Showing papers on "Curie–Weiss law published in 2015"

Structural and magnetic investigations of single-crystalline neodymium zirconate pyrochlore Nd 2 Zr 2 O 7

Abstract: We report structural and magnetic properties studies of large high-quality single crystals of the frustrated magnet ${\mathrm{Nd}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$ Powder x-ray diffraction analysis confirms that ${\mathrm{Nd}}_{2}{\mathrm{Zr}}_{2}{\mathrm{O}}_{7}$ adopts the pyrochlore structure Room-temperature x-ray diffraction and time-of-flight neutron-scattering experiments show that the crystals are stoichiometric in composition with no measurable site disorder The temperature dependence of the magnetic susceptibility shows no magnetic ordering at temperatures down to 05 K Fits to the magnetic susceptibility data using a Curie-Weiss law reveal a ferromagnetic coupling between the Nd moments Magnetization versus field measurements show a local Ising anisotropy along the $\ensuremath{\langle}111\ensuremath{\rangle}$ axes of the ${\mathrm{Nd}}^{3+}$ ions in the ground state Specific heat versus temperature measurements in zero applied magnetic field indicate the presence of a thermal anomaly below $T\ensuremath{\sim}7$ K, but no evidence of magnetic ordering is observed down to 05 K The experimental temperature dependence of the single-crystal bulk dc susceptibility and isothermal magnetization are analyzed using crystal field theory and the crystal field parameters and exchange coupling constants determined

Renormalized anisotropic exchange for representing heat assisted magnetic recording media

Abstract: Anisotropic exchange has been incorporated in a description of magnetic recording media near the Curie temperature, as would be found during heat assisted magnetic recording. The new parameters were found using a cost function that minimized the difference between atomistic properties and those of renormalized spin blocks. Interestingly, the anisotropic exchange description at 1.5 nm discretization yields very similar switching and magnetization behavior to that found at 1.2 nm (and below) discretization for the previous isotropic exchange. This suggests that the increased accuracy of anisotropic exchange may also reduce the computational cost during simulation.

Magnetic Cluster Expansion model for random and ordered magnetic face-centered cubic Fe-Ni-Cr alloys

Abstract: A Magnetic Cluster Expansion (MCE) model for ternary face-centered cubic Fe-Ni-Cr alloys has been developed using DFT data spanning binary and ternary alloy configurations. Using this MCE model Hamiltonian, we perform Monte Carlo simulations and explore magnetic structures of alloys over the entire range of alloy compositions, considering both random and ordered alloy structures. In random alloys, the removal of magnetic collinearity constraint reduces the total magnetic moment but does not affect the predicted range of compositions where the alloys adopt low temperature ferromagnetic configurations. During alloying of ordered fcc Fe-Ni compounds with Cr, chromium atoms tend to replace nickel rather than iron atoms. Replacement of Ni by Cr in alloys with high iron content increases the Curie temperature of the alloys. This can be explained by strong antiferromagnetic Fe-Cr coupling, similar to that found in bcc Fe-Cr solutions, where the Curie temperature increase, predicted by simulations as a function of Cr concentration, is confirmed by experimental observations.

Dependence of Curie temperature on Pt layer thickness in Co/Pt system

Abstract: The Pt thickness dependence of the Curie temperature of perpendicularly magnetized ultra-thin (Pt/)Co/Pt films has been investigated by magnetization measurements. The Curie temperature and the saturation magnetic moment increase with the Co layer thickness and even with the Pt layer thickness. The Curie temperature is found to have linear dependence on the total magnetic moment of the system and the coefficients of the linear fits are almost identical, regardless of whether the thicknesses of the ferromagnetic Co layer or the Pt layer are varied. The Curie temperature also increases with the magnetic anisotropy, but no systematic dependence is observed. These results suggest that the magnetic moment induced in the Pt layer by the ferromagnetic proximity effect plays a significant role in determining the Curie temperatures of such two-dimensional ferromagnetic systems.

Magnetic anisotropy and magnetic domain structure in C-doped Mn5Ge3

Abstract: Magnetic properties of Mn5Ge3C0.7 thin films grown by molecular beam epitaxy have been studied. SQUID-VSM measurements and magnetic force microscopy have been used to probe the magnetic state and determine the relevant magnetic parameters. The results are supported by a combination of improved Saito's and Kittel's models. The moderate perpendicular magnetic anisotropy (Q(exp) - 2K(u)/mu M-0(Sat)2 approximate to 0:2) leads to a stripe domain structure for film thicknesses above 28 nm. For thinner films, the magnetization lies in-plane. The uniaxial magnetocrystalline constant has been found to be much weaker than in Mn5Ge3 and is assigned to hybridization effect between the Mn and C atoms.

Magnetic behavior of the metal organic framework [(CH3)2NH2]Co(HCOO)3

Abstract: In this study we examine the phase transitions in single crystals of [(CH3)2NH2]Co(HCOO)3, using magnetization and specific heat measurements as a function of temperature and magnetic field. Magnetisation measurements indicate a transition at 15 K that is associated with an antiferromagnetic ordering. Isothermal magnetization versus magnetic field curves demonstrate the presence of a single-ion magnet phase, coexisting with antiferromagnetism. A peak in specific heat is seen at 15 K, corresponding to a magnetic transition and the enthalpy of the transition evaluated from the area under the specific heat peak which decreases with the application of a magnetic field of up to 8 T. This is suggestive of long range antiferromagnetic magnetic order, giving way to single-ion magnetic behavior under an external magnetic field. At high temperatures, the specific heat measurements show a peak at ∼155 K that is insensitive to the applied magnetic field. Raman scattering studies confirm the presence of a structural transition. The magnetisation in this temperature range, while exhibiting a paramagnetic behavior, shows a distinct jump and the paramagnetic susceptibility changes across the structural transition.

Measurement of the thermodynamic temperature using a paramagnetic thermometric material

Abstract: It is suggested that thermodynamic temperature T be measured with magnetic susceptibility χ of a colloid solution of single-domain ferromagnet nanoparticles. The magnetic susceptibility is taken as a thermometric parameter, since χ and temperature are related by Curie’s law. It is shown that for Curie’s law to be satisfied, the magnetic susceptibility should be determined from the formula χ = Mμ0/B, where M is the magnetization and B is the mean magnetic induction in the colloid solution. Experimental verification carried out for a magnetite nanoparticle solution in the temperature range 273–373 K shows that when the temperature grows, the Curie constant either remains almost unchanged or increases by several percent. The increase in the Curie constant upon heating can be explained by the decomposition of conglomerates containing nanoparticles with antiparallel magnetic moments.

High-Frequency Electric Properties of Amorphous Soft Magnetic Cobalt-Based Alloys in the Region of Transition to the Paramagnetic State

Abstract: Effect of the temperature on the high-frequency electric impedance of amorphous soft magnetic cobalt-based wires is investigated. A high sensitivity of their impedance to the transition of the ferromagnetic state into the paramagnetic state is demonstrated. The temperature dependences of the impedance measured at different alternating current frequencies allow a distribution of the magnetic phases in the wire volume to be elucidated.

Electric Field Effect on Magnetism in Metallic Ultra-thin Films

Abstract: Recent experimental developments on the electric field effect on magnetism in metallic magnetic materials are reviewed. The change in the electron density at the surface of metallic ultra-thin magnets by the application of an electric field results in modulations of the Curie temperature, magnetic moment, magnetic anisotropy, and domain wall velocity. The study focused on this paper is the electric field effect on the Curie temperature (magnetic phase transition) in Pt/Co ultra-thin film systems. Electric field modifications of the magnetic moment induced by ferromagnetic proximity effects in Pd, which is usually a nonmagnetic element, are also discussed.

Relationship between Curie temperature and Brillouin function characteristics of NiCuZn ferrites

Abstract: Based on Neel's two-sublattice collinear model, the relationship between Curie temperature Tc and temperature characteristics of Brillouin function for NiCuZn ferrites has been studied by nonlinear fitting calculation method. According to the tetrahedral A sites and the octahedral B sites of spinel structure model which do not only contain Fe3+ but also some other multiple magnetic ions (Ni2+and Cu2+), molecular-field coefficients ωaa, ωbb, and ωab = ωba have been calculated; furthermore, the ferrimagnetism and paramagnetism Curie temperature Tc calculation formula has been modified, respectively. The magnetic moment versus temperature T (below the Curie temperature Tc) and the reciprocal of paramagnetism magnetic susceptibility 1/χm versus temperature T (beyond the Curie temperature Tc) have been investigated, respectively. The values of the calculated ferrimagnetism Curie temperature are very close to the values of the testing Curie temperature, and with the same zinc content t, the values of paramagnet...

First-order ferromagnetic transition in single-crystalline (Mn,Fe)(2)( P,Si)

Abstract: (Mn,Fe)2(P,Si) single crystals have been grown by flux method. Single crystal X-ray diffraction demonstrates that Mn0.83Fe1.17P0.72Si0.28 crystallizes in a hexagonal Fe2P crystal structure (space group P6¯2m) at both 100 and 280 K, in the ferromagnetic and paramagnetic states, respectively. Magnetization measurements show that the crystals display a first-order ferromagnetic phase transition at their Curie temperature (TC). The preferred magnetization direction is along the c axis. A weak magnetic anisotropy of K1 = 0.28 × 106 J/m3 and K2 = 0.22 × 106 J/m3 is found at 5 K. A series of discontinuous magnetization jumps is observed far below TC by increasing the field at constant temperature. These magnetization jumps are irreversible, occur spontaneously at a constant temperature and magnetic field, but can be restored by cycling across the first-order phase transition.

Influence of Zr on Structure and Dielectric Behavior of BaTiO 3 Ceramics

Abstract: Barium zirconium titanate ceramics, BaTi1–xZrxO3 (x = 0–15 at % with a step of 2.5%) (BTZx), were obtained by a sol-gel method. Perovskite-like single-phase compounds were confirmed from X-ray diffraction data. Morphological analysis on sintered samples by scanning electron microscopy shows that the addition of zirconium ions affects the growth of the grain and remarkably changes the grain morphology. The effect of zirconium addition to BT on dielectric properties is analyzed. Increasing Zr content in the BaTiO3-based compositions caused a decrease in the Curie temperature (Tc) and the permittivity increases. The Curie-Weiss law is well followed for the pure sample, but it is less respected in the case of BTZ10 and the variation of the Curie Weiss constant as a function of frequency is similar to the variation of the dielectric constant. On the other hand, the application of the modified Uchino law, to the BTZx materials, shows that the diffusio

Curie Temperature Distribution in FePt Granular Media

Abstract: The Curie temperature distribution is an important parameter affecting transition noise in heat-assisted magnetic recording. In this paper, we follow up on our recent report on a technique to evaluate the Curie temperature distribution and provide modeling that validates the method as well as provides the experimental bounds for its validity. Thermal modeling is used to determine whether the technique is sensitive to extrinsic sources of grain temperature variations, such as distributions in thermal boundary resistance. The technique is applied to a variety of FePt granular media films of varying alloy composition and chemical ordering, and we find the Curie temperature distribution to depend primarily on grain ordering kinetics. We also present results of grain switching probability as a function of the applied magnetic field and find a non-trivial dependence on the alloy magnetization.

Temperature Dependence of Minor Hysteresis Loop in NiZn Ferrite Measured by Lock-In Amplifier

Abstract: The detailed BH loop measurements of an NiZn ferrite toroid have been studied at various temperatures below the Curie temperatures $T_{C}$ using a lock-in amplifier. The Jiles–Atherton (JA) analysis of the BH loops gives the power-law relations among the hysteresis parameters and the JA parameters. The Steinmetz analysis suggests the power-law relation proposed by Kobayashi et al. is valid in wide range of the temperature in low magnetic field.