights reserved.
TL;DR: The compound Ca14MnP11 crystallizes in the Ca14AlSb11 structure type with the tetragonal space group I 4 1 / acd (Z = 8 ) and lattice parameters of a = 153255 ( 7 ) A, c = 207565 ( 9 ) at 90 K as discussed by the authors.
TL;DR: In this paper, the effects of substitution of Cu for Ni in NiMnSb alloys with the substitution of Ni for Ni were investigated and the Curie temperature and susceptibility for different Cu compositions were measured on SQUID.
TL;DR: In this article, the properties of R2BaPdO5 (R = La, Pr, Nd, Sm, Eu, Gd, Dy, Ho) were investigated.
TL;DR: In this article, a GMR ratio of 4% and magnetization perpendicular to the film planes were fabricated with a large coercivity (12 kOe) of the free layer (TbCo∕Co) guarantees the thermal stability at room temperature, while that of the pinned layer keeps unchanged at the temperatures between Curie temperatures of two layers.
Abstract: Giant magnetoresistance (GMR) samples composed of TbCo∕Co∕Cu∕Co∕TbFeCo layers were fabricated with a GMR ratio of 4% and magnetization perpendicular to the film planes. A large coercivity (12 kOe) of the free layer (TbCo∕Co) guarantees the thermal stability at room temperature. A lower Curie temperature of the free layer than that of the pinned layer (Co∕TbFeCo) enables us to switch the magnetization of the free layer by thermally assisted writing while that of the pinned layer keeps unchanged at the temperatures between Curie temperatures of two layers. When the sample was heated up to 180 °C, the required switching field was only 10 Oe.
TL;DR: In this article, the main feature of both crystal structures are CuO2 chains built up from planar, edge-sharing CuO4 squares, and the analysis of the CuO bond lengths, the valence states of either +2 or +3 can be unambiguously assigned to each copper atom.