Curie-Weiss Term Research Articles

Low-temperature study of the susceptibility in the anisotropic spin glass Fe2TiO5

The authors study the susceptibility of the anisotropic spin glass Fe2TiO5 below 1K. An unusual contribution to the magnetic susceptibility is revealed by an increase in the susceptibility as temperature is decreased. This increase is attributed to 'loose' spins which, due to the frustration in this system, experience zero internal field and contribute a Curie-Weiss term to the susceptibility. This contribution is anisotropic in nature.

Superconductivity in the ternary borides CeOs 3B 2 and CeRu 3B 2: Magnetic susceptibility and specific heat measurements

The compounds CeOs 3B 2 and CeRu 3B 2 show superconductivity with T c's of 3.5 and 1.1 K respectively. 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. The heat capacity measurements yield the value of electronic specific heat coefficient γ of 40.1 and 15.6 mJ/mol K 2 for Os and Ru compounds, respectively. These compounds appear to be conventional bulk superconductors in which Ce is in a strongly mixed valent state.

EPR and magnetic susceptibility of Gd 2Co 6Al 11 intermetallic compound

The EPR of Gd 3+ ions and the magnetic susceptibility of Gd 2Al 17 and Gd 2Co 6Al 11 are reported. The contributions to the magnetic susceptibility are the Curie-Weiss term, expressing the paramagnetism of the localized f and d electrons of Gd and Co atoms, and a temperature-independent term for which all the contributions have been estimated. From the experimental Δ g shifts the magnetic susceptibility data were estimated the exchange integrals J sf=−0.03 eV and J sd=−0.01 eV between the conduction electrons and the localized f and d electrons, respectively.

Crystallographic and Magnetic Studies on TixV3-xS4System

Polycrystalline samples of Ti x V 3- x S 4 were prepared in 0 ≦ x ≦3. For x ≦2.0 metal vacancies are in an ordered arrangement and for x ≧2.5 they are disordered. Magnetic susceptibility χ follows the equation χ=χ 0 + C /( T -θ). The Curie constant increases linearly with x for x ≦2.0 and corresronds to the magnetic moment of ∼0.7 µ B /Ti. C is very small for x ≧2.5. Discussions are made about the Curie-Weiss term in conjunction with the structural phase transition.

Ferromagnetism in TiMn ternary hydrides

The magnetic behaviour of TiMn intermetallics and their hydrides was investigated by susceptibility measurements in the temperature range 5–360 K and magnetization measurements in the temperature range 4–250 K with fields up to 7.2 T. The three TiMn intermetallics that are stable at low temperature (the C14 Laves phase with a wide range of homogeneity from Ti 0.33Mn 0.67 to Ti 0.45Mn 0.55, the ρ phase Ti 0.46Mn 0.54 and the φ phase Ti 0.48Mn 0.52) are paramagnetic with susceptibilities that are independent of temperature. The Laves-phase hydride retains the C14 structure with a lattice volume expansion of 27%. All three hydrides are ferromagnetic with Curie temperatures T c of about 212, 87 and 155 K respectively that are slightly dependent on the hydrogen content. The susceptibilities above T c consist of Curie-Weiss terms and very large temperature-independent terms. The onset of ferromagnetism in these TiMn ternary hydrides is due to the volume expansion and/or to the increase in the density of states at the Fermi level on hydrogenation.

Magnetic and electronic properties of CoTi1-xAlxcompounds

The susceptibility of paramagnetic Al-rich and Ti-rich CoTi1-xAlx compounds consists of two contributions; a matrix susceptibility that becomes strongly enhanced at the Ti-rich side and a Curie-Weiss term that is ascribed to structural defects. High magnetic field (up to 350 kOe) and high pressure (up to 5 kbar) experiments point to a band-type description of the magnetic properties of the ferromagnetic and paramagnetic Ti-rich compounds. The electronic contribution to the specific heat increases as one goes from CoAl to CoTi with a local minimum for the Heusler compound CoTi0.5Al0.5.

Magnetic susceptibilities and knight shifts of the intermetallic compounds NdCu 4 and NdCu 5

The magnetic susceptibility and Knight shift of the intermetallic compounds NdCu 4 and NdCu 5 were investigated over the temperature range 80–850 K. The most important contributions to the magnetic susceptibility are the Curie-Weiss term, expressing the paramagnetism of the localized 4ƒ-electrons, and a temperature independent term, both of which have been determined. The phenomenological quantity J sƒ between the 4ƒ-electron and conduction electron spins was found to be −2.46.10 −3eV for NdCu 4 and 1.35.10 −3 eV for NdCu 5. A reversal in the sign of the s-ƒ coupling for CeCu 5 was noted.

Coexistence of superconductivity and antiferromagnetic order in SmRh 4B 4

The ternary rare earth compound SmRh 4B 4 has been studied by means of upper critical field, low temperature specific heat, and static magnetic susceptibility measurements. A lambda-type specific heat anomaly, a discontinuity in the slope of the upper critical field versus temperature curve, and a cusp-like feature in the magnetic susceptibility suggest that superconductivity and long-range antiferromagnetic order coexist in SmRh 4B 4 below 0.87 K. Machida's theory for antiferromagnetic superconductors provides a good description of the upper critical field data, while the magnetic susceptibility data can be represented as the sum of a Curie-Weiss term with micro eff = 0.632 micro B and θ p = −1.93 K and a temperature independent Van Vleck contribution.

Static and dynamic properties of localized Mn moments in liquid bismuth

We present measurements of static susceptibility and of $^{55}\mathrm{Mn}$ and $^{209}\mathrm{Bi}$ NMR shifts and relaxation times over temperatures ranging from 700 - 1400 K for a series of dilute alloys of Mn in liquid Bi. The Mn impurities, which possess a local moment similar to that of $\mathrm{Cu}\mathrm{Mn}$, are found to exhibit a Kondo temperature ${T}_{K}\ensuremath{\sim}50$ K. A plot of $^{55}\mathrm{Mn}$ shift versus measured impurity susceptibility reveals a small temperature-independent susceptibility term in addition to the Curie-Weiss term. The fluctuation rate of the Mn moment is deduced from relaxation measurements of the $^{55}\mathrm{Mn}$ nuclei, yielding a single-ion term in good agreement with the dynamic susceptibility model for Kondo systems given by G\"otze and Schlottmann, and a spin-spin Ruderman-Kittel-Kasuya-Yosida (RKKY) term in reasonable accord with realistic model calculations for nearfield RKKY exchange. Failure of the $^{209}\mathrm{Bi}$ shift to follow the Mn susceptibility is attributed to temperature-dependent transferred hyperfine coupling; a successful interpretation of this effect is made using x-ray and neutron-diffraction results to determine the temperature-dependent radial distribution function and employing a simple asymptotic model of the RKKY spin-density oscillations. The RKKY amplitude so determined is found to be anomalously large, while the phase (at near-neighbor distances) is in agreement with a recent model calculation for $\mathrm{Cu}\mathrm{Mn}$. By applying a small correction to the moment fluctuation times from liquid motion, we are also able to obtain a quantitative interpretation of the $^{209}\mathrm{Bi}$ relaxation times.

AB INITIO calculations of the electronic properties of [formula omitted

The magnetic susceptibility and Knight shift of the intermetallic compounds NdCu4 and NdCu5 were investigated over the temperature range 80–850 K. The most important contributions to the magnetic susceptibility are the Curie-Weiss term, expressing the paramagnetism of the localized 4ƒ-electrons, and a temperature independent term, both of which have been determined. The phenomenological quantity Jsƒ between the 4ƒ-electron and conduction electron spins was found to be −2.46.10−3eV for NdCu4 and 1.35.10−3 eV for NdCu5. A reversal in the sign of the s-ƒ coupling for CeCu5 was noted.

Structure cristalline et proprietes physiques de Cu 0.65VS 2

A second form of compounds Cu xVS 2 is described here. As in Cu 0.75VS 2 (1) the structure of Cu 0.65VS 2 is related to the CdI 2-type. In Cu 0.75VS 2, Cu atoms are ordered in tetrahedral sites between the CdI 2-type subunits, whereas in the Cu 0.65VS 2, Cu atoms are partially disordered and occupy 4 different sites. Both structures differ from one another in vanadium atoms arrangements: In Cu 0.75VS 2, V-atoms form triangular clusters while in Cu 0.65VS 2 they form zigzag chains perpendicular to the hexagonal axis. The physical properties show a metallic type behaviour. Resistivity decreases with temperature with low 300 K/4.2 K ratio according to a disordered nature of the compound. Magnetic susceptibility shows a Pauli paramagnetism with an additionnal Curie-Weiss term due to a relatively large amount of paramagnetic impureties (0,9 % V 3+ atoms). The observed low temperature localisation of the 3d electrons in Cu 0.75VS 2 disappears in the case of Cu 0.65VS 2.

Knight shifts and magnetic susceptibilities of the intermetallic compounds CeCu 4 and CeCu 5

The magnetic susceptibility and Knight shift of the compounds CeCu 4 and CeCu 5 have been measured over the temperature ranges 80–800 and 140–400 K, respectively. The most important contributions to the magnetic susceptibility are the Curie-Weiss term, expressing the paramagnetism of the localized ƒ-electrons, and a temperature independent term, which have both been determined. The phenomenological exchange integral F sƒ between the 4ƒ-electron spins and conduction electron spins was found to be −10.43× 10 −3 eV for CeCu 4 and 3.9 × 10 −3 eV for CeCu 5. A reversal in the sign of the s−ƒ coupling for CeCu 5 is noted.

NMR and magnetic susceptibility of Gd 2Cu 6Al 11 and Gd 2Co 6Al 11 intermetallic compounds

27Al Knight shifts and the magnetic susceptibilities of Gd 2Cu 6Al 11 and Gd 2Co 6Al 11 are reported. The contributions to the magnetic susceptibility are Curie-Weiss terms expressing the paramagnetism of the localized f and d electrons of Gd and Co atoms, and a temperature-independent term. The phenomenological exchange constant γ sf between 4 f-electron spins and conduction electron spins in both the compounds is derived to be −1.26 × 10 −3 eV. In the Gd 2Co 6Al 11 system the Co moment couples with the 27Al nucleus through two mechanisms: (1) through direct overlap between the Co 3 d orbitals and the Al core electrons, leading to core polarization, and (2) through conduction electron polarization. The corresponding phenomenological exchange constants γ i sd and γ e sd are derived to be −0.0375 and 1.33 × 10 −3 eV, respectively.

Magnetic susceptibility ofα-phase CuAu and dilute magnetic CuAu(Fe) alloys

The magnetic susceptibilities of a series of $\ensuremath{\alpha}$-phase CuAu and dilute magnetic CuAu(Fe) alloys with Fe (\ensuremath{\le} 760 ppm) have been measured at six different magnetic fields in the range from 3.95 to 12.75 kOe and over the temperature range from 1.5 to 300 K. The excess susceptibility attributed to Fe in the Fe-bearing CuAu samples was evaluated by comparison with the results of measurement on similar CuAu samples. We separate the single-impurity from impurity-impurity interaction effects in the part of the total susceptibility attributable to the Fe additions. In this treatment, the high-temperature excess susceptibility data are fitted to the expression $\ensuremath{\chi}(H,T)={\ensuremath{\chi}}_{0}+\frac{C}{(T+\ensuremath{\Theta})}+{C}_{2}[\frac{J{B}_{J}(\frac{H}{T})}{H}]$ that consists of a constant ${\ensuremath{\chi}}_{0}$, a Curie-Weiss term, and a single Brillouin-function term. The low-temperature single-impurity susceptibility ${\ensuremath{\chi}}_{s}$ is obtained by the use of the coefficients ${\ensuremath{\chi}}_{0}$ and ${C}_{2}$ in the expression ${\ensuremath{\chi}}_{s}=\ensuremath{\chi}(H,T)\ensuremath{-}{\ensuremath{\chi}}_{0}\ensuremath{-}{C}_{2}[\frac{J{B}_{J}(\frac{H}{T})}{H}]$. The single-impurity term ${\ensuremath{\chi}}_{s}$ is field independent. The interaction effect of parallel-coupled-spin impurities which contribute to the field dependence of the measured susceptibility is explained by a single Brillouin function with $J=3$. The effective Bohr magneton ${\ensuremath{\mu}}_{\mathrm{eff}}$ was found to be $(3.4\ifmmode\pm\else\textpm\fi{}0.1){\ensuremath{\mu}}_{B}$ for all Fe-bearing samples. The pair concentration ${C}_{\mathrm{pair}}$ deduced from the coefficient ${C}_{2}$ appears to be independent of Au concentration and has a magnitude of $(68\ifmmode\pm\else\textpm\fi{}14){C}_{\mathrm{Fe}}$. Indications are that the characteristic temperature ${T}_{c}$, obtained from the relation, $\ensuremath{\Theta}=1.25 {T}_{c}$, depends on both Au and Fe concentration. The existence of a universal relation for ${\ensuremath{\chi}}_{s}$ has been found in which ${T}_{c}$ acts as a scaling temperature with the values of 13.6, 12.2, 10.6, 9.6, and 9.6 K for the alloys with Au concentrations of 0, 2.4, 4.8, 10.0, and 10,8 at.% and Fe concentrations of 750, 450, 440, 350, and 760 ppm, respectively.

Structural defects and magnetic properties in the ordered compound CoGa

The magnetic susceptibility of the β-phase CoGa has been correlated with the defect structure of this phase. If only vacancies on the Co-sublattice (i.e. T-atom sublattice) and Co-atoms on the Ga-sublattice (i.e. transition antistructure atoms or TAS-atoms) are considered, their concentrations can be evaluated by density measurements combined with lattice constant determination. The susceptibility consists of a Curie-Weiss term which can be explained by magnetic moments located at TAS-atoms. The effective local magnetic moment per TAS-atom is found to be (5.02±0.06)μ B . This value is independent of alloy composition and of heat treatment and is valid in the whole composition range for alloys quenched from 900°C as well as for those annealed after quenching or cooled slowly from high temperatures. With annealing out of quenched-in TAS-atoms the susceptibility decreases as predicted by this model.

NMR and magnetic susceptibility of CeCu6

NMR and magnetic susceptibility of CeCu6 intermetallic compound were investigated. The most important contributions to the magnetic susceptibility are the Curie-Weiss term, expressing the paramagnetism of the localized f-electrons, and a temperature independent term for which all the contributions were estimated. The phenomenological exchange constantJsf between 4f — electron spins and conduction — electron spins is derived to be −0·012 eV. The Knight shift and Curie temperature are discussed in terms of the Ruderman-Kittel-Kasuya-Yosida theory and in the Rocher's virtual bound states model. The s — f exchange integralΓ and the Fermi wavevectorkF are derived to be — 0·8 eV and 1·32 A−1, respectively.

Magnetic characteristics of lanthanide-copper compounds with CeCu6structure

Abstract The magnetic susceptibilities of RCu6 compounds (R = rare earth) have been measured over the temperature range 80–1200°K. The contributions to the magnetic susceptibility are the Curie—Weiss term, expressing the para-magnetism of the localized f-electrons and a temperature-independent term for which all the contributions have been estimated. The most important contribution to the temperature-independent term is given by an enhanced Pauli paramagnetism. An expression is proposed for calculating the enhancement factors of the Pauli paramagnetism. The anomalous behaviour of the SmCu6 compound results mainly from Van Vleck-type paramagnetism, and could adequately be calculated on the basis of free Sm3+ ions, as in the case of the compound SmAl3 (de Wijn, van Diepen and Buschow 1967).

Electrical and Magnetic Properties of TiO and VO

The cubic compounds $\mathrm{Ti}{\mathrm{O}}_{x}$ and $\mathrm{V}{\mathrm{O}}_{x}$ have a broad homogeneity range with $x$ varying from about 0.75 to 1.30 and a total vacancy content varying between 11 and 20%. Golden $\mathrm{Ti}{\mathrm{O}}_{x}$ is a typical metal with a temperature- and composition-independent resistivity of about 3 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}3}$ \ensuremath{\Omega} cm, a Seebeck coefficient varying from +1 to -10 \ensuremath{\mu}V/\ifmmode^\circ\else\textdegree\fi{}C, a susceptibility of less than ${10}^{\ensuremath{-}4}$ emu/mole and a superconducting transition temperature between 0.4 and 1.0 K for all compositions. $\mathrm{V}{\mathrm{O}}_{x}$ behaves in a qualitatively similar manner for $x<1.0$. However, it exhibits semiconductor behavior for $x>1.0$, where its resistivity is highly temperature and composition dependent with an activation energy ($150<T<300$ K) rising to about 4 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}2}$ eV for $x=1.3$. The Seebeck coefficient curve of $\mathrm{V}{\mathrm{O}}_{x}$ is sigmoid, with $\ensuremath{\alpha}$ increasing from -12 to + 22 \ensuremath{\mu}V/\ifmmode^\circ\else\textdegree\fi{}C as $x$ increases from 0.8 to 1.3. The magnetic susceptibility can be described by using a temperature-independent susceptibility and a Curie-Weiss term. $\mathrm{V}{\mathrm{O}}_{x}$ is not a superconductor above 0.3 K for any composition. The total number of vacancies in these compounds can be reduced as much as 22% by annealing at 1300\ifmmode^\circ\else\textdegree\fi{}C at pressures of about 60 kbar. This decrease in vacancy concentration is accompanied by a decrease in resistivity and Seebeck coefficient. The superconducting transition temperature of $\mathrm{Ti}{\mathrm{O}}_{x}$ is increased to as high as 1.0 K. Although $\mathrm{Ti}{\mathrm{O}}_{x}$ samples as normally prepared by arc melting are cubic with random vacancies at low temperatures, related ordered structures can be produced by annealing certain compositions at atmospheric pressure. Annealing samples with $x=1.0$ below the transition temperature of 900\ifmmode^\circ\else\textdegree\fi{}C produces an ordered monoclinic structure whose properties are discussed.

Magnetic properties of Au4V

Ordered Au4V has a coercive force of 23 kOe at 4.2°K. The paramagnetic susceptibility includes beside the Curie-Weiss term, a Pauli paramagnetism contribution. A ferromagnetic moment of 0.80 microB/V at. deduced from a localized model agrees with some experimental values.

Electrocaloric effect in potassium dihydrogen phosphate

Measurements of the electrocaloric effect from 78 to 130 K were made on crystalline KH <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> PO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> and are discussed in terms of the phenomenological theory of Devonshire and others. The predicted quadratic dependence of the electrocaloric effect upon applied field (and polarization) in the paraelectric phase was shown to occur; however, the constant of proportionality involved coincided with the value computed from Curie-Weiss law only at the highest temperatures. The electrocaloric effect in the ferroelectric phase was found to be approximately a linear function of the applied field provided the low-field irreversible region of hysteresis was ignored. Values of the spontaneous polarization were determined from the electro-caloric measurements and found to be in good agreement with the values obtained by extrapolating the hysteresis loops to zero field. If the Curie-Weiss term in the Devonshire free-energy expansion is retained when the crystal is in its ferroelectric phase, then evidently a single Devonshire function will not describe KH <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> PO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> in both the ferroelectric and paraelectric phases.