Showing papers on "Curie–Weiss law published in 1994"
TL;DR: In this paper, the magnetic moment and susceptibility of diamond, graphite along and perpendicular to the c axis, and carbon nanotubes are reported as a function of magnetic field (0H55 kOe) and temperature (4.5 KT310 K).
Abstract: Measurements of the magnetic moment and susceptibility of diamond, graphite along and perpendicular to the c axis, ${\mathrm{C}}_{60}$, and carbon nanotubes are reported as a function of magnetic field (0H55 kOe) and temperature (4.5 KT310 K). The data on ${\mathrm{C}}_{60}$ are diamagnetic, confirm previous results, and show the influence of the phase transition near 260 K. The data on the nanotubes were taken on a sample containing a distribution of tubes with diameters in the 2--10 nm range, and reveal a mostly diamagnetic behavior with a magnetic field and temperature dependence different from graphite.
149 citations
TL;DR: In this paper, the authors discuss two methods that quantify the contribution of different groups to the AMS: (1) comparative measurements of the magnetic susceptibility in low fields and high fields and (2) heating curves from 77 K to room temperature (low temperature magnetic susceptibility, LTMS).
148 citations
TL;DR: In this paper, the magnetic properties of high anisotropy Sm(Co1−xCux)5 phases were determined experimentally at 300 K in the range x < 0.6.
Abstract: The magnetic characteristics of high‐anisotropy Sm(Co1−xCux)5 phases are determined experimentally at 300 K in the range x<0.6. The saturation magnetization Ms decreases and vanishes for SmCo2Cu3. Identical behaviors of Ms and Curie temperature TC versus x are observed in the range x<0.6. For significant Cu substitution rate (x≳0.35), the decrease of the anisotropy field (HA) when x increases is strong. For lower Cu contents, huge values of anisotropy fields make difficult the accurate determination of the substitution effect. The first anisotropy constant K1 is calculated using the available values of HA and Ms. A linear decrease of K1 is observed from SmCo5 to SmCo2Cu3.
141 citations
TL;DR: In this paper, an N-layer film of simple cubic symmetry with nearest-neighbour exchange in which the exchange strength and transverse field are assumed to be different from the bulk values in Ns surface layers, and derive and illustrate expressions for the phase diagrams, order parameter profiles, specific heat and susceptibility.
Abstract: Ferroelectric films described by an Ising model in a transverse field have been studied under the mean-field approximation. We discuss an N-layer film of simple cubic symmetry with nearest-neighbour exchange in which the exchange strength and transverse field are assumed to be different from the bulk values in Ns surface layers, and we derive and illustrate expressions for the phase diagrams, order parameter profiles, specific heat and susceptibility. In such films, the Curie temperature can shift to either lower and higher temperature compared with the corresponding bulk value. If the surface exchange strength is strong enough, there is still a phase transition to ferroelectricity even when the transverse field is larger than the bulk critical value. In surface-enhanced films with Ns>or=2 the maximum in the order parameter profile occurs in the layers next to the outermost surface layer. The bulk peak of the specific heat becomes a discontinuity at the film Curie temperature. There is a rounded peak at the bulk Curie temperature if the surface exchange strength is higher than the critical value. The dim susceptibility still diverges at the film Curie temperature, as does the bulk susceptibility, but its magnitude is reduced. Also there is a rounded peak at the bulk Curie temperature when the surface exchange strength exceeds the critical value. The bulk-related character of the specific heat and susceptibility is less pronounced and the surface-related character is more pronounced when the film thickness is small or the surface-layer number is large.
68 citations
TL;DR: In this paper, the sign of magnetic interaction is discussed in connection with the orthorhombic lattice distortion, and the antiferromagnetic interaction is attributed to this distortion.
Abstract: Electrical resistivity ρ and magnetic susceptibility of sintered Ca 1- x Sr x RuO 3 have been measured. The Weiss temperature changes sign at about x =0.5 in consistent with other studies. Temperature dependence of normalized ρ is almost identical for all the materials in the paramagnetic temperature range irrespective of the sign of magnetic interaction. The Rhodes-Wolfarth ratio is 1.3 for x =1. This ratio and the temperature dependence of ρ suggest that 4 d -electrons in this system are in the intermediately localized state as in Ni. The sign of magnetic interaction is discussed in connection with the orthorhombic lattice distortion, and the antiferromagnetic interaction is attributed to this distortion.
66 citations
TL;DR: The magnetic susceptibility data for 1-3 in the temperature range 5-300 K obey the Curie Weiss law (χM−1 = (T − θ)/C) with a positive Weiss constant (+18 K for 1, +24 K for 2, and +41 K for 3).
Abstract: The reaction of potassium calcium tris(dithiooxalato)chromate(III) hexahydrate KCa[Cr(dto)3]·6H2O, a metal(II) salt and a tetrapropylammonium bromide (NPr4Br) in aqueous methanol forms bimetallic assemblies {NPr4[MCr(dto)3]}x (M = Fe (1), Co (2), Ni (3), Zn (4)), where the dto group bridges Cr(III) and M(II) ions through the sulfur atoms to Cr(III) and through the oxygen atoms to M(II) to provide an alternate array of Cr(III) and M(II) ions. The magnetic susceptibility data for 1—3 in the temperature range 5—300 K obey the Curie Weiss law (χM−1 = (T − θ)/C) with a positive Weiss constant (+18 K for 1, +24 K for 2, and +41 K for 3), and the effective magnetic moments increase with decreasing temperature. The megnetization studies (field-cooled magnetization, remnant magnetization, and zero-field cooled magnetization) reveal the ferromagnetic phase transition at TC = 8, 16, and 23 K for 1, 2, and 3, respectively. The assembly 4 shows paramagnetic behavior in the temperature range of 5—300 K.
66 citations
TL;DR: In this paper, the structural and magnetic properties of two compounds from the Me32+Fe3+CN6+23−H2O family were analyzed in the framework of the mean-field theory.
Abstract: We have studied the structural and magnetic properties of two compounds from the Me32+(Fe3+(CN)6-)23-.H2O family, where Me=Ni and Co. From x-ray analysis we find that the compounds crystallize in the face-centred cubic structure with the space group of F43m. Both the Fe and Me ions are coordinated octahedrally by six carbon atoms and six nitrogen atoms, respectively. The Fe ions are in a strong crystalline field, while the Me ions are in an intermediate field with cubic symmetry. From the magnetic studies a quantitative bulk ferromagnetic behaviour (a spontaneous magnetization and a hysteresis loop) has been established for both complex compounds. In addition, from the magnetization against temperature curves we obtained, for both compounds, the Curie as well as Curie-Weiss temperatures, the Curie constants and the effective moments in the paramagnetic state. From the assumed value of the spin for every cation we fitted the chi T=F(T) curves and from the field dependence of the magnetization we determined the high-field susceptibility. The magnetic properties of the compounds were analysed in the framework of the mean-field theory.
56 citations
TL;DR: The magnetic susceptibility and microwave properties of powder samples of 1,3,5-triphenyl-6-oxoverdazyl were investigated between room temperature and 18 K as mentioned in this paper.
49 citations
TL;DR: In this paper, the authors studied the Curie temperature of a ferroelectric superlattice formed from two alterating materials using the transverse Ising model in the mean-field theory.
43 citations
TL;DR: The temperature dependence of magnetic susceptibility has been measured in a temperature region from about 100 to 500 K for the compounds RCo3B2 with R=Y, Sm, Gd, and Dy.
Abstract: The temperature dependence of magnetic susceptibility has been measured in a temperature region from about 100 to 500 K for the compounds RCo3B2 with R=Y, Sm, Gd, and Dy. Their magnetization curves at T=5 K have also been measured in a pulsed high field up to 170 kOe. YCo3B2 seems to have a Pauli paramagnetic nature down to T=5 K. In the paramagnetic temperature region, SmCo3B2 exhibits Van Vleck paramagnetism; however, GdCo3B2 and DyCo3B2 show Curie–Weiss character. The paramagnetic susceptibility for all compounds mentioned above is found to include a Pauli paramagnetic contribution from the Co sublattice. In the case of GdCo3B2 at T=5 K, the magnetic moment of 0.2μB/Co, which is antiparallel to the Gd moment, is considered to be induced by the exchange field from the Gd spin. A similar induced moment of 0.14μB/Co is also estimated in DyCo3B2. The Sm‐ and Dy‐sublattice moments at T=5 K are smaller than the free‐ion values, which can be explained by the crystal‐field theory. A relatively large value of B...
38 citations
TL;DR: In this article, a discrepancy between experimental and theoretical values of the magnetic moment, which increases with increasing Zn content, was observed, due to the partial occupation of the octahedral sites by the Zn2+ ions and resulting in random spin canting.
Abstract: Polycrystalline samples of Ba2(ZnxFe1−x)2Fe28O46 [(ZnxFe1−x)2−X, 0≤×≤1] X‐type hexaferrites were prepared by the ceramic method. Magnetization, magnetic moment, and Curie temperature were investigated. With increasing Zn content the magnetization and magnetic moment increase linearly, but the Curie temperature decreases. A discrepancy between experimental and theoretical values of the magnetic moment, which increases with increasing Zn content, was observed. The effect may be due to the partial occupation of the octahedral sites by the Zn2+ ions and resulting in random spin canting.
TL;DR: In this paper, a new compound, CaAl4Fe8O19, was synthesized for the first time and characterized by X-ray diffraction, which was found to have a hexagonal magnetoplumbite structure with lattice parametersa=5·83 A andc=22·14 A. The electrical studies showed that the compound was a semiconductor with energy of activationq=0·86 eV.
Abstract: A new compound, CaAl4Fe8O19, was synthesized for the first time and characterized by X-ray diffraction. It was found to have a hexagonal magnetoplumbite structure with lattice parametersa=5·83 A andc=22·14 A. The electrical studies showed that the compound was a semiconductor with energy of activationq=0·86 eV. The magnetic susceptibility was studied in the temperature range 300 K to 850 K, in which the compound was paramagnetic with a Curie molar constant of 31·03.
TL;DR: In this paper, the temperature, frequency, and field dependence of the magnetic properties of small clusters of up to 28 Fe0 atoms in NaY zeolite has been measured.
Abstract: Clusters of up to 28 Fe0 atoms have been introduced into the ‘‘supercages’’ of NaY zeolite by ion exchange of Fe+2 for Na+ followed by reduction to Fe0 with solvated electrons and Na−1 ions. The temperature‐dependent ac and dc susceptibilities, which exhibit Curie–Weiss behavior before reduction, change to something approximating superparamagnetic behavior afterwards. The blocking temperature, Tb shows a strong dependence on magnetic field but weak dependence on frequency. There is at best a very weak remanence and coercive field while the onset of irreversibility occurs at temperatures well above Tb. In addition, the real and imaginary parts of the ac susceptibility show essentially similar temperature dependence. Some of this anomalous behavior can be attributed to a distribution of particle sizes. To the best of our knowledge these preliminary data—while poorly understood—represent the first measurements of the temperature, frequency, and field dependence of the magnetic properties of such small clusters.
TL;DR: In this article, the magnetic field dependence was fitted to a modified Brillouin function in order to determine the effective spin states of the paramagnetic species, under the assumption of complete quenching of the orbital momentum.
Abstract: The magnetization and static magnetic susceptibility of fusinite and synthetic carbohydrate chars are reported for magnetic fields up to 5.5 T and temperature range 2-320 K. The low-field magnetic susceptibility data exhibited Curie-Weiss behavior over the whole temperature range. The Weiss constant characterizes the overall exchange as antiferromagnetic, of the order of 1 K for all samples studied. The magnetic field dependence was fitted to a modified Brillouin function in order to determine the effective spin states of the paramagnetic species. Under the assumption of complete quenching of the orbital momentum, the spin quantum number was derived from the characteristic shape of the Brillouin function as well as from the ratio of the Curie constant to the saturation magnetization
TL;DR: In this article, the Curie-Weiss behavior of the susceptibility above 80 K yields values of /spl Thetasub p/ equal to -98, 3 and 41 K for the a, b and c axis, respectively.
Abstract: Magnetism in UNiGe which adopts the orthorhombic TiNiSi type of structure with lattice constants a=700.7 pm, b =423.7 pm, c=720.7 pm is strongly anisotropic. The Curie-Weiss behaviour of the susceptibility above 80 K yields values of /spl Thetasub p/ equal to -98, 3 and 41 K for the a, b and c axis, respectively. Also the electrical resistivity is anisotropic and reflects magnetic phase transitions at 41.5 and 50 K, in very good agreement with specific-heat data. An antiferromagnetic structure of U moments of about 1.4 /spl musub B/ with a propagation vector q=(0, 0.5, 0.5) can be concluded from neutron-diffraction studies at low temperatures. Two metamagnetic transitions are observed in high-field magnetization data at 4.2 K in fields applied along the b (at 17 and 25 T) and c (at 3 and 10 T) axes yielding parallel alignment of the magnetic moments in fields above the second transition. The magnetization measured at 35 T amounts to 1.45 /spl musub Bf.u. The huge magnetic anisotropy is reflected in the weak linear magnetic response to fields along the a axis yielding only 0.23 /spl musub Bf.u. at 35 T. The destruction of antiferromagnetic ordering in high fields is accompanied by a reduction of about 80 of the electrical resistivity. The huge magnetic anisotropy and giant magnetoresistance which is also observed in other UTX compounds (T=transition metal, X=p-metal) can be understood in terms of anisotropic 5f-ligand hybridization. >
TL;DR: The magnetization of a stable single-grained Al 70 Pd 21 Mn 9 icosahedral quasicrystal has been investigated in the temperature region between 2 and 600 K below the magnetic field 80 kOe as mentioned in this paper.
Abstract: The magnetization of a stable single-grained Al 70 Pd 21 Mn 9 icosahedral quasicrystal has been investigated in the temperature region between 2 and 600 K below the magnetic field 80 kOe. The susceptibility yields a Curie constant 1.75×10 -4 cgsemu·K/g, a Curie temperature -1.62 K, and a constant susceptibility contribution -0.25×10 -8 cgsemu/g. Magnetization curves at low temperatures suggest that only about 1% of the Mn atoms are magnetic. The temperature dependence of the susceptibility above 300 K shows a positive T 2 contribution, which has been first observed in magnetic quasicrystals and is considered to originate from a pseudogap in the electronic density of states at E F causing the stability. Temperature- and magnetic-field-dependencies of the electrical conductivity are well accounted for by a weak localization theory including spin and spin-orbit scattering. The agreement between the experimental data and the fitting is not improved by adding the diffusion channel contribution of electron-elec...
TL;DR: In this article, the formation of two new materials, Sm2Ni3Si5 and Gd2Ni 3Si5, of the rare earth series R2M3 Si5 (R denotes rare earth and Y) and their magnetic and transport properties are reported.
Abstract: The formation of two new materials, Sm2Ni3Si5 and Gd2Ni3Si5, of the rare‐earth series R2M3Si5 (R denotes rare earth and Y) and their magnetic and transport properties are reported here. These materials crystallize in the orthorhombic U2Co3Si5‐type structure (space group Ibam). The magnetic susceptibility of Gd2Ni3Si5 follows a Curie–Weiss behavior with an effective magnetic moment 8.1μB/Gd ion. The material orders antiferromagnetically at ≊15 K. The magnetic susceptibility of Sm2Ni3Si5 exhibits a deviation from the Curie–Weiss behavior which is attributed to the low‐lying excited state of Sm3+ ions and also to crystal‐field effects. This material also orders antiferromagnetically, but at ≊11 K. This value of the ordering temperature does not seem to follow the de Gennes scaling with respect to that of Gd2Ni3Si5.
TL;DR: The structure and magnetic properties of FeAl1−xRhx alloys have been studied by X-ray, magnetization and Mossbauer effect measurements as discussed by the authors, and the crystal structure of these alloys remains in B2 type.
TL;DR: In this article, the distribution of the q-mode magnetization fluctuations as a function of the temperature, the wave vectorq, and a fading out external field was computed. And new classes of probability distributions generated by this external field as well as new critical behavior in terms of its rate of fading out.
Abstract: It is known that at the critical temperature the Curie-Weiss mean-field model has non-Gaussian fluctuations and that “internal fluctuations” can be Gaussian. Here we compute the distribution of theq-mode magnetization fluctuations as a function of the temperature, the wave vectorq, and a fading out external field. We obtain new classes of probability distributions generated by this external field as well as new critical behavior in terms of its rate of fading out. We discuss also the susceptibility as the limitq tending to zero.
TL;DR: In this article, it was shown that zero-field muon spin relaxation studies of the critical paramagnetic fluctuations in ferromagnets are mostly sensitive to fluctuation modes at small wave vectors.
Abstract: We show that zero-field muon-spin-relaxation studies of the critical paramagnetic fluctuations in ferromagnets are mostly sensitive to fluctuation modes at small wave vectors. The transverse-fluctuation modes can be probed very close to the zone center when the temperature approaches the Curie temperature. A quantitative determination of the zone probed in Ni and Fe is performed.
TL;DR: In this article, the Curie temperatures of magnetic 3D elements and yttrium intermetallics are investigated using densities of states obtained by self-consistent LMTO band-structure calculations.
Abstract: The Curie temperatures of magnetic 3d elements and yttrium intermetallics are investigated. Using densities of states obtained by self-consistent LMTO band-structure calculations, it is shown that the Curie temperatures in strong and nearly strong ferromagnets cannot be understood in terms of extensions of the theory of very weak itinerant ferromagnetism such as the Mohn-Wohlfarth approach. In particular, a knowledge of the partial densities of states D up arrow (EF) and D down arrow (EF) around the Fermi level is not sufficient to deduce the Curie temperature. Reasons for this are the non-analytic character of the density of states and k-space delocalization of the thermal excitations.
TL;DR: The magnetic structures in UNiGe confirm that the strong bonding of 5f orbitals along the a axis leads to a huge magnetic anisotropy with U magnetic moments perpendicular to this direction as discussed by the authors.
TL;DR: Based on former theories, a formula for estimating the Curie temperature of binary, ferromagnetic Ising systems on the simple-cubic lattice is proposed and in good agreement with the known mean-field-like approaches.
Abstract: The concentration dependence of the Curie temperature in binary, ferromagnetic Ising systems on the simple-cubic lattice is studied by high-accuracy Monte Carlo simulations using the Swendsen and Wang algorithm. Our results are in good agreement with the known mean-field-like approaches. Based on former theories, a formula for estimating the Curie temperature of these systems is proposed.
TL;DR: In this paper, the temperature dependence of the magnetization for amorphous Gd 65 Co 35 below 340 K in magnetic fields up to 5.27 T was investigated and it was shown that T 2.00±0.05 is the functional form of another dominant contribution to the temperature of magnetization than the spin wave term T 3/2.
Abstract: We present detailed investigation of the temperature dependence of the magnetization for amorphous Gd 65 Co 35 below 340 K in magnetic fields up to 5.27 T. The paramagnetic susceptibility follows the Curie-Weiss law. We experimentally find that T 2.00±0.05 is the functional form of another dominant contribution to the temperature dependence of the magnetization than the spin wave term T 3/2 . These T 2 and T 3/2 terms are interpreted as longitudinal and transverse fluctuations in the local moment derived from polarization of the spin bands. The longitudinal fluctuation comes from itinerant character of 3 d electrons in Co atoms.
TL;DR: Magnetic susceptibility of YMn/sub x/Al/sub 12-x/ (x=4,5,6) with ThMn-sub 12/ structure was measured at temperatures 90 K to 900 K.
Abstract: Magnetic susceptibility of YMn/sub x/Al/sub 12-x/ (x=4,5,6) with ThMn/sub 12/ structure was measured at temperatures 90 K to 900 K. These compounds show varied magnetic behaviors depending upon the relative abundance of Mn atoms in the 8f, 8j and 8i crystallographic sites. In the high temperature range, the temperature dependence of the susceptibility is of the Curie-Weiss type. The occurrence of a Mn moment in YMn/sub 4/Al/sub 8/ and YMn/sub 6/Al/sub 6/, is strongly correlated with the critical value d/spl ap/2.6 /spl Aring/ of Mn-Mn distance below which the Mn moment collapses, In YMn/sub 6/Al/sub 6/, both the magnetic and the nonmagnetic Mn atoms were observed to coexist. It has been revealed that the magnetic character of Mn moment in the 8f sites of these two compounds changes from an itinerant electron type to a local moment type with increasing temperature. A transition to a spin glass state at ion temperatures for YMn/sub 5/Al/sub 7/ was suggested,. >
TL;DR: In this article, KUO[sub 3] (cubic perovskite structure) was prepared and its magnetic susceptibility was measured from 4.2 K to room temperature, and it was found that a magnetic anomaly (magnetic transition) occurred at 16.8 K and that this transition temperature decreased with increasing magnetic field.
TL;DR: In this article, the magnetic properties of a diluted spin-3 2 Ising ferromagnet on a honeycomb lattice are examined by the use of the new formulation based on both the Ising spin identities and the differential operator technique.
TL;DR: In this paper, the structural and magnetic properties of the Me 2 [Fe(CN) 6 ] family were studied at room temperature and the magnetic studies in the temperature range 4.2-260 K using static magnetic fields up to 12 T. The results indicated that only the divalent Me cations are magnetic and coupled ferromagneticically between each other.
TL;DR: In this article, the authors measured the magnetization of magnetic liquids containing amorphous iron-carbon particles with diameters 3.2, 3.8 and 5.0 nm in fields from 2 to 12 T and at temperatures from 50 to 290 K.