Showing papers on "Curie–Weiss law published in 1995"

Iron exchange-field penetration into the amorphous interphase of nanocrystalline materials.

Abstract: In this work an enhancement of the Curie temperature of the intergranular amorphous region in nanocrystalline alloys with respect to amorphous ribbons of the same composition is shown. The Curie temperature reaches a value of 125 \ifmmode^\circ\else\textdegree\fi{}C. The experimental results are discussed in terms of both an inhomogeneous distribution of Nb atoms in the interphase and the magnetic interactions between the Fe ferromagnetic grains and the matrix. Finally, it is proposed that the existence of a molecular field of about 80 T originated by the penetration of the exchange field of \ensuremath{\alpha}-Fe nanocrystals into the amorphous paramagnetic intergranular region is the main cause of this Curie temperature enhancement. Moreover, the compositional dependence of the Curie temperature in Fe-B-Nb-Cu amorphous ribbons has been reported.

Magnetic properties of rare-earth metallofullerenes

Abstract: Bulk amounts of La C[sub 82] and Gd C[sub 82] have been isolated in pure form from various hollow fullerenes. Magnetization data for these powder samples, an isolated La C[sub 82] isomer and a Gd C[sub 82] isomer, have been obtained employing a SQUID magnetometer at temperatures ranging from 3 to 300 K. For La C[sub 82] the inverse susceptibility as a function of temperature follows a Curie-Weiss law. The effective magnetic moment per La C[sub 82] is 0.38 [mu][sub B]. For Gd C[sub 32] the magnetization data fall on a universal curve which is fitted to a Brillouin function in correspondence with the Gd[sup 3+] free ion ground state values of J = 3.38 and g = 2. 33 refs., 6 figs.

Magnetoelastic properties and level crossing in HoVO4.

Abstract: The rare-earth oxide compound ${\mathrm{HoVO}}_{4}$ (tetragonal zircon structure) is investigated in the extended susceptibility formalism, which includes all the features of the crystalline electric field in the analysis of the magnetic, magnetoelastic, and elastic properties as a function of temperature. The characteristic behavior of the first-order magnetic susceptibility allows us to refine the values of the crystalline electric-field parameters and to determine the strength of the magnetic interactions. The magnetoelastic coefficients are then found from third-order magnetic susceptibility, parastriction, and elastic-constants measurements for the different symmetry modes. Their coherency with values determined for ${\mathrm{TbPO}}_{4}$ is then emphasized: They have the same sign and order of magnitude; in particular the magnetoelastic coefficients for the tetragonal symmetry are sizable in these rare-earth oxides in contrast to the case of rare-earth intermetallics. The unusual temperature dependence of the third-order magnetic susceptibility along the tetragonal axis is a precursor of the level crossing in high magnetic fields associated with a magnetization jump of about 8${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ at 11.4 T, which we study as a function of temperature down to 0.1 K. The existence of a two-step jump of the magnetization at low temperatures, if not driven by mechanical stresses, remains an intriguing result.

Variation of magnetic properties as a function of Mo content in the RFe12−xMox series and their nitrides (R=Y, Nd, Gd)

Abstract: The structure and magnetic properties of RFe12−xMox series and their nitrides with R=Y,Gd,Nd and x=0.8,1.0,1.5,2.0,2.5 have been studied by x‐ray‐diffraction and magnetic measurements. It is found that with the increment of Mo content x, the lattice parameters increase, whereas the saturation magnetization, Curie temperature, and anisotropy field decreases in the RFe12−xMox series. Upon nitrogenation lattice parameters, saturation magnetization, and Curie temperature increase. Correspondingly, the easy c‐axis magnetocrystalline anisotropy of the Fe sublattice decreases in YFe12−xMoxNy and GdFe12−xMoxNy but increases in NdFe12−xMoxNy although its variation with the Mo content is the same as in their original counterparts. NdFe12−xMoxNy compound in the low Mo content shows great potential for permanent magnet applications.

Magnetization and resistivity of UNi4B in high magnetic fields

Abstract: The hexagonal uranium intermetallic compound ${\mathrm{UNi}}_{4}$B orders antiferromagnetically below ${\mathit{T}}_{\mathit{N}}$=20 K in a magnetic structure, where, in zero applied magnetic field, one-third of the spins remains paramagnetic. Here, we report on the high-field (B\ensuremath{\le}50 T) magnetic and transport properties of this material. We establish the magnetic structures and phase diagram and the influence of magnetic field on the paramagnetic spins. Model calculations of the magnetization assuming two independent spin systems are in qualitative agreement with the observed magnetization.

Phase transition and electron localization in 1t-tas2

Abstract: The magnetic properties and phase transitions of 1T-TaS2 and 1T-Fe0.07Ta0.93S2 have been studied in the interval of 1.5-300 K and over the range of 100 Oe-60 kOe. Experimental results show that at high temperatures the compounds are in a diamagnetic state and the commensurate-charge-density-wave-triclinic-nearly-commensurate transition temperature of 1T-TaS2 decreases with increasing magnetic field. The amount of variation is a function of the magnetic field. At low temperatures both 1T-TaS2 and 1T-Fe0.07Ta0.93S2 are in a paramagnetic state owing to the localized moments that come from the single Anderson-Mott localization state. The curves of magnetization versus temperature do not follow the Curie law or Curie-Weiss law, but can be described fairly well as M = M(0) + gamma T--n. The fitting parameters of experimental curves show that a part of the neighboring moment appears as antiferromagnetic coupling due to exchange interaction between the moments. The magnetic-field dependence of magnetization exhibits a complicated feature at low temperature. It shows that the compounds may undergo a phase transition at the maximum value of magnetization and then they are probably in a mixed charge-density-wave-spin-density-wave (CDW-SDW) state or SDW state due to the coherent superposition of the antiferromagnetic coupling.

Phase relation, crystal structure, and magnetic properties of La-Co-Si alloys

Abstract: mined by means of x-ray powder di6raction In this region there exist four ternary compounds: LaCoSi3, LaCoSi2, LaCoS ie, atomic ordering occurs Magnetic measurements indicate that the tetragonal LaCo» Si intermetallic compounds are ferromagnetic with Curie temperature higher than 900 K and anisotropy fields of about 10 kOe The saturation magnetic moment per Co atom in the tetragonal LaCo» Si„compounds decreases with Si content The composition dependence of the saturation magnetic moment per Co atom can be satisfactorily explained by the rigid-band model

Crystal field effects on thermal and magnetic properties of Er3Co

Abstract: The specific heat and magnetic susceptibility have been measured for Er3Co. The magnetic susceptibility obeys the Curie-Weiss law in the temperature range of 100-300 K with the effective moment µ eff=9.52µ B. A large magnetic specific heat above the Curie temperature of 13 K was found, which is interpreted in terms of the point-charge model. It is revealed that the crystal field and exchange field are of the same order of magnitude and that the electronic thermal excitations contribute to the magnetic specific heat, resulting in a broad Schottky-type contribution. Moreover, magnetocrystalline anisotropy gives rise to the noncollinear spin structure.

Magnetism of the β-phase p-nitrophenyl nitronyl nitroxide crystal

Abstract: The ferromagnetism of β-phase p-nitrophenyl nitronyl nitroxide has been established by various measurements at an ambient pressure. To get further insight into the magnetic interactions, the pressure effect on the magnetic and thermal properties has been examined in the pressure range of 0–7.7 kbar. Important feature of the results is twofold. One is a reduction of the Curie temperature with applied pressure. This suggests that the exchange interactions are mainly responsible for determination of the Curie temperature. Dipolar couplings are estimated to be too small to explain the observed Curie temperature. The other is the lowering of the lattice dimensionality. The heat capacity curve under the pressure of 7.2 kbar coincides with the theory for a two-dimensional Heisenberg ferromagnet above the Curie temperature. This suggests that the interactions between the neighboring ac-plane are more affected by compression of the crystal.

Size Effect in Ferroelectric Long Cylinders

Abstract: The Curie temperature and polarization in a ferroelectric cylinder with infinite length have been examined using Landau free energy expansion. The Curie temperature and polarization decrease with decreasing cylinder diameter for the positive extrapolation length, and reach zero at the critical size. For negative extrapolation length, both Curie temperature and polarization increase with decreasing cylinder diameter.

Magnetic susceptibility measurements in PrBe13

Abstract: The temperature dependent complex magnetic susceptibility of the Van Vleck paramagnet PrBe13 has been measured at temperatures below 20 mK in zero magnetic field. We observe an antiferromagnetic Curie-Weiss behaviour of the nuclear spin susceptibility with a Weiss temperature Θ = -2.2 mK.

High field phase diagram of Nd2−xCexCuO4 single crystals

Abstract: We present high magnetic field ultrasonic and magnetic susceptibility measurements for Nd 2 CuO 4 and Nd 1.85 Ce 0.15 CuO 4 single crystals at temperatures below 2 K. The magnetic field dependences or the c 11 , c 66 acoustic modes and the magnetic susceptibility demonstrate a large number or field induced phase transitions which are reduced in the Ce-doped compound. Using the anomalies in the sound velocity and magnetic susceptibility we obtained the low temperature range or B-T phase diagrams or these compounds for magnetic field applied along the [100] direction