Showing papers on "Curie–Weiss law published in 2019"

Curie-Weiss behavior of liquid structure and ideal glass state.

Abstract: We present the results of a structural study of metallic alloy liquids from high temperature through the glass transition. We use high energy X-ray scattering and electro-static levitation in combination with molecular dynamics simulation and show that the height of the first peak of the structure function, S(Q) − 1, follows the Curie-Weiss law. The structural coherence length is proportional to the height of the first peak, and we suggest that its increase with cooling may be related to the rapid increase in viscosity. The Curie temperature is negative, implying an analogy with spin-glass. The Curie-Weiss behavior provides a pathway to an ideal glass state, a state with long-range correlation without lattice periodicity, which is characterized by highly diverse local structures, reminiscent of spin-glass.

Generalized Curie-Weiss Model and Quadratic Pressure in Ergodic Theory

Abstract: We explain the Curie Weiss model in Statistical Mechanics within the Ergodic viewpoint. More precisely, we simultaneously define in {−1, +1} N , on the one hand a generalized Curie Weiss model within the Statistical Mechanics viewpoint and on the other hand, quadratic free energy and quadratic pressure within the Ergodic Theory viewpoint. We show that there are finitely many invariant measures which maximize the quadratic free energy. They are all Dynamical Gibbs Measures. Moreover, the Probabilistic Gibbs measures for generalized Curie Weiss model converge to a determined combination of the (dynamical) conformal measures associated to these Dynamical Gibbs Measures. The standard Curie Weiss model is a particular case of our generalized Curie Weiss model. An Ergodic viewpoint over the Curie Weiss Potts model is also given.

Local Semicircle Law for Curie-Weiss Type Ensembles

Abstract: We derive and compare various forms of local semicircle laws for random matrices with exchangeable entries which exhibit correlations that decay at a very slow rate. In fact, any $l$-point correlation will decay at a rate of $N^{-l/2}$. We call our ensembles \emph{of Curie-Weiss type}, and Curie-Weiss($\beta$)-distributed entries are admissible as long as $\beta\leq 1$.

Magnetic and Magnetotransport Characteristics of Cr-Substituted Ni 55 Mn 34 Sn 11 Thin Films Grown by Magnetron Sputtering

Abstract: Highly oriented Cr-substituted Ni55Mn34Sn11 Heusler thin films having thickness ~ 400 nm were deposited by Ultrahigh vacuum dc magnetron sputtering on MgO (100) substrates. At room temperature, the films exhibit a mixture of dominant L21 cubic austenite phase, as revealed by the intense (002) and (004) peaks, along with small fraction of the orthorhombic–martensitic phase. Surface morphology of the thin films showed distribution of Cr-rich and Cr-deficit regions together with patterned and aligned magnetic domains, thus bringing out the inherent room temperature ferromagnetism of the film. At temperatures above the Curie temperature, TC ~ 321 K, the magnetic behaviour of the films is seen to follow the Curie law rather than the Curie–Weiss law. Ferromagnetic to antiferromagnetic transition appears at TN ~ 247 K, which gives rise to exchange bias at low temperatures due to the coexistence of the two magnetic orders. This phase coexistence also leads to the formation of a spin glass state deep into the martensitic region. The film exhibits metal-like nature at high temperature and semiconductor-like behaviour with the lowering of temperature. A reentrant metallic state is observed at T ≤ 38 K during cooling that persists up to ≤ 62 K in warming cycle. The hysteresis in the ρ–T curve spread over a very wide temperature range confirms the magnetic phase coexistence in the martensitic state in the present thin films. The magnetoresistance (MR) first increases (2.4% at 300 K and H = 50 kOe) with temperature and maximizes to around ~ 3.25% at T = 150 K and then starts decreasing. Its value in the glassy state is very small. This shows that a magnetic liquid like state is more conducive to larger MR.

The Impurity Magnetic Susceptibility of Semiconductors in the Case of Direct Exchange Interaction in the Ising Model

Abstract: The numerical simulation was applied to study the temperature dependence of the impurity magnetic susceptibility. The direct exchange interaction of the impurity magnetic moments randomly distributed in space was considered within the Ising model. When the temperature in a system decreases, the magnetic susceptibility behavior in this system ceases to comply with the Curie law, which is associated with the formation of a spin glass phase. It is shown that the expression of the preexponential factor in the formula for the direct exchange interaction considerably influences the temperature dependence of the magnetic susceptibility only in the case of ferromagnetic exchange.

Magnetic Properties of Ru-Doped Nd 0.67 Sr 0.33 Mn 1−x Ru x O 3 (0 ≤ x ≤ 0.10) Manganites

Abstract: The structural and magnetic properties of polycrystalline Nd0.67Sr0.33Mn1−xRuxO3 (x = 0.00 and 0.10) samples have been studied with the substitution of Ru at Mn site. The samples have orthorhombic crystal structure determined by room-temperature X-ray diffraction and Rietvield analysis. On Ru doping at Mn site, a change in its symmetry space group is observed. The increase in Ru content significantly affects the Curie temperature (Tc). The double-exchange mechanism is suppressed with Ru doping affecting the Mn3+–O2−–Mn4+ ion network. Paramagnetic regime of samples in magnetization-temperature graph is fitted and analyzed with Curie-Weiss law. The magnetization versus applied magnetic field measurements show that the samples exhibit ferromagnetic behavior at lower temperatures and paramagnetic behavior at room temperature with negligible hysteresis loop and low coercive field.

Evolution of structural and magnetic behavior of SrRuO3 by Ga doping at Ru site

Abstract: Here, we report the study of structural and magnetic behavior of SrRuO3 by Ga doping at Ru site. SrRuO3 has an orthorhombic structure of Pbnm symmetry that has not changed by Ga doping, however, lattice parameters has decreased. The SrRuO3 is the one and only example of 4d based itinerant ferromagnet (FM) in oxides with transition temperature (Tc) ∼ 160 K. Below Tc, SrRuO3 shows large bifurcation between Zero-field-cooled (ZFC) and field-cooled (FC) magnetization, which decreases by Ga doping. The inverse susceptibility (χ−1) in paramagnetic (PM) and high-temperature region shows that the Curie temperature (θp) as well as effective moment decreases by Ga doping. The isothermal magnetization at 5 K shows hysteresis, which retain by Ga doping though the moment decreases. The Arrott plot confirms the FM nature and gives spontaneous magnetization (MS) that decreases by Ga doping.

Magnetic Properties of Disordered Li 2 Co 2 – x Ni x (MoO 4 ) 3 (0 ≤ x ≤ 2) System with a Lyonsite Structure

Abstract: We report on the magnetic properties of disordered Li2Co2 – xNix(MoO4)3 (0 ≤ x ≤ 2) system with a lyonsite structure, where Li+, Ni2+, and Co2+ ions are distributed in a disordered manner in the trigonal prism and octahedral sites. All compositions were found to exhibit paramagnetic behavior at high temperature; the magnetic susceptibility was described by the modified Curie-Weiss law. The experimental effective moments were explained by spin and orbital contributions of the Co2+ ions and only the spin contribution for Ni2+ ions. The negative Curie-Weiss temperature θ indicates the existence of antiferromagnetic coupling for all compositions. At low temperature, the compounds with Co2+ ions (x = 0, 1, 1.6, and 1.8) exhibit a weak ferromagnetic state below 4 K due to intrinsic canting of antiferromagnetically coupled lattices. The compound containing only Ni2+ ions, Li2Ni2(MoO4)3, exhibits a pure antiferromagnetic behavior.

Fluctuation of the free energy of Sherrington-Kirkpatrick model with Curie-Weiss interaction: the paramagnetic regime

Abstract: We consider a spin system with pure two spin Sherrington-Kirkpatrick Hamiltonian with Curie-Weiss interaction. The model where the spins are spherically symmetric was considered by \citet{Baiklee16} and \citet{Baikleewu18} which shows a two dimensional phase transition with respect to temperature and the coupling constant. In this paper we prove a result analogous to \citet{Baiklee16} in the "paramagnetic regime" when the spins are i.i.d. Rademacher. We prove the free energy in this case is asymptotically Gaussian and can be approximated by a suitable linear spectral statistics. Unlike the spherical symmetric case the free energy here can not be written as a function of the eigenvalues of the corresponding interaction matrix. The method in this paper relies on a dense sub-graph conditioning technique introduced by \citet{Ban16}. The proof of the approximation by the linear spectral statistics part is taken from \citet{Banerjee2017}.

Reminiscence of a Magnetization Plateau in a Magnetization Processes of Toy-Model Triangular and Tetrahedral Clusters

Abstract: We discuss magnetization curves of a toy-model trigonal and tetrahedral clusters. Nonlinearity of magnetization with local minimum of differential susceptibility resembling known magnetization plateaus of triangular-lattice and pyrochlore lattice antiferromagnets is observed at intermediate temperature range J ≲ T ≲ Θ (here, J is the exchange coupling constant and Θ is a Curie–Weiss temperature). This behavior is due to increased statistical weight of the states with intermediate total spin of the cluster, which is related to the “order-by-disorder” mechanism of plateau stabilization of a macroscopic frustrated magnet.