Spontaneous Magnetization Research Articles

Spontaneous Magnetization of Kagome Lattice in Ising Model

Spontaneous Magnetization of Kagome Lattice in Ising Model

Proposal for a micromagnetic standard problem: Domain wall pinning at phase boundaries

We propose a novel micromagnetic standard problem calculating the coercive field for unpinning a domain wall at the interface of a multiphase magnet. This problem is sensitive to discontinuities in material parameters for the exchange interaction, the uniaxial anisotropy, and the spontaneous magnetization. We derive an explicit treatment of jump conditions at material interfaces for the exchange interaction in the finite-difference discretization. The micromagnetic simulation results are compared with analytical solutions and show good agreement. The proposed standard problem is well-suited to test the implementation of both finite-difference and finite-element simulation codes.

Soft Magnetic Nanocrystalline Ni-Fe-X-Y and MeFe2O4 Powders Obtained by Mechanosynthesis

"The soft magnetic nanocrystalline powders, alloys (Ni3Fe, 79Ni16Fe5Mo, 77Ni14Fe5Cu4Mo, wt. %) and zinc ferrite, were obtained by dry and wet mechanical alloying and reactive milling, followed by different heat treatments. The powders were characterised by X-ray diffraction, scanning electron microscopy, X-ray microanalysis, differential scanning calorimetry, thermomagnetic and magnetic measurements. The X-ray diffraction shown the progressive new phases formation. The crystallite size is between 18-7 nm depending on materials and milling conditions. The particle size is smaller for wet-mechanical alloying comparing with dry-milling. The thermomagnetic measurement shown the Curie temperature of the alloys. The spontaneous magnetisation of the wet-milled and annealed samples is higher than of the molten alloys. Keywords: mechanical alloying; Ni-Fe-X-Y alloys; soft ferrite; magnetisation; XRD; DSC. "

Zigzag nanoribbon of gated bilayer hexagonal crystals with spontaneous edge magnetism

Zigzag nanoribbons of monolayer graphene-like two-dimensional materials host spontaneous edge magnetism at the zigzag terminations, whose configuration controls the band gap. In this article, the edge magnetism of zigzag nanoribbons of bilayer hexagonal crystals are studied. The specific models of bilayer graphene and bilayer silicene are both studied. As the gated voltage increases, the total energy level, magnetic structure and band structures of the ground state and the first quasi-stable excited state are tuned. For certain region of the gated voltage, the band gaps of spin up and down are opened and closed, respectively, so that the systems are in the spin-polarized metallic phase. The spin-polarized conducting edge band of the bilayer nanoribbons could be applied for gate tunable spintronic devices.

A-Site Cation Size Effect on Structure and Magnetic Properties of Sm(Eu,Gd)Cr0.2Mn0.2Fe0.2Co0.2Ni0.2O3 High-Entropy Solid Solutions.

Three high-entropy Sm(Eu,Gd)Cr0.2Mn0.2Fe0.2Co0.2Ni0.2O3 perovskite solid solutions were synthesized using the usual ceramic technology. The XRD investigation at room temperature established a single-phase perovskite product. The Rietveld refinement with the FullProf computer program in the frame of the orthorhombic Pnma (No 62) space group was realized. Along with a decrease in the V unit cell volume from ~224.33 Å3 for the Sm-based sample down to ~221.52 Å3 for the Gd-based sample, an opposite tendency was observed for the unit cell parameters as the ordinal number of the rare-earth cation increased. The average grain size was in the range of 5–8 μm. Field magnetization was measured up to 30 kOe at 50 K and 300 K. The law of approach to saturation was used to determine the Ms spontaneous magnetization that nonlinearly increased from ~1.89 emu/g (Sm) up to ~17.49 emu/g (Gd) and from ~0.59 emu/g (Sm) up to ~3.16 emu/g (Gd) at 50 K and 300 K, respectively. The Mr residual magnetization and Hc coercive force were also determined, while the SQR loop squareness, k magnetic crystallographic anisotropy coefficient, and Ha anisotropy field were calculated. Temperature magnetization was measured in a field of 30 kOe. ZFC and FC magnetization curves were fixed in a field of 100 Oe. It was discovered that the Tmo magnetic ordering temperature downward-curve decreased from ~137.98 K (Sm) down to ~133.99 K (Gd). The spin glass state with ferromagnetic nanoinclusions for all the samples was observed. The <D> average and Dmax maximum diameter of ferromagnetic nanoinclusions were calculated and they were in the range of 40–50 nm and 160–180 nm, respectively. The mechanism of magnetic state formation is discussed in terms of the effects of the A-site cation size and B-site poly-substitution on the indirect superexchange interactions.

Spontaneous magnetization and electroweak phase transition in the scalar sector of 2HDM

We discuss theoretical and phenomenological aspects of the two­-Higgs­-doublet extensions of the Standard model. In modern notation the h2HDM is the model with mh = 125.26 GeV, where the lightest neutral scalar particle in 2HDM is the usual Higgs boson in Standard Model.&#x0D; The parametric space of this model is very rich and admits many scenarios of New Physics’ phenomenol­ogy.The many restrictions and conditions should be satisfied. One of them is the Sakharov’s conditions for the formation of the baryon asymmetry of the Universe in models with extra scalar fields. We try to show that we can satisfy them in the h2HDM and find the region of parametric space where the electroweak phase transition is first order. The Sakharov’s conditions are not satisfied in Standard Model but it is fundamental problem of modeling the Universe, so the searching of New physics this way is relevant.

Spin interactions and topological magnonics in chromium trihalide CrClBrI

The discovery of spontaneous magnetism in van der Waal (vdW) magnetic monolayers has opened up an unprecedented platform for investigating magnetism in purely two-dimensional systems. Recently, it has been shown that the magnetic properties of vdW magnets can be easily tuned by adjusting the relative composition of halides. Motivated by these experimental advances, here we derive a model for a trihalide CrClBrI monolayer from symmetry principles and we find that, in contrast to its single-halide counterparts, it can display highly anisotropic nearest- and next-to-nearest neighbor Dzyaloshinskii-Moriya and Heisenberg interactions. Depending on the parameters, the DM interactions are responsible for the formation of exotic chiral spin states, such as skyrmions and spin cycloids, as shown by our Monte Carlo simulations. Focusing on a ground state with a two-sublattice unit cell, we find spin-wave bands with nonvanishing Chern numbers. The resulting magnon edge states yield a magnon thermal Hall conductivity that changes sign as function of temperature and magnetic field, suggesting chromium trihalides as a candidate for testing topological magnon transport in two-dimensional noncollinear spin systems.

Critical behavior of quasi-2D organic-inorganic halide perovskite (C6H5CH2CH2NH3)2CuCl4 single crystals

Critical behavior of quasi two-dimensional organic-inorganic halide perovskites (C6H5CH2CH2NH3)2CuCl4 is investigated using magneto-thermal and isothermal magnetic properties along the easy axis. Banerjee's criterion indicates that phase transition from paramagnetic to ferromagnetic phases below TC = 9.4 K is of second-order. Scaling analysis reveals that critical exponent β from spontaneous magnetization in the critical region below TC and δ from critical isotherm at TC are found to be 0.22(3) and 9.28–9.4, close to 2D finite XY model. Meanwhile, γ from magnetic susceptibility in the critical region above TC is gradually decreased from 2.4 at high-temperature region. Critical exponents from magneto-thermal properties are found to be consistent with those determined from magnetization isotherms. The reliability of critical values is verified using the scaling hypothesis. Our results evidence that (C6H5CH2CH2NH3)2CuCl4 crossovers from isotropic 2D Heisenberg to anisotropic 3D models towards TC and can be promising candidates for magnetocaloric materials for hydrogen reliquefaction.

Insights into Magnetic Properties of a Mixed Spin-Electron Model on Decorated Planar Lattices Composed of Half-filled Trigonal Bipyramids

A mixed spin-electron model on decorated planar lattices formed by corner-sharing trigonal bipyramids is exactly solved by imposing three mobile electrons per triangular cluster of each bipyramid by means of a generalized decoration-iteration mapping transformation. It is shown that the ground state of the model involves two spontaneously long-range ordered phases, namely, the classical phase with a perfect ferromagnetic arrangement of all particles and the macroscopically degenerate quantum one. The macroscopic degeneracy of the quantum phase lies in chiral degrees of freedom of the mobile electrons. Finite-temperature phase diagrams as well as temperature variations of the spontaneous magnetization, entropy, and specific heat clearly prove that the classical spin-electron arrangement is thermally almost twice more stable than the quantum one for some combinations of the model's parameters.

General solution of spin-1 Ising model in the effective field theory approximation: critical temperatures and spontaneous magnetization

ABSTRACT The system of two polynomial equations is derived for direct simultaneous determination of the critical temperatures of the spin-1 Ising model on lattices with arbitrary values of the coordination number in the single-site cluster effective field theory approximation. Analysis of the critical temperatures allows to determine simple linear function that approximates the critical temperatures of the model with very high precision for all values of the coordination number z. It is demonstrated that the system of two equations for the critical temperatures of the model can be reduced to the corresponding single equation in the cases with and 5. In addition, the system of entirely algebraic polynomial equations for the determination of the spontaneous magnetization of the model simultaneously for all values of the coordination number is also derived and discussed.

Crystallographic, electronic and magnetic properties of Sr2FeW1-xMoxO6 double perovskite oxides

The structural, electronic and magnetic properties of Sr2FeW1-xMoxO6 with 0 ≤ x ≤ 0.3 are studied. Powder samples have been elaborated using the conventional solid - state reaction at 1300 °C. At room temperature our systems are single phase and crystallized in the tetragonal structure with the P4 space group. The Sr2FeWO6 possesses the metallicity ground state and antiferromagnetic ordering. Sr2FeW0.5Mo0.5O6 possesses the half metallicity ground state and ferromagnetic ordering. The difference energy ΔE between the magnetic configurations EFM and EAFM was calculated for x = 0, x = 0.25 and x = 0.5. The Mo doping in W atom leads to the half metallicity and ferromagnetic behavior. This result is confirmed by experimental. Magnetization measurements and calculations exhibit a paramagnetic-ferromagnetic transition. Sr2FeWO6 is antiferromagnetic at low temperature. The Curie temperature and spontaneous magnetization increase with increasing the value of x. The experiments results obtained are comparable with those obtained by simulations.

Landau mean-field analysis of magnetic entropy change and spontaneous magnetization estimation in Nd0.6Sr0.3K0.1MnO3 perovskite

Landau mean-field analysis of magnetic entropy change and spontaneous magnetization estimation in Nd0.6Sr0.3K0.1MnO3 perovskite

Impurity effect on hysteric magnetoconductance: holographic approach

In this paper we study a hysteric phase transition from weak localization phase to hysteric magnetoconductance phase using gauge/gravity duality. This hysteric phase is triggered by a spontaneous magnetization related to ℤ2 symmetry and time reversal symmetry in a 2+1 dimensional system with momentum relaxation. We derive thermoelectric conductivity formulas describing non-hysteric and hysteric phases. At low temperatures, this magnetoconductance shows similar phase transitions of topological insulator surface states. We also obtain hysteresis curves of Seebeck coefficient and Nernst signal. It turns out that our impurity parameter changes magnetic properties of the dual system. This is justified by showing increasing susceptibility and the spontaneous magnetization with increasing impurity parameter.

Behavior of thermally quenched topological defects in quasicrystal artificial spin ices

Understanding the formation of topological defects in connected magnetic nanowires such as in artificial spin ices (ASIs) is critical to controlling their behavior. Moreover, emergent frustration behavior of these defects can be expected due to complex underlying lattice geometry of the ASIs. We have explored in situ thermalization and quenching of quasicrystalline ASIs, which exhibit additional frustration due to aperiodicity from near the Curie temperature, and we observe the formation of two sets of topological vortex defects: within the magnetic bars and within the vertices at which the bars meet. By varying the laser fluence, we show that the number of defects in the vertices varies as the quenching rate changes following a power law relation, which we interpret as being related to the ferromagnetic-to-paramagnetic phase transition. Conversely, the defects formed within the bars are metastable states related to the spontaneous magnetization reversal of the magnetic bars and are therefore strongly dependent on underlying lattice geometry. These results provide insight into the emergence and control of topological defects in confined frustrated magnetic systems.

Paramagnetic spin Hall magnetoresistance

Spin Hall magnetoresistance (SMR) refers to a resistance change in a metallic film reflecting the magnetization direction of a magnet attached to the film. The mechanism of this phenomenon is spin exchange between conduction-electron spins and magnetization at the interface. SMR has been used to read out information written in a small magnet and to detect magnetization dynamics, but it has been limited to magnets; magnetic ordered phases or instability of magnetic phase transition has been believed to be indispensable. Here, we report the observation of SMR in a paramagnetic insulator Gd$_{3}$Ga$_{5}$O$_{12}$ (GGG) without spontaneous magnetization combined with a Pt film. The paramagnetic SMR can be attributed to spin-transfer torque acting on localized spins in GGG. We determine the efficiencies of spin torque and spin-flip scattering at the Pt/GGG interface, and demonstrate these quantities can be tuned with external magnetic fields. The results clarify the mechanism of spin-transport at a metal/paramagnetic insulator interface, which gives new insight into the spintronic manipulation of spin states in paramagnetic systems.

Multiferroic, Phonon and Optical Properties of Pure and Ion-Doped YFeO3 Nanoparticles

The magnetic, electric, phonon and optical properties of pure and ion-doped orthorhombic YFeO nanoparticles are studied for the first time theoretically. The spontaneous magnetization in YFeO decreases with decreasing particle size. is also shape dependent. The magnetization increases by Co and Er ion doping and decreases by Ti doping, which is caused by the different strain which appears in the nanoparticles and changes the exchange interaction constants in the doped states. The phonon energy for the mode = 149 cm and their damping decreases or increases with increasing temperature, respectively. Both show a kink near the Neel temperature, , which disappears by applying an external magnetic field. The influence of different ion doping on the band gap energy is also discussed. The doping effects can be used for different applications.

Spontaneous magnetization reversal and positive exchange bias effect in CoFeSiB/FeCrO3 heterostructures

The exchange bias (EB) phenomenon is an interface-driven effect; it depends on the interface spin configuration, which in turn is immensely related to antiferromagnetic spin configuration. Here, we chose an antiferromagnet, FeCrO3, with a corundum structure with randomly occupied cations. We report EB in the bilayer heterostructures that are composed of an amorphous CoFeSiB ferromagnet interfaced with an epitaxial FeCrO3 layer fabricated in-situ by pulsed laser deposition. The bilayers exhibit crossover from conventional negative EB to positive EB from room temperature down to 5 K. The crossover occurs for a cooling field that exceeds the interfacial coupling strength at the interface. Systems that show positive EB effects sometimes also display spontaneous magnetization reversal; the present bilayers showed spontaneous EB below 50 K. Temperature and field-dependent magnetisation studies reveal that the prepared heterostructure consists of uncompensated interface spins due to the disorder in the FeCrO3 layer that gets frozen at low temperatures, pins the spins in the ferromagnetic layer and causes the spontaneous EB effect.

Nuclear spin-lattice relaxation time in UCoGe

The NMR measurements performed on a single orthorhombic crystal of superconducting ferromagnet UCoGe (Y.Ihara et al, Phys. Rev. Lett. v.105, 206403 (2010)) demonstrate strongly anisotropic magnetic properties of this material. The presented calculations allow to establish the dependence of longitudinal spin-lattice relaxation rate from temperature and magnetic field. The value 1/T_1T in field perpendicular to spontaneous magnetisation directed along c-axis has maximum in vicinity of Curie temperature whereas it does not reveal similar behaviour in field parallel to the direction of spontaneous magnetisation. Also there was shown that the longitudinal spin-lattice relaxation rate is strongly field dependent when the field directed in b-crystallographic direction but field independent if magnetic field is oriented along a-axis.

Lifshitz scaling effects on the holographic paramagnetic-ferromagnetic phase transition

We disclose the effects of Lifshitz dynamical exponent z on the properties of holographic paramagnetic-ferromagnetic phase transition in the background of Lifshitz spacetime. To preserve the conformal invariance in higher dimensions, we consider the Power-Maxwell (PM) electrodynamics as our gauge field. We introduce a massive 2-form coupled to the PM field and perform the numerical shooting method in the probe limit by assuming the PM and the 2-form fields do not back-react on the background geometry. The obtained results indicate that the critical temperature decreases with increasing the strength of the power parameter q and dynamical exponent z. Besides, the formation of the magnetic moment in the black hole background is harder in the absence of an external magnetic field. At low temperatures, and in the absence of an external magnetic field, our result show the spontaneous magnetization and the ferromagnetic phase transition. We find that the critical exponent takes the universal value \(\beta = 1/2\) regardless of the parameters q, z, d, which is in agreement with the mean field theory. In the presence of an external magnetic field, the magnetic susceptibility satisfies the Curie-Weiss law.

Epitaxial-Strain-Induced Spontaneous Magnetization in Polar Mn2Mo3O8

Epitaxial-Strain-Induced Spontaneous Magnetization in Polar Mn₂Mo₃O₈