Spontaneous Magnetization Research Articles

Nd3+ induced twofold continuous spin reorientation transition and magnetization along the b-axis in a Dy0.9Nd0.1FeO3 single crystal

An intriguing hybrid magnetic configuration Γ4+3 with non-zero spontaneous magnetization along b-axis was found in DNFO91 single crystal. Contributions of R3+ were distinguished and the relative strength can be manipulated with magnetic field.

Construction of an approximate solution for an Ising magnet in an external magnetic field

A method of approximate calculation of the magnetization of an Ising magnet located in an external magnetic field is proposed. This method is based on using an exact or approximate expression for the spontaneous magnetization of an Ising magnet on the same lattice. The method uses the ratio of effective fields for clusters of one and two lattice nodes. Using the proposed method for a magnet located in an external field, the dependence of magnetization on temperature and the magnitude of the external field is calculated. The proposed method is applied in the work to the solution in the mean field approximation, to the solution in the Beta approximation and to the exact solution on a square lattice; for all these solutions, critical indices characterizing the behavior of a magnet in an external field are calculated. Keywords: the Ising model, phase transitions, the influence of an external field.

First-principles based Monte Carlo modeling of the magnetization of oxygen-deficient Fe-substituted SrTiO3.

Transition-metal (TM) substituted SrTiO3 has attracted much attention because its magnetism and/or ferroelectricity can be tuned via cation substitution, point defects, strain and/or oxygen deficiency. For example, Goto et al. [Phys. Rev. Applied, 7, 024006 (2017)] reported the magnetization of SrTi1-xFexO3-δ (STF) grown under different oxygen pressures and on various substrates. Here, we use hybrid density functional theory to calculate the effects of different oxygen vacancy (VO) states in STF on the magnetization for a variety of Fe cation arrangements. The magnetic states of the cations associated with the VO ground-states for x = {0.125, 0.25} are used within a Monte Carlo model for collinear magnetism to simulate the spontaneous magnetization. Our model captures several experimental features of STF, i.e., an increase in magnetization for small δ up to a maximum of ∼0.35μB per formula unit at an intermediate number of vacancies, with a slower decrease in magnetization with an increasing number of vacancies. Our approach gives insight into the relation between vacancy concentration and the oxygen pressure required to maximize the magnetization.

Spontaneous magnetization of a vacuum in high temperature gluodynamics (two-­loop approximation)

In SU(N) gluodynamics, at high temperature the spontaneous magnetization, b(T) ≠ 0, of a vac­uum happens in the approximation to the effective potential ­- the tree plus the one-­loop, plus daisy diagrams, W(b) = b2/2g2 + W(1)(b) + Wdaisy(b). At the same time, in two­-loop approximation, W(A0) = W(1) (A0) + W(2)(A0), other classical field ­ A0 condensate directly related to the Polyakov loop - ­is also spontaneously generated. To investigate the creation of the condensates together, the two-loop effective po­tential of both fields should be calculated. This program was realized recently for SU(2) in [1]. However, the generation of magnetic field in two­-loop order was not studied in detail. In the present paper, we compute the value of chromomagnetic field b(T) for latter case. Then, considering the spectrum of color charged gluons at the background of both condensates, we conclude that the A0 stabilizes the magnetized vacuum at high temperature. This is in agreement with the lattice simulations carried out already and clarifies the mechanism of the magnetic field stabilization.

Selected properties of surface modified GaxFe3-xO4 with 0≤x≤1.5

ABSTRACT The influence of the surface modification on the magnetism of 4–14 nm sized core and core/shell gallium ferrites obtained by different preparation methods (Massart’s and thermal decomposition from acetylacetonates) was studied. The physical properties of GaxFe3-xO4 were investigated in a wide range of Ga admixtures 0 ≤ x ≤ 1.5. Ga ions location at 8a or/and 16d positions of a spinel structure depends on the synthesis method and has a pronounced effect on the superparamagnetic properties of nanoparticles. Magnetization and Mössbauer experiments show the dominant superparamagnetic contribution for the nanoparticles with x > 0.8 with the blocking temperature TB significantly below 200 K. Surface-modified nanoferrites disclosed spontaneous magnetization that does not exceed 60 emu/g.

Superconducting phase transition reveals an electromagnetic coupling to a scalar field potential that generates mechanical work

Pressure-induced, spontaneous diamagnetism associated with critical behaviour is determined experimentally in a polar dielectric fluid containing nanoscale, clathrate hydrate cage structures. As with Type II superconductivity, Abrikosov vortices come to penetrate the external diamagnetic field such that it reduces to zero for particular values of the magnet flux. The external magnetic field is thus revealed to be the order parameter that signifies a phase transition between Type II superconducting behaviour and a dual of Type I superconducting behaviour. This phase transition is described by a distinctive universality class of critical exponents. The Abrikosov vortices are interpreted as effective magnetic monopole defects associated with the non-equilibrium, geometrically frustrated system. The magnitude of the spontaneous Type I response is consistent with exponential coupling of the spontaneous magnetism with an external scalar field potential made accessible through inertia and hyperbolic geometry. Under this interpretation, magnetic monopole defects act as inhomogeneous nucleation sites able to expand or contract the volume of the system in an analogue of cosmological inflation. The quantum vacuum origin of the scalar field is held responsible for the resulting mechanical work, so representing a potentially unlimited source of zero-emissions energy.

Unconventional Spin State Driven Spontaneous Magnetization in a Praseodymium Iron Antimonide.

Consolidating a microscopic understanding of magnetic properties is crucial for a rational design of magnetic materials with tailored characteristics. The interplay of 3d and 4f magnetism in rare-earth transition metal antimonides is an ideal platform to search for such complex behavior. Here the synthesis, crystal growth, structure, and complex magnetic properties are reported of the new compound Pr3 Fe3 Sb7 as studied by magnetization and electrical transport measurements in static and pulsed magnetic fields up to 56T, powder neutron diffraction, and Mößbauer spectroscopy. On cooling without external magnetic field, Pr3 Fe3 Sb7 shows spontaneous magnetization, indicating a symmetry breaking without a compensating domain structure. The Fe substructure exhibits noncollinear ferromagnetic order below the Curie temperature TC ≈380 K. Two spin orientations exist, which approximately align along the Fe-Fe bond directions, one parallel to the ab plane and a second one with the moments canting away from the c axis. The Pr substructure orders below 40K, leading to a spin-reorientation transition (SRT) of the iron substructure. In low fields, the Fe and Pr magnetic moments order antiparallel to each other, which gives rise to a magnetization antiparallel to the external field. At 1.4K, the magnetization approaches saturation above 40T. The compound exhibits metallic resistivity along the c axis, with a small anomaly at the SRT.

Hexagonal RFeO3 (R = Dy, Er, and Lu) Films Grown on Glass Substrates with Both Magnetic and Ferroelectric Orders

Hexagonal rare-earth ferrites (h-RFeO3) are promising multiferroic materials owing to the spontaneous magnetization, high ferroelectric transition temperature, and fascinating features provided by strong magnetoelectric coupling. However, h-RFeO3 is metastable, and its synthetic methods are limited, particularly when ionic size of R is large. One of useful synthesis methods is epitaxial thin-film growth on single-crystal substrates, because the metastable phase is stabilized by the lattice match between h-RFeO3 and the substrate. Compared to single-crystal substrates, glass substrates are more cost-effective. However, films on glass tend to consist of a thermodynamically stable phase owing to the amorphous nature of glass substrates. Herein, we report that a h-RFeO3 pure phase can be obtained as thin film even on glass substrates. The metastable phase was formed owing to the nonequilibrium synthesis process of pulsed laser deposition. The obtained h-RFeO3 thin films on glass with R = Dy, Er, and Lu exhibited weak ferromagnetism with Néel temperatures of 120–140 K. Furthermore, a clear magnetic phase transition from weak ferromagnetic to antiferromagnetic phase was observed in the h-ErFeO3 films. Additionally, piezoelectric force microscopy measurements exhibited the ferroelectricity of the film at room temperature. These results provide a convenient synthesis method of a pure phase multiferroic h-RFeO3 system.

Observation of griffiths phase and ferromagnetism in LaFe0.5Mn0.5O3

We report the structural and magnetic characterization of the polycrystalline LaFe0.5Mn0.5O3 compound. It crystallizes in an orthorhombic crystal structure with Pnma space group. A systematic investigation of magnetic behavior revealed the antiferromagnetic ordering at 276 K and Griffiths Phase-like behavior in the temperature range of 276 K to 314 K, confirmed by the power-law susceptibility exponent(λ). At a low temperature, spontaneous magnetization (Ms) is due to dominant ferromagnetic interaction. We estimated the magnitude using Arrot plot of different isotherms.

Magnetization Processes in Metallic Glass Based on Iron of FeSiB Type.

In the present paper, the magnetization processes in amorphous alloys based on iron are discussed in detail. Our main goal was to measure the stabilization energy connected with the presence of microvoids (frozen during rapid cooling from the liquid phase) and to determine the interaction energy of relaxators with spontaneous magnetization vector (the so-called wN Neel) for amorphous Fe78Si13B9 alloys. A structural analysis of the alloys using X-ray measurements at the subsequent stages of crystallization was also performed.

Theoretical investigation of the magnetic properties of ferromagnetic CrI3 monolayer

The CrI3 monolayer is the first ferromagnetic two-dimensional material experimentally discovered and the study of its properties is a hot topic. First-principles calculations and experimental measurements show that the CrI3 monolayer is a typical S=3/2 localized magnetic system. In the present work, we investigated the intrinsic magnetic properties of CrI3 monolayer based on the anisotropic Heisenberg model and using the double-time Green’s function method. The Hamiltonian parameter values of CrI3 monolayer are estimated theoretically based on the experimental Curie temperature of CrI3 monolayer and the experimental magnetic parameters of CrI3 bilayers. The spontaneous magnetization and zero-field susceptibility are calculated, and the critical behaviors of the system are analyzed. We observe that the maximum magnetic susceptibility value is sensitive to the isotropic exchange parameter and external magnetic field, but almost independent of anisotropic strengths.

Ising spin glass on random graphs at zero temperature: Not all spins are glassy in the glassy phase

We investigate the replica symmetry broken (RSB) phase of spin glass (SG) models in a random field defined on Bethe lattices at zero temperature. From the properties of the RSB solution we deduce a closed equation for the extreme values of the cavity fields. This equation turns out not to depend on the parameters defining the RSB, and it predicts that the spontaneous RSB does not take place homogeneously on the whole system. Indeed, there exist spins having the same effective local field in all local ground states, exactly as in the replica symmetric (RS) phase, while the spontaneous RSB manifests only on the remaining spins, whose fraction vanishes at criticality. The characterization in terms of spins having fixed or fluctuating local fields can be extended also to the random field Ising model (RFIM), in which case the fluctuating spins are the only responsible for the spontaneous magnetization in the ferromagnetic phase. Close to criticality we are able to connect the statistics of the local fields acting on the spins in the RSB phase with the correlation functions measured in the paramagnetic phase. Identifying the two types of spins on given instances of SG and RFIM, we show that they participate very differently to avalanches produced by flipping a single spin. From the scaling of the number of spins inducing RSB effects close to the critical point and using the $M$-layer expansion we estimate the upper critical dimension $D_U \geq 8$ for SG.

Cavity-induced chiral edge currents and spontaneous magnetization in two-dimensional electron systems

We consider a laterally confined two-dimensional electron gas (2DEG), placed inside a gyrotropic cavity. Splitting of the circularly polarized electromagnetic modes leads to the emergence of the ground state spontaneous magnetization, anomalous Hall effect and chiral edge currents in 2DEG. We examine the dependence of the magnetization and edge current density on the system size for two particular cases of the confining potential: infinite wall and parabolic potentials. We show that paramagnetic and diamagnetic contributions to the edge currents have qualitatively different dependence on the system size. These findings pave the route to the design quantum electrodynamic engineering of the material properties of the mesoscopic electron systems.

Destruction of surface states of (dzx+idyz) -wave superconductor by surface roughness: Application to Sr2RuO4

The fragility of the chiral surface current of ($d_{zx}+id_{yz}$)-wave superconductor, a potential candidate for Sr$_2$RuO$_4$, against surface roughness is demonstrated utilizing the quasiclassical Eilenberger theory. Comparing the chiral surface currents of ($d_{zx}+id_{yz}$)-wave and ($p_{x}+ip_{y}$)-wave pairings, we conclude the chiral current for ($d_{zx}+id_{yz}$)-wave SC is much more fragile than that for the ($p_x+ip_y$)-wave one. The difference can be understood in terms of the orbital symmetry of the odd-frequency Cooper pairs arising at the surface. Our results show the ($d_{zx}+id_{yz}$)-wave scenario can explain the null spontaneous magnetization in Sr$_2$RuO$_4$ experiments.

Possible Kondo scattering and its signature in Seebeck coefficient in topological superconductor Fe1+yTe0.55Se0.45

Fe1+yTe1-xSex is an iconic topological superconductor with Majorana zero mode in the Abrikosov vortex core, holding potential for topological quantum computing. However, the presence of interstitial iron impurities in this system induces spontaneous magnetization, which often hinders access to the intrinsic behavior. Here, we show that in high-quality Fe1+yTe0.55Se0.45 single crystals, no trace of spontaneous magnetization can be found using the highly sensitive Nernst measurement. Instead, a negative magnetoresistance with intriguing temperature and field dependences is observed, with corresponding signatures also found in the magneto Seebeck effect. These observations point to possible Kondo scattering in the normal state of the superconductor originating from the fluctuating magnetic moment of the interstitial irons, which constitute a non-negligible factor in interpreting the low-temperature transport behaviors.

Magnetic properties of NdFe[formula omitted]Ti and YFe[formula omitted]Ti, from experiment and theory

NdFe11Ti and YFe11Ti serve as prototypes for rare-earth (RE) lean or REfree magnets with the ThMn12-type structure. Although NdFe11Ti has been studied for a long time the origin of its complex magnetism at low temperature is so far not well-understood. We present a comprehensive theoretical and experimental study of the magnetic properties of NdFe11Ti and RE-free YFe11Ti to elucidate the influence of the 4f electrons. The partially localized 4f electrons of Nd are the driving force behind the complex behavior of the magnetocrystalline anisotropy which changes from cone to uniaxial above 170 dK. The spontaneous magnetization and the five leading anisotropy constants were determined from high-quality single crystal samples over a wide temperature range using field dependencies of magnetization measured along the principle crystallographic directions. The experimental data are compared with density functional theory combined with a Hartree-Fock correction (+U) and an approximate dynamical mean-field theory.

Zeeman Effect in Centrosymmetric Antiferromagnetic Semiconductors Controlled by an Electric Field.

Centrosymmetric antiferromagnetic semiconductors, although abundant in nature, seem less promising than ferromagnets and ferroelectrics for practical applications in semiconductor spintronics. As a matter of fact, the lack of spontaneous polarization and magnetization hinders the efficient utilization of electronic spin in these materials. Here, we propose a paradigm to harness electronic spin in centrosymmetric antiferromagnets via Zeeman spin splitting of electronic energy levels-termed as the spin Zeeman effect-which is controlled by an electric field. By symmetry analysis, we identify 21 centrosymmetric magnetic point groups that accommodate such a spin Zeeman effect. We further predict by first principles that two antiferromagnetic semiconductors, Fe_{2}TeO_{6} and SrFe_{2}S_{2}O, are excellent candidates showcasing Zeeman splittings as large as ∼55 and ∼30 meV, respectively, induced by an electric field of 6 MV/cm. Moreover, the electronic spin magnetization associated to the splitting energy levels can be switched by reversing the electric field. Our Letter thus sheds light on the electric-field control of electronic spin in antiferromagnets, which broadens the scope of application of centrosymmetric antiferromagnetic semiconductors.

Ferromagnetism of MnO anchored on graphene with N dopant

MnO is a well-known antiferromagnetic transition mental oxide with a wide band gap, the lack of intrinsic ferromagnetism limits its applications in spintronics. Hence, in order to expand the application field of MnO and especially explore the existence of ferromagnetism, we experimentally achieve the N-doped MnO anchored graphene. As is expected, the MnO-based samples exhibit obvious intrinsic room temperature ferromagnetism, which is dependent on the N dopant concentration. Further, density functional theory (DFT) results reveal that the spontaneous magnetization comes from the ferromagnetic double-exchange interaction between Mn atoms with the aid of N dopants.

Evaluation of sedimentary thickness and Curie point depths in the eastern part of Bornu Basin, North-Eastern Nigeria

The Curie point depth is the depths at which subsurface temperature (approximately 580 oC) loses spontaneous magnetization within the rock units and magnetic minerals show features of paramagnetic susceptibility. In this research work sedimentary thickness and Curie point depths of the eastern parts of Bornu basin were investigated. The aeromagnetic data was subdivided into twenty-five (25) overlapping blocks, and each block was analyzed to obtain depth to basement (Zt) of the magnetic sources and depth to centroid (Zo). The depth values were then used to estimate CPD and Curie temperature (𝜃) within the study area. The result shows that the depth to basement (Zt) varies between 2.55 and 7.4 km, with an average value of 5.96 km, the depth to centroid (Zo) values varies between 8.4 and 14.15 km with an average value of 11.08 km, the CPD values varies between 15.11 and 19.0 km with an average value of 16.20 km.

Evidence of ferromagnetic clusters in magnetic Weyl semimetal Co3Sn2S2

Cobalt based sulfides of compositional formula Co3A2S2 (A = Sn and In) are endowed with frustrated kagome lattice structure and a plethora of novel phenomena due to the topological band structure. We report on the detailed exploration of magnetic properties of single crystals of ferromagnetic Weyl semimetal Co3Sn2S2. A non-linear behaviour observed in the inverse susceptibility above the critical temperature TC in the paramagnetic state corroborates to the presence of short-range ferromagnetic clusters above TC in Co3Sn2S2. The upward deviation indicates the antiferromagnetic interactions between the nearest neighbouring magnetic clusters. The slow spin dynamics behaviour above TC in isothermal remanent magnetization provide another evidence of ferromagnetic clusters. The magnetic hysteresis loops represent the magnetization reversal which, in turn, also confirm the short range magnetic correlations. Further, non-linear isothermal magnetization curves and zero spontaneous magnetization derived from corresponding Arrott plots above TC prove the short range ferromagnetic clusters in Co3Sn2S2. Our experimental results emphasize an intuitive understanding of the complex nature of magnetism present in Co-based shandite systems.