Showing papers on "Curie–Weiss law published in 1985"
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04 Sep 1985TL;DR: In this paper, a general theory of spin fluctuations and thermodynamical properties of itinerant electron magnets is developed, interpolating between the weakly and strongly ferromagnetic limits, and a unified expression is given for the Curie temperature and the physical meaning of the curie-Weiss magnetic susceptibility is discussed.
Abstract: A general theory of spin fluctuations and thermodynamical properties of itinerant electron magnets is developed, interpolating between the weakly and strongly ferromagnetic limits. A unified expression is given for the Curie temperature and the physical meaning of the Curie-Weiss magnetic susceptibility is discussed. As new phenomena derived from this theory the temperature-induced local magnetic moments as observed in CoS2, CoSe2, etc. and peculiar magnetic and thermal properties of nearly ferromagnetic semiconductors such as FeSi are discussed.
1,321 citations
TL;DR: In this paper, the authors present a quantitative model for the magnetic equation of state of nearly or weakly ferromagnetic metals at low temperatures which includes corrections to conventional Stoner theory arising from enhanced fluctuations in the local magnetisation.
Abstract: The authors present a quantitative model for the magnetic equation of state of nearly or weakly ferromagnetic metals at low temperatures which includes corrections to conventional Stoner theory arising from enhanced fluctuations in the local magnetisation. The model takes account of both longitudinal and transverse fluctuations in terms of four physically transparent parameters which may be determined independently from the equation of state in the T=0 limit and from inelastic neutron scattering, or calculated directly from a semi-empirical band structure model near the Fermi level fitted for example to experimental Fermi surface areas. For parameters of the same order of magnitude as those recently determined in the weakly spin-polarised metal Ni3Al, the model yields approximately a quadratic temperature dependence of the spontaneous magnetisation over a wide range well below the Curie temperature (Tc), a nearly linear inverse susceptibility well above Tc, and nearly linear magnetic isotherms (Arrott plots) at high magnetic fields. These results are qualitatively consistent with the behaviour observed in many magnetic metals near the ferromagnetic instability at low temperatures. For Ni3Al the model yields good quantitative agreement with experiment for the magnitude of the Curie temperature Tc, for the ratio peff/p0 of the high- to low-temperature effective magnetic moments, and for the coefficient of the quadratic (T2) variation of the magnetisation with temperature well below Tc, without the use of any free adjustable parameters. Finally the authors show that the model also provides a good quantitative description of the paramagnetic susceptibility and transition temperature of the more complex magnetic system MnSi, the only other unsaturated magnetic metal for which all of the microscopic parameters are well known.
337 citations
74 citations
TL;DR: Magnetization measurements of the system Ce(Fe 1- x Al x ) 2 for x ⩽ 0.20 show that the substitution of Fe by Al in CeFe 2 has not a simple dilution effect.
54 citations
TL;DR: In this paper, the authors studied the temperature dependence of the time decay of the magnetization, dM/d lnt, in magnetic tapes as a function of reversal magnetic field, following an initial applied saturating field.
Abstract: We have studied the temperature dependence of the time decay of the magnetization, dM/d lnt, in magnetic tapes as a function of reversal magnetic field, following an initial applied saturating field. We find the maximum decay rate occurs at the coercive field for all temperatures from 300 down to 6 K. Theoretical results and the available experimental data for studies in rock magnetism and ferromagnetic materials suggest the maximum magnetization decay should be proportional to the temperature. While we do find a linear temperature dependence, the data do not extrapolate to zero at T = 0 K, but surprisingly imply a finite value.
43 citations
TL;DR: In this article, the magnetic susceptibilities of R2Fe14B compounds were determined from the Curie temperature (TC) up to a characteristic temperature Tt. Tt = 830, 920, and 960 K for R = Pr, Nd, Dy, or Er, respectively.
Abstract: R2Fe14B compounds, R = Pr, Nd, Dy, or Er, were prepared from high purity rare earths obtained from the Ames Laboratory. The magnetic properties of these and related systems with other rare earths are under investigation in our laboratories. In the present study magnetic susceptibilities were determined from the Curie temperature (TC) (556–596 K) up to a characteristic temperature Tt. Above Tt the susceptibility was observed to increase sharply and to become history‐dependent, suggesting sample decomposition or a phase change. Tt = 830, 920, and 960 K for R = Pr, Nd, and Er, respectively. Curie–Weiss behavior is observed for the Pr and Nd compounds but not for Dy2Fe14B and Er2Fe14B. The susceptibility of the latter material follows the hyperbolic form described by Neel, i.e., 1/χ=1/χ0+T/C−σ/(T−θ). For R=Pr and Nd, near TC χ follows the expression χαt−γt=(T−TC)T−1C]. γ=1.37 for R=Pr and 1.41 for R = Nd. The iron paramagnetic moments are 4.02, 4.06, 4.09, and 4.10 μB for Pr2Fe14B and Nd2Fe14B, Dy2Fe14B and E...
35 citations
TL;DR: Analysis of the magnetic susceptibility data in terms of crystalline electric fields shows that the ground state of the Tm/sup 3 +/ ion is nonmagnetic which, therefore, does not affect the superconducting state.
Abstract: Magnetic susceptibility and /sup 119/Sn Moessbauer studies have been carried out on a new series of rare-earth-containing Heusler alloys having the formula Pd/sub 2/RSn (R = Tb--Yb). The Tm and Yb compounds in this series along with Lu, Sc, and Y compounds are superconducting. The magnetic susceptibility of Pd/sub 2/TmSn and Pd/sub 2/YbSn deviates from the Curie-Weiss behavior at low temperatures indicating that crystalline electric field effects are appreciable. Analysis of the magnetic susceptibility data in terms of crystalline electric fields shows that the ground state of the Tm/sup 3 +/ ion is nonmagnetic which, therefore, does not affect the superconducting state. The susceptibility of Yb/sup 3 +/ ions at low temperatures is also reduced from the free-ion value due to the crystalline electric field interaction. The Tb- and Dy-containing compounds order antiferromagnetically with Neel temperatures of 9 and 15 K, respectively, while Er- and Ho-containing compounds are paramagnetic down to 1.4 K. The hyperfine field at the Sn site in Pd/sub 2/TbSn is about 50 kOe but is only about 10 kOe in Pd/sub 2/DySn at 4.2 K.
35 citations
TL;DR: In this article, a magnetic field versus temperature (H -T ) phase diagram of GdB 6 was proposed from magnetic and transport measurements on single crystals in the temperature range from room temperature to 1.3 K and up to 550 kOe of applied magnetic field.
32 citations
TL;DR: In this article, the susceptibility of the Heisenberg model of magnetism very closely follows a power law in the high-temperature limit as well as in the limit of the Curie temperature.
Abstract: It is demonstrated that the susceptibility of the Heisenberg model of magnetism very closely follows a power law in the high-temperature limit as well as in the limit of the Curie temperature. In the high-temperature region the exponent is a function of coordination number and spin value. The discussion is limited to isotropic three-dimensional systems. The analysis should be useful for the extraction of magnetic moments from experimental data.
29 citations
TL;DR: In this article, the Curie temperature TC and θp have a broad peak at around x=0.2, and the Neel temperature decreases on increasing x, but both remain nearly constant for changing x.
Abstract: Magnetic measurements have been carried out for the new mixed crystals such as Mn1−xTixAs (and Sb) and Cr1−xCoxSb with x ranging from 0 to 1. Mn1−xTixAs is ferromagnetic if x is less than 0.7, and the magnetic moment per Mn atom is found to be nearly constant (∼3.6 μB) for changing x. The Curie temperature TC and the asymptotic Curie temperature θp have a broad peak at around x=0.2. Mn1−xTixSb is also ferromagnetic if x is less than 0.7. The magnetic moment per Mn atom estimated from the saturation magnetization at 77 K is found to be about 10% larger than that estimated from the Curie–Weiss law above TC, but both remain nearly constant for changing x. The compounds Cr1−xCoxSb are antiferromagnetic but the detail is not clear at the present stage. The magnetic susceptibility does not obey the Curie–Weiss law for each specimen. The Neel temperature decreases on increasing x.
27 citations
TL;DR: In this article, the variation with modulation wave length of the Curie temperature of a Heisenberg magnetic superlattice is studied in the molecular field approximation for the cases of square-wave and sinusoidal modulations.
TL;DR: In this article, it has been found that the susceptibility above the Curie temperature does not obey the curie-Weiss law over a very wide temperature range, and the obtained susceptibility vs temperature curves are well expressed by a formula χg=C/(T−θa)γ with a composition dependent parameter γ ranging from about 1.3 to 1.5.
Abstract: MnAlGe is a ferromagnet with a unique crystal structure including two‐dimensional arrays of Mn atoms in it. In order to find the magnetic properties characteristic of this structure, magnetic and electric measurements were made for Mn0.9M0.1AlGe (M:Mn, Cr, Fe) and MnGaGe. It has been found that the susceptibility above the Curie temperature (TC) does not obey the Curie–Weiss law over the very wide temperature range. Obtained susceptibility vs temperature curves are well expressed by a formula χg=C/(T−θa)γ with a composition dependent parameter γ ranging from about 1.3 to 1.5. In MnAlGe the formula with γ=1.49 holds in the whole temperature range from just above TC (=503 K) to Tt (=853 K, a temperature of solid‐state transition). The Curie temperature of Mn1−xMxAlGe(x≤0.2) varies monotonically when they are plotted against the averaged number of d electrons per transition‐metal atom. The temperature dependencies of saturation magnetization and electric resistivity were also measured for these specimens.
TL;DR: In this article, the initial ac susceptibility χ was examined in the temperature range from 4.2 K to Curie temperatures for polycrystalline Fe100−xNix (20≤x≤50) alloys.
Abstract: Initial ac susceptibility χ was examined in the temperature range from 4.2 K to Curie temperatures for polycrystalline Fe100−xNix (20≤x≤50) alloys. The reentrant spin glass is found in x=30–45 alloys. The dependence of the freezing temperature Tg on the intensity of driving magnetic field (ac: 0–0.26 Oe; dc: 0–10 Oe) and on the frequency (140–9200 Hz) was studied for the Fe65Ni35 alloy. A strong magnetic relaxation is observed below Tg. These results are discussed based on the cluster model.
TL;DR: The results support the view that the charge carriers of boron carbides are spinless, small, singlet bipolarons.
Abstract: We have measured the magnetic susceptibility of several boron carbides, including B/sub 4/C, B/sub 15/C/sub 2/, and B/sub 9/C, over the temperature range 2--400 K with magnetic fields between 1 and 50 kOe. In general, the susceptibility follows a Curie law with a temperature-independent diamagnetic contribution. There is some ferromagnetic contribution to the susceptibility. However, the density of ferromagnetic impurities is considerably less in our samples than in commercial samples. The paramagnetic spin concentration is compared with the carrier concentration determined by transport measurements (conductivity, Hall effect, and Seebeck effect) on the same samples. The spin concentration is about 2 orders of magnitude smaller than the carrier concentration. We attribute the observed spins to defects and impurities. Thus, our results support the view that the charge carriers are spinless, small, singlet bipolarons.
TL;DR: In this paper, the magnetic susceptibility of both these compounds may be described as the sum of a Curie-Weiss term dominating at low temperature and a large temperature independent term, and the heat capacity measurements yield the value of electronic specific heat coefficient γ of 40.1 and 15.6 mJ/mol K2 for Os and Ru compounds, respectively.
TL;DR: In this paper, the entropy and magnetization curves for solid3He as obtained from multiple exchange mean field calculations are presented as a function of temperature and magnetic field, and compared with experiments.
Abstract: Entropy and magnetization curves for solid3He as obtained from multiple exchange mean field calculations are presented as a function of temperature and magnetic field, and compared with experiments. Melting curves in high magnetic fields and end temperatures after adiabatic decompression of magnetic solid3He are also derived.
TL;DR: In this paper, a set of all limit (Gibbs) states for the ferromagneticn-vector Curie-Weiss model is constructed by means of a generalized quasiaverage method.
Abstract: A set of all limit (Gibbs) states is constructed for the ferromagneticn-vector Curie-Weiss model by means of a generalized quasiaverage method.
TL;DR: The magnetic susceptibility of Dy(Fe1−xAlx)2 compounds with 0.1 < x < 0.8 showed a strong field dependence over a wide temperature range above the Curie temperature.
Abstract: The magnetic susceptibility of Dy(Fe1−xAlx)2 compounds with 0.1 < x < 0.8 showed a strong field dependence over a wide temperature range above the Curie temperature. Electron spin resonance (ESR) investigations in the X band showed anomalous temperature variations in the ESR parameters (i.e. linewidth, resonance field and relative intensity) and marked time and temperature hysteresis. The results of structural, magnetic and ESR investigations indicated the existence of short-range magnetic order of the iron atoms (magnetic iron clusters) above the Curie temperature.
TL;DR: In this article, the magnetic properties of the ordered phase in the Ni 3 Al 1− x Mn x solid solution with x = 0, 0.4 K and the Curie temperature increase monotonically with increasing Mn concentration up to 15 at%.
TL;DR: The magnetic susceptibility of /sup 3/He adsorbed on sintered silver powder has been measured in the temperature range from 0.8 mK to about 10 with a SQUID magnetometer for eight different film thicknesses between monolayer and 15 layers.
Abstract: The magnetic susceptibility of /sup 3/He adsorbed on sintered silver powder has been measured in the temperature range from 0.8 mK to about 10 with a SQUID magnetometer for eight different film thicknesses between monolayer and 15 layers. The measured susceptibility of films less than about 5 layers thick obeys the Curie law with the Curie constants given by the free localized model. In films more than 5 layers thick, the measured susceptibility is described by the Curie-Weiss behavior with Curie-Weiss temperature of about 0.4 mK.
TL;DR: Amorphous ferromagnets exhibit an unusually large temperature range of deviations from the Curie-Weiss behavior in the paramagnetic regime and the question is discussed whether this may be interpreted as an extended critical behavior or as a non-critical phenomenon for which scaling ideas are not valid as discussed by the authors.
TL;DR: The thermodynamic Bethe-ansatz equations of the Coqblin-Schrieffer model for j = 5 2 are solved numerically in the presence of a magnetic field as discussed by the authors.
TL;DR: In this article, the Bethe-Neel dependence and a prediction of the magnetic Gruneisen parameter using an itinerant-electron theory of ferromagnets are discussed.
Abstract: The Curie temperature of the Dy2Fe17-yAly series has been measured by means of AC susceptibility. The Al concentration dependence of Tc initially (up to y=3) increases although the magnetic iron atoms are gradually diluted. The present study shows that this effect is not connected with a crystal structure but is due to an increase of the average iron-iron distance caused by Al substitution. The author has shown that the Curie temperature of all heavy-rare-earth-iron compounds of the 2:17 type increases smoothly with increasing volume. A value of 6000K has been evaluated for dTc/d ln V, resulting in a value of -17 for the magnetic Gruneisen parameter Gamma m=-d ln Tc/d ln V. As the Curie temperature in these compounds is governed mainly by the iron-iron exchange interaction they have inferred a strong dependence of the JFe-Fe coupling on the 3d-3d distance. The Bethe-Neel dependence and a prediction of the magnetic Gruneisen parameter using an itinerant-electron theory of ferromagnets are discussed.
TL;DR: In this paper, magnetic susceptibility measurements have been made on samples of californium-249 metal having the dhcp crystal structure at temperatures between 100 and 340 K and at fields up to 50 kilogauss, the samples exhibit Curie-Weiss behavior.
Abstract: Magnetic susceptibility measurements have been made on samples of californium-249 metal having the dhcp crystal structure. At temperatures between 100 and 340 K and at fields up to 50 kilogauss, the samples exhibit Curie-Weiss behavior. Previous measurements extending only to 1.6 kilogauss gave a magnetic moment per atom of μeff = (10.7±0.2)μB and paramagnetic Weiss temperatures. Θp, in the range of −2 to −16 K for two samples. These values of μeff are in good agreement with the value expected (10.62μB) for a free-ion 5f9 configuration based on an L-S coupling scheme and Hund's rule. In this work extended to higher fields, two additional samples give the values μeff = (9.7 ± 0.2)μB and Θp = −40 K. At low temperatures the samples exhibit an ordered magnetic transition to a state with a saturated moment of 6.1μB/atom when extrapolated to infinitely high field. The low temperature ordered phase exists at temperatures below Tc = (51 ± 2) K as determined from constant magnetization plots.
TL;DR: In this paper, the effect of pressure on the magnetisation of UFe2 at 4.2K and the effect on the Curie temperature are compared with interpreted as indications for itinerant ferromagnetism.
Abstract: The effect of pressure on the magnetisation of UFe2 at 4.2K and the effect of pressure on the Curie temperature are compared with interpreted as indications for itinerant ferromagnetism. Moreover, these pressure effects, studied in the series U(FexCo1-x)2 show a behaviour that is in qualitative agreement with this model. Magnetisation curves around the Curie temperature are analysed in terms of critical behaviour. The pressure dependence of the parameters so derived is obtained and related to the temperature and pressure dependence of the intrinsic moment. From this analysis it is deduced that, contrary to what is expected in Stoner-Edwards-Wohlfarth theory, the magnetic moments do not completely disappear above the Curie temperature.
TL;DR: In this article, a modified equation of state is proposed, which allows the use of the Arrott plots at high magnetic fields, which is shown to fit rather well the experimental data of Potter on crystalline Fe, and those of Kaul and Rosenberg on amorphous Fe13Ni67B19Si alloy.
Abstract: A modified equation of state is proposed, which allows the use of the Arrott plots at high magnetic fields. The equation is shown to fit rather well the experimental data of Potter on crystalline Fe, and those of Kaul and Rosenberg on amorphous Fe13Ni67B19Si alloy.
TL;DR: In this article, the Curie-Weiss Law is generalized to take into account differences among lattices, spin values, and range of exchange interactions, and several forms of the generalization are given for the purpose of facilitating the abstraction of magnetic moments from susceptibility data.
Abstract: The Curie–Weiss Law is generalized to take into account differences among lattices, spin values, and range of exchange interactions. Several forms of the generalization are given for the purpose of facilitating the abstraction of magnetic moments from susceptibility data. A parameter γp is introduced that describes exactly the behavior in the high temperature limit and correlates well with the behavior nearer to the critical temperature.
TL;DR: In this paper, the magnetic susceptibilities of SnMo6S8, PbMo6.35S8 and PbM6.2S8 have been measured and the behavior of the susceptibility is believed to be caused by changes in the lattice.
Abstract: The magnetic susceptibilities of SnMo6S8, PbMo6.35S8, and PbMo6.2S8 have been measured. There appear to be transitions at about 40 and 100 K. The behavior of the susceptibility is believed to be caused by changes in the lattice, affecting the charge transfer from the tin or lead atoms to the Mo6S8 clusters.
TL;DR: In this paper, Fe2N has been identified as a new weak itinerant ferromagnet by magnetic measurements and the magnetic properties were analyzed according to the Stoner-Edwards-Whlfarth (SEW) model, which gives results in agreement with the magnetization and susceptibility measured at temperatures below Tc.
Abstract: ξFe2N has been identified as a new weak itinerant ferromagnet by magnetic measurements. It has the highest ratio qc/qs of effective atomic moment qc to the atomic moment qs, and a low Curie temperature Tc=7K. The magnetic properties were analysed according to the Stoner-Edwards-Whlfarth (SEW) model, which gives results in agreement with the magnetization and susceptibility measured at temperatures below Tc.