Showing papers on "Curie–Weiss law published in 1998"
TL;DR: In this article, the wave-number-dependent exchange constant matrix is obtained from spin-density-functional calculations with constrained moment directions, and the central assumption considers a fast electronic and a slow magnetic time scale, and postulates negligible correlation of fast motion between different ionic sites.
Abstract: The adiabatic theory of spin-density waves is developed on the basis of spin-density-functional theory. The wave-number-dependent exchange constant matrix is obtained from spin-density-functional calculations with constrained moment directions. The central assumption considers a fast electronic and a slow magnetic time scale, and postulates negligible correlation of the fast motion between different ionic sites. The parameter-free calculated magnon spectra for Fe, Co, and Ni are in excellent agreement with available experimental data. In the case of Fe, they show strong Kohn anomalies. Using Planck statistics at low temperature, the temperature dependence of the magnetization is well described up to half the Curie temperature. It is conjectured that correlated local-moment clusters survive the Curie transition. On this basis, calculated Curie temperatures are obtained within $10%$ deviation from experiment for Fe and Co, but $30%$ to low for Ni.
217 citations
TL;DR: In this paper, the authors presented x-ray magnetic circular dichroism (XMCD) measurements on single layers, bilayers, and trilayers consisting of Ni, Co, and Cu.
Abstract: We present x-ray magnetic circular dichroism (XMCD) measurements on single layers, bilayers, and trilayers consisting of Ni, Co, and Cu. Using XMCD sum rules, spin and orbital contributions to the total magnetic moment were determined for 2.1 ML Co and 4 ML Ni single layers on Cu(001). In accordance with theory for Co, both spin and orbital moments show an enhancement. In the case of Ni, both spin and orbital moments were reduced. The total magnetic moment of the 4 ML Ni film reduces by a factor of 2 as compared to the Ni bulk. The Curie temperature of both Ni and Co were found to reduce upon capping with Cu. In trilayers, the shape of the Ni magnetization curves were found to be influenced through exchange coupling due to the presence of Co.
83 citations
TL;DR: In this article, the Eu T In compounds were investigated by magnetic susceptibility measurements and 151 Eu Mossbauer spectroscopy, showing that the isomer shifts are linearly correlated with the closest Eu-Eu distance in the structure.
63 citations
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TL;DR: In this article, the magnetic properties of the lithium phthalocyanine radical are investigated for the x,α and β crystal structures via electron paramagnetic resonance (EPR), and different magnetic behaviours (susceptibility, line shape) are evidenced in PcLi powders and interpreted in terms of the molecular packing.
Abstract: The magnetic properties of the lithium phthalocyanine radical are investigated for the x,α and β crystal structures via electron paramagnetic resonance (EPR). Different magnetic behaviours (susceptibility, line shape) are evidenced in PcLi powders and interpreted in terms of the molecular packing. A Curie–Weiss susceptibility is observed for the α-phase with a mean-field temperature, TCW of ca. 4.5±1 K, whereas a two-component susceptibility must be considered for the x-phase (powders grown in acetonitrile) involving a Curie–Weiss contribution (TCWca. –3±1 K) and a thermally activated contribution with an activation energy Ea of ca. 0.04 eV. For the PcLi β structure two temperature domains can be distinguished: for T>50 K a Curie–Weiss susceptibility with a mean-field temperatureTCW of ca. –60±5 K is observed while for T<20 K a Curie–Weiss-like susceptibility withTCWca. –7±1 K dominates. The overall magnetic properties of the PcLi polymorphs are discussed in terms of McConnell’s mechanism for ferromagnetism and antiferromagnetism in solid free radicals. The magnetic properties of β-PcLi needles (magnetic susceptibility, anisotropy of spin diffusion) have been investigated. Adsorbed oxygen is shown to alter strongly the line shape, the linewidth and the g-factor anisotropy in β-PcLi crystallites and powders at temperatures below 55 K.
46 citations
TL;DR: In this article, the magnetic susceptibility is introduced as a thermodynamic quantity which requires a partial differentiation of the magnetization according to the applied field, which is called the differential magnetic susceptibility.
37 citations
TL;DR: In this article, the transport and magnetic properties of perovskite have been investigated and it was shown that transport occurs by means of coupling between localized levels, which is consistent with the adiabatic hopping of small polarons.
Abstract: The transport and magnetic properties of A-site-deficient perovskite have been investigated. The electrical conductivity displayed a thermally activated temperature dependence between 200 and 300 K with an activation energy of 0.17 eV. The thermopower measured over a similar temperature range showed little temperature dependence, indicating that transport occurs by means of coupling between localized levels. Analysis of the susceptibility based on the Curie-Weiss law indicated that the Curie constant of the 4f spin of Ce is approximately 40% smaller than that of the free ion due to the crystalline-electric-field effects. Unlike shows a very simple temperature dependence of its magnetic susceptibility and there is no evidence for the onset of weak ferromagnetism at any temperature. These results are shown to be consistent with transport by means of adiabatic hopping of small polarons.
36 citations
Journal Article•
TL;DR: The role of the JT polaron in determining the electronic and magnetic properties above T c is discussed in this paper, where phase transitions at T c (=245 K), 345 K and 545 K are discussed.
Abstract: Resistivity (15-710 K), magnetization (80-723 K), and calorimetric (200-623 K) measurements on La 0.7 Ca 0.3 MnO 3 have shown evidence for the formation of Jahn-Teller (JT) polarons below ∼545 K. Above 560 K, activated conduction with E a = 0.05 eV is observed and X -1 (T) shows Curie-Weiss behaviour. Over the temperature range 270-340 K, the conductivity follows Mott's VRH model and X -1 (T) provides evidence of the formation of spin clusters. Calorimetric study shows phase transitions at T c (=245 K), 345 K and 545 K. The role of the JT polaron in determining the electronic and magnetic properties above T c is discussed.
36 citations
35 citations
TL;DR: In this paper, the infinite-dimensional spin-one-half Falicov-Kimball model in an external magnetic field is solved exactly, and the magnetic susceptibility in zero field and the magnetization as a function of the field strength are calculated.
Abstract: The infinite-dimensional spin-one-half Falicov-Kimball model in an external magnetic field is solved exactly. We calculate the magnetic susceptibility in zero field, and the magnetization as a function of the field strength. The model shows an anomalous magnetic response from thermally excited local moments that disappear as the temperature is lowered. We describe possible real materials that may exhibit this kind of anomalous behavior.
TL;DR: In this paper, the magnetic properties of Ga1−xMnxSe, which represent a new class of diluted magnetic semiconductors based on a III-VI semiconductor, were investigated.
Abstract: We have investigated the magnetic properties of Ga1−xMnxSe, which represent a new class of diluted magnetic semiconductors based on a III-VI semiconductor. These are layered materials; however the local environment is tetrahedral as in the II-VI materials. In contrast to the II-VI semiconductors, the Mn substitutional atoms have direct bonds to three Se atoms and to either a Ga or Mn atom. This leads to a complex temperature dependent magnetization. In fields of 100 G and below, a broad peak is observed in the magnetization centered at 160 K. In addition, a sharp change in magnetization is observed at 119 K. In a field of 100 G, the peak has a magnitude of 3×10−5 emu/g above the background of 7×10−5 emu/g. With increasing magnetic fields, these features are broadened which is suggestive of some type of short-range antiferromagnetic ordering. At 5 K we observe a magnetization which increases linearly with field up to 6 T similar to the Van Vleck paramagnetic behavior observed in the Fe substituted II-VI se...
TL;DR: In this paper, the authors studied a dynamics for the magnetization of the random field Curie-Weiss model and gave asymptotic estimates on the speed of convergence to equilibrium.
Abstract: We study a dynamics for the magnetization of the random field Curie–Weiss model. A metastable behavior is exhibited and asymptotic estimates on the speed of convergence to equilibrium are given. The results are given almost surely and in law with respect to the realizations of the random magnetic fields.
TL;DR: In this paper, the magnetic susceptibility and X-ray photoelectron spectra of YMn4Al8 and CeMn6Al6 and of the reference compounds are reported, and the occurrence of a Mn moment in the investigated compounds is strongly correlated with the critical value d ≥ 2.6 A of the Mn-Mn distance below which the Mn moment collapses.
TL;DR: Srir39Co12N31 has a unique structure incorporating coalt in linear coordination as isolated nitridometalate ions as mentioned in this paper, and all cobalt atoms are crystallographically equivalent, existing with a formal mixed valence of CoI and CoII.
TL;DR: In this paper, it was shown that the semiconductor-to-metal transition occurring at 2 GPa in this compound is accompanied by the appearance of strong ferromagnetic exchange interactions producing a Curie temperature as high as 14 K. This behavior is characteristic for the incipient mixed-valence regime just above the transition pressure and traced back to the release of a small concentration of free charge carriers in the material.
Abstract: Neutron diffraction experiments on TmTe at pressures up to 7 GPa are reported. The semiconductor-to-metal transition occurring at 2 GPa in this compound is accompanied by the appearance of strong ferromagnetic exchange interactions producing a Curie temperature as high as 14 K. This behavior is characteristic for the incipient mixed-valence regime just above the transition pressure and traced back to the release of a small concentration of free charge carriers in the material. The steep decrease of both the Curie temperature and ordered magnetic moment occurring at higher pressures emphasizes the role of Kondo fluctuations, and raises the interesting possibility that a quantum critical transition to a non-magnetic ground state of mixed-valence Tm might take place around 6 GPa.
TL;DR: In this article, a cubic MgCu2-type structure (space group of Fd3m) with lattice constants of a=0.7425 nm was studied for the first time.
Abstract: SmFe2 crystals were grown by the self-flux method using Sm as a flux, and the crystallographic and magnetic properties of the crystal were studied for the first time. SmFe2 crystallizes in a cubic MgCu2-type structure (space group of Fd3m) with lattice constants of a=0.7425 nm. Saturation magnetization MS at 5 K and 300 K and the Curie temperature of SmFe2 are 64.4 emu/g, 59.8 emu/g, and 669 K, respectively. The easy-direction of the magnetization is parallel to the [110] direction of the cubic crystal at 300 K, but it changes to the [111] direction at about 195 K.
Journal Article•
TL;DR: In this paper, the spin-fluctuation method developed by the authors in a previous paper for calculating the average and local magnetic characteristics of ferromagnetic metals at finite temperatures is extended to the case of dynamic nonlocal fluctuations.
Abstract: The spin-fluctuation method developed by the authors in a previous paper for calculating the average and local magnetic characteristics of ferromagnetic metals at finite temperatures is extended to the case of dynamic nonlocal fluctuations. This new method is based on a self-consistent quadratic approximation to the free energy of electrons in a random exchange field. The model parameters are the electron density of states and the atomic magnetic moment at T = 0 for a specific metal. The magnetization, the Curie temperature, the local magnetic moment, and the uniform and local susceptibilities are calculated for ferromagnetic and paramagnetic states of iron. The results are in agreement with experimental data over a wide range of temperatures. The calculated Curie temperature is close to the observed one: T C dyn = 1.2T c . The paramagnetic susceptibility follows the Curie-Weiss law, from which the effective magnetic moment is found to be m eff dyn = 3.50 μ B and the paramagnetic Curie point θ C dyne = 1.1 T c .
TL;DR: In this paper, magnetic measurements of Ni-oxide-based thin films were performed at low temperatures using SQUID technology, and they exhibited a well-defined Curie Weiss behavior with a transition temperature that was depressed by proton extraction.
TL;DR: In this paper, the magnetic moments are estimated to be 0.72 (1) and 0.43(1)μBon on the Ti(III and Sm(III) sublattices, respectively.
TL;DR: In this article, the C15 cubic Laves phase structure and an estimated density of 5.21 g/cm3 has been synthesized at 8.0 GPa pressure and magnetization measurements showed that the compound CaCo2 is a ferromagnet with Curie temperature 528 K and magnetic moment per Co atom 1.75 μB at T = 4.2 K.
Abstract: The compound CaCo2 with the C15 cubic Laves phase structure and an estimated density of 5.21 g/cm3 has been synthesized at 8.0 GPa pressure. Magnetization measurements showed that the compound CaCo2 is a ferromagnet with Curie temperature 528 K and magnetic moment per Co atom 1.75 μB at T=4.2 K. LMTO calculations of the electronic band structure showed that CaCo2 forms as a result of an s-d electronic transition of Ca and in the ground state it is a ferromagnet with a high magnetic moment per Co atom.
TL;DR: In this article, the optical and magnetic properties of one-dimensional polymeric Ln(Cl 3 CCOO) 3 ·2H 2 O (Ln=Nd, Eu, Dy) ( I ) and heteronuclear CuNd 2 (Cl 3CCOO) 8 ⋅6H 2O ( II ) single crystals were investigated in the 4.2-293-k temperature range and discussed on the basis of X-ray data.
TL;DR: In this paper, the inverse susceptibilities of the monopnictides and monochalcogenides of the light rare earths plotted vs. temperature flatten off at high temperatures.
TL;DR: In this article, the electrical resistivity and the magnetism of heavy-rare-earth-based Zn 60 Mg 30 Ho 10 F-type icosahedral quasicrystals in the temperature region between 2.5 and room temperature below 80 kOe in magnetic field were investigated.
TL;DR: In this article, the crystal structures of the YbAg 2 In 4 and CaAg 2 IN 4 compounds were determined by means of the single crystal method (DARTCH-1 automatic diffractometer, graphite-monochromatized Mo Kα radiation, θ −2 θ scan mode).
TL;DR: In this article, the magnetic properties of the Curie point were investigated in order to obtain information about the magnetic moment of CuCr 2 Se 4 and the changes in the curie point.
TL;DR: In this paper, the synthesis of Li6CoO4, Na4CoO3, and Na10Co4O9 and refinements of the crystal structures of the two sodium compounds are reported.
Abstract: The synthesis of Li6CoO4, Na4CoO3, and Na10Co4O9 and the refinements of the crystal structures of the two sodium compounds are reported. The physical properties of these materials have been studied by measuring the absorption spectra and the susceptibility. An interpretation of these data is presented for the tetrahedral [CoO4]6- and trigonal planar [CoO3]4- complexes in terms of the angular-overlap model.
TL;DR: In this article, a series of oxide glasses rich in Fe 2+ and Fe 3+ with their various molar ratio has been synthesized, and the magnetic behaviors have been studied by static magnetization and ESR experiments.
Abstract: A series of oxide glasses rich in Fe 2+ and Fe 3+ with their various molar ratio has been synthesized, and the magnetic behaviors have been studied by static magnetization and ESR experiments. Near room temperature, superparamagnetic behavior is caused by deposited fine (40–50 A) clusters of iron-oxides. At lower temperatures, though, we observe drastic descending shift of the field for ESR as well as ferromagnetic Curie-Weiss law in the susceptibility. We interpret these behaviors consistently by a classical model, taking into account only an effective interaction between the clusters and the magnetic matrix region. For the glasses of moderate oxidation grades (molar ratio of Fe 2+ to total Fe is in 0.39–0.66), each shifting ESR field also shows a peak anomaly near 100 K caused by Verwey transition of magnetite clusters. Verwey transition is observed evidently for the super fine clusters owing to the protection against oxidation in the glasses.
TL;DR: In this article, the external magnetic field effects on the photoinduced magnetization of a cobalt iron cyanide, K 0.4Co1.3[Fe(CN)6]·5H2O was studied.
Abstract: We studied the external magnetic field effects on the photoinduced magnetization of a cobalt iron cyanide, K0.4Co1.3[Fe(CN)6]·5H2O. Photoinduced magnetization value was increased ca. 20 % at maximum under the magnetic field of 50000 G at 5 K. In addition, in the ferrimagnetic region (T < Tc = 26 K), the external magnetic field accelerated the rate of photoinduced spin generation. Those data suggest that external magnetic field increases magnetic interaction between the excited state and spin clusters.
TL;DR: In this article, the authors consider a mean-field continuum model of classical particles with Ising or Heisenberg spins and show that a feedback between these forces gives rise to a first-order phase transition with simultaneous jumps of particle density and magnetization per particle.
Abstract: We consider a mean-field continuum model of classical particles in Rd with Ising or Heisenberg spins. The interaction has two ingredients, a ferromagnetic spin coupling and a spin-independent molecular force. We show that a feedback between these forces gives rise to a first-order phase transition with simultaneous jumps of particle density and magnetization per particle, either at the threshold of ferromagnetic order or within the ferromagnetic region. If the direct particle interaction alone already implies a phase transition, then the additional spin coupling leads to an even richer phase diagram containing triple (or higher order) points.