Spin Compensation Temperature Research Articles

Phase transitions of a mixed spin ferrimagnet in high temperatures

In this research paper molecular mean field theory (MMFT) has been investigated based on Gibbs-Bogoliubov free energy function of a ferromagnetic mixed spin-3 and spin-5/2 Blume-Capel model with different magnetic crystal fields. The free energy of the proposed ferrimagnet has been evaluated depending on the trial Hamiltonian operator. Minimizing the free energy, one may induce characteristic features of the longitudinal magnetizations, phase transitions and spin compensation temperatures, in the ranges of low temperatures, respectively. In particular, we study the effect of crystal field domains on the critical phenomena for the proposed model. The sublattice magnetization dependence of freerenergy function has been discussed as well. Our results predict the existence of multiple spin compensation sites in the disordered Blume-Capel Ising system for a simple cubic lattice.

Phase transitions of a mixed spin ferrimagnet in high temperatures

In this research paper molecular mean-field theory (MMFT) has been investigated based on Gibbs-Bogoliubov free energy function of a ferrimagnetics mixed spin-3 and spin-5/2 Blume-Capel model with different magnetic crystal fields. The free energy of the proposed ferrimagnet has been evaluated depending on the trial Hamiltonian operator. Minimizing the free energy, one may induce characteristic features of the longitudinal magnetizations, phase transitions and spin compensation temperatures, in the ranges of low temperatures, respectively. In particular, we study the effect of crystal field domains on the critical phenomena for the proposed model. The sublattice magnetization dependence of free energy function has been discussed as well. Our results predict the existence of multiple spin compensation sites in the disordered Blume-Capel Ising system for a simple cubic lattice.

Ferrimagnetic Characteristics and Spin Compensation Temperatures of a Mixed Spin-3 and Spin-5/2 Blume–Capel Model

We study the molecular mean-field theory (MMFT) based on the Gibbs–Bogolyubov free energy function of a ferrimagnetic with mixed spin-3 and spin-5/2 for various magnetic crystal fields in the Blume–Capel model. We have evaluated the free energy depending on the trial Hamiltonian operator. By minimizing the free energy of the present system, we have obtained the characteristic features of the longitudinal magnetizations, compensation temperatures, and re-entrant behaviors in the ranges of low temperatures. In particular, we study the effect of magnetic anisotropies on the critical phenomena for the proposed model. The sublattice magnetization dependence of the free energy function has been discussed as well. Our results predict the existence of multiple spin compensation points in the disordered Blume–Capel system for a square lattice.

Electronic, magnetic, reentrant and spin compensation phenomena in Fe2MnGa Heusler alloy

First principles calculations of structural and magnetic properties of the Fe2MnGa Heusler alloy with face-centered cubic, have been studied using a full potential linearized augmented plane wave within the density-functional theory. Partial and total magnetic moments of Fe, Mn and Ga have been determined as well the bulk modulus using the generalized gradient approximation proposed by Wu and Cohen. Ferromagnetic interactions between next-nearest neighbors, (Fe-Fe, Mn-Mn; JFe-Fe > 0 and JMn-Mn > 0) in addition to the ferrimagnetic Fe-Mn (JFe-Mn < 0) within FMG Heusler alloy are considered. Fe2MnGa exhibits spin compensation temperatures and a first-order reentrant behavior. The studied system undergoes a first-order phase transition between an ordered ferrimagnetic to a paramagnetic. Transition TC, compensation TComp and first order phase transition, Tt points have been determined using Monte Carlo simulation; they are around 750, 400, 684 K, respectively. Magnetic hysteresis cycle has been found for different temperatures; it has been 190, 210 and 230 K.

Ground-State Phase Diagram of a Mixed Spin-3/2 and Spin-7/2 Ising Model: A Study of Complex [Cr(CN)4(μ-CN)2Gd(H2O)4-(bpy)]n.4nH2O.1.5nbpy

In this work, the phase transitions, for a molecular-based magnet, are examined using mean field method (MFM). The longitudinal magnetizations can be achieved by minimizing the free energy is an interesting function for locating and induction of spin compensation temperatures as well. By applying Blume-Capel (BC) configuration to a system consisting of two sublattices for a mixed spin-3/2 and spin-7/2on a square lattice in the anisotropies plane, the ground-state phase diagram of this system has been built. On principles of Bogoliubov inequality (BI) of the free energy, it has been investigated the spin compensation phenomena. In particular, characteristic ferrimagnetic features have been shown depending on an unequal crystal field parameters (DA, DB<-1.0) applied on the A−sites and B−sites, respectively.

Microscopic and mesoscopic understanding of magnetization compensation phenomenon in ferrimagnetic Li0.5FeCr1.5O4 spinel

Structural and magnetic properties of the spinel compound, Li0.5FeCr1.5O4, have been investigated using dc magnetization, neutron depolarization, and neutron diffraction techniques. DC magnetization measurement at 200 Oe has revealed a ferrimagnetic ordering at 417 K and a negative magnetization state between the two compensation temperatures (TComp) of 244 and 256 K. TComp varies with an applied magnetic field and two TComp merge at 256 K for magnetic fields ≥ 500 Oe. The existence of zero domain magnetization around TComp is evident from full recovery of the transmitted neutron beam polarization in a neutron depolarization study. The Rietveld refinement of the neutron diffraction pattern at 430 K reveals that the compound possesses a face centred cubic structure with Fe0.81Li0.19 and Cr1.5Li0.31Fe0.19 as cation distributions at the tetrahedral and octahedral sites, respectively. A temperature dependent neutron diffraction study reveals that the net magnetic moment changes sign near 265 K, across the spin compensation temperature. Both neutron diffraction and mean field calculation show that an asymmetric variation of the sublattice moments as a function of temperature yields a dominance of the ordered tetrahedral site moment over the octahedral site moment below TComp, and vice versa above TComp, and gives a microscopic understanding of the observed magnetization reversal phenomenon. The achieved understanding of magnetization compensation and the high coercivity near TComp have implications for possible use of such ferrimagnetic materials with finite spin polarization as effective spin polarizers/analyzers in spintronic devices.

Reentrant and spin compensation phenomena in an Ising type ferrimagnetic system

A mixed spin-1 and spin-2 Ising ferrimagnetic system is investigated on a square lattice of spins S=±2,±1,0 and Q=±1,0 in the presence of an h′ external magnetic field, such that S and Q are nearest-neighbors antiferromagnetically coupled. Using Monte Carlo simulations we calculate the finite temperature phase diagrams of the magnetization and the specific heat. We consider ferromagnetic interactions between next-nearest neighbors, S spins (J2′), as well as between the Q spins (J3′), and crystal field and external magnetic field interactions at each point of the lattice. Under these conditions the system exhibits spin compensation temperatures and a first-order reentrant behavior in a certain range of the parameters of the Hamiltonian. We analyze the behavior of the critical and compensation temperatures, as well as the first order phase transition temperatures, with the external magnetic and crystal fields, and the next-nearest neighbors interaction between S spins. We found that the existence of compensation temperatures and a first order phase transition depends on the strength of h′, J2′ and D′.

Spin Compensation Temperatures in the Monte Carlo Study of a Mixed Spin-3/2 and Spin-1/2 Ising Ferrimagnetic System

The magnetic properties of mixed-spin S′ = 3/2 and S = 1/2 ferrimagnetic system have been studied by Monte Carlo simulations. The ground-state phase diagrams of mixed spin-3/2 and spin-1/2 Ising system are given. The critical and compensation temperatures have been found with different values of reduced exchange interactions. The variation of total magnetization with reduced exchange interactions of mixed spins is given with different temperatures and crystal fields. We have also given the variation of total magnetization with crystal field for different reduced exchange interactions and different temperatures. The magnetic hysteresis cycle is found to have different values of reduced exchange interactions, temperatures, and crystal fields. The multiple hysteresis and the superparamagnetic phase are established.

Spin compensation temperature in the Monte Carlo study of a mixed spin-1 and spin-3/2 Ising ferrimagnetic system on the decorated triangular lattice

Mixed-spin-1 and spin-3/2 Ising model on the decorated triangular lattice is studied by the use of Monte Carlo simulation. Within this approach, the results for the ground-state of the antiferromagnetic and ferromagnetic of decorated triangular lattice are obtained. The reduced transition temperature of each sublattice are obtained. The reduced temperature of compensation is also obtained. The thermal total ratio of magnetic susceptibilities of sublattices is given. The effect of crystal field and exchange interactions on the magnetization of the system are detailed. The magnetic hysteresis cycles are found for different values of exchanges interactions between the same lattice and the two sublattices different, for different crystal filed and temperatures. In addition, very weak exchange interactions and for a higher temperatures and a higher crystal filed values the decorated triangular lattice has been exhibited the superparamagnetic behavior.

Spin compensation temperatures in the Monte Carlo study of a mixed spin-2 and spin-5/2 Ising ferrimagnetic system

The thermomagnetic properties of a Ising ferrimagnetic system on a bipartite square lattice of spins SiA=2 and σjB=5/2 with different single-ion anisotropies are analyzed by Monte Carlo simulations. We obtained the phase diagrams at finite temperature of the total magnetization (MT), the magnetization of sublattices (MA,MB), specific heat (C) and the total susceptibility (χT) per spin of the model. In the planes (D1/|J1|/kBT/|J1|) and (D2/|J1|/kBT/|J1|) the critical and compensation temperatures have been deduced. We found that single-ion anisotropy interactions play an important role for the existence of compensation temperatures. Compensation points may be present, for a specific range of crystal field of sublattice spins σjB=5/2, even when the anisotropy field of sublattice spins SiA=2 is zero. Mean field theory predicts a wide range of parameters where the system presents even several compensation temperatures, in most of these regions we found none.

Spin compensation temperatures induced by longitudinal fields in a mixed spin-3/2 and spin-5/2 Ising ferrimagnet

I studied the ferrimagnetic Ising model with nearest neighbour interactions for a square lattice and simple cubic one, using mean field theory. The free energy of a mixed spin Ising ferrimagnetic model was calculated from a mean field approximation of the Hamiltonian. By minimizing the free energy, I obtained the equilibrium magnetizations and the compensation temperatures. Clear indications of the single-ion anisotropies on the compensation points of the mixed spin-3/2 and spin-5/2 ferrimagnetic lattices are found. Some interesting behaviors of these systems are obtained depending not only on the values of magnetic anisotropies for both sublattice sites but also on the lattice structure. The longitudinal magnetic fields dependence of the spin compensation temperature is the main focus of research. The possibility of many compensation temperatures is indicated.

Spin compensation temperatures in the mean-field approximation of a mixed spin-2 and spin-5/2 Ising ferrimagnetic system

The magnetic behaviors of a mixed spin-2 and spin-5/2 Ising ferrimagnetic system on a square lattice are studied with the mean-field approximation (MFA) based on the Bogoliubov inequality for the free energy. A Landau expansion of the free energy in the order parameter is also described in this work. In particular, we investigate the effect of a single-ion anisotropy on the compensation phenomenon.

AMagnetic control of spin reorientation and magnetodielectric effect below the spin compensation temperature in TmFeO3

The onset of antiferromagnetic transition, spin reorientation, and spin compensation of TmFeO3 single crystals were investigated by the magnetic and heat capacity measurements. Control of spin reorientation by magnetic field and anomalous hysteretic behavior in domain switching were clarified. No appreciable magnetodielectric effect was observed in spin reorientation temperature region. On the other hand, below the spin compensation temperature both a dielectric anomaly along the c axis and a concomitant magnetodielectric effect up to ∼4% at 80kOe were observed. This suggests that rare-earth orthoferrites can be another candidate for magnetodielectric system through the mediation of spin compensation phenomena.

Study of the magnetic structure in the spinel oxides MnGa xFe 1−xCrO 4 by neutron diffraction

Magnetic properties of the spinel system MnGa x Fe 1− x CrO 4 have been investigated using neutron diffraction (ND) technique in the temperature range 600 K⩾ T⩾10 K. The distribution of the magnetic moments in the tetrahedral (A) and octahedral (B) sublattices and their ordering as a function of temperature and composition has been determined. Ferrimagnetic transition temperatures and spin compensation temperatures have been determined for all the specimens. The features observed in the ND results are explained in the light of competing inter and intra-sublattice exchange interactions. A diffuse signal was found to exist below the innermost Bragg reflection with a general increase with increasing compositions indicating the formation of short-range spin clusters.

The study of magnetic ordering in the spinel system Zn xNi 1− xFeCrO 4 by neutron diffraction

Neutron diffraction measurements have been performed in the temperature range 600 K⩾ T ⩾10 K on the spinel system Zn x Ni 1− x FeCrO 4 ( x=0.2, 0.4, 0.6 and 0.8) synthesized in the ceramic sintering method. The moment distributions in the two sublattices and their ordering as affected by compositional change and temperature variation have been determined. Ferrimagnetic transition temperatures and spin compensation temperatures for all the specimens have been determined. The system shows significant deviations from the usual ferrimagnetic behavior, which increases with the increase of diamagnetic substitutions, being more prominent in the B sublattice. The ferrimagnetic ordering is perturbed due to the presence of non-collinear spins mainly in the B site. Presence of small fluctuating magnetic clusters for x⩾0.6 is evident from the diffuse nature of the scattered intensity. A qualitative explanation of the observed features is put forward in the light of competing inter and intra sublattice exchange interactions. A randomly canted ferrimagnetic ordering is suggestive for the system at x⩽0.4, while a semi-spin glass like transition is favorable for x⩾0.6 due to large reduction in moment and evolution of diffuse signal from short-range clusters at low temperatures.

Ferrites. What Is New?

AbstractFor Abstract see ChemInform Abstract in Full Text.

Ferrites — what is new?

Ferrites, combining insulating and ferrimagnetic properties, have long been used in technology. The aim of this paper is to focus on new features in these materials. In the classical theory of ferrimagnets, Neel had predicted the unusual thermal variation of the spontaneous magnetization, such as, the disappearance of the magnetization at a temperature which was not the Curie temperature but at a point where there was compensation of the spontaneous magnetization of the two sublattices. We show experimentally that temperature (T K) in spinel oxide is different under the ZFC and FC magnetization method. To our knowledge, only limited attempt has been made to study T K as very few systems exhibit such behavior. In general, some of the ferrites have specific semiconducting properties, e.g., a very low carrier mobility. We discuss the anomalies of the magneto-resistance in ferrites that occur at order-disorder and order-order magnetic phase transition along with our ac and dc conductivity data near the spin compensation temperature. Another notable feature of the ferrites is that, upon irradiation of heavy ions, one can tune the magnetic ordering on bulk sample without destructive effects, i.e., irradiation-induced magnetization. It is interesting to note that spinel ferrite (nano) particle is an ideal small particle magnetic system as the crystal chemistry issue can be controlled, unlike pure metal particle systems where the crystal chemistry issues are basically fixed. In relevance to this, we will also discuss the future prospects, namely, the effect of irradiation on small particle magnetism, as, so far, only a limited attempt has been made in this field.

Magnetic properties of Fe 2Mo 1− xTi xO 4

We report the synthesis and characterisation of the spinel oxide Fe 2Mo 1− x Ti x O 4 (x = 0 to 1). The substitution of Ti in Fe 2MoO 4 shows interesting features in the Field Cooled and Zero Field Cooled magnetisation data. We observed a strong negative remanence and spin compensation temperature below Curie temperature. The results suggest the role of Mo in the double exchange interaction with systematic variation of T C with increasing Ti concentration. Field Cooled and Zero Field Cooled data measured under same field shows different compensation temperatures where the magnetic moment is minimum. Also applying a negative field resulted in the negative image of the same magnetisation.

Temperature Dependence of the Magnetic Compton Profile of Ferrimagnetic HoFe2

Circularly polarised synchrotron radiation has been used to measure the spin-dependent magnetic Compton profile of the ferromagnet HoFe 2 at six temperatures from 10 K to 300 K. The magnetic Compton profiles have been analysed using appropriate free atom Compton profiles and a free electron Compton profile which has allowed the determination of the individual spin moments on the Ho and Fe sites and the diffuse moment; the last two are, to a first approximation, temperature independent. The Ho moment, which is antiferromagnetically coupled to them, reduces by a factor of two across the temperature range, leading to a spin compensation temperature of 210±10 K. The experiments were performed with 45.9 keV photons at the KEK ARNE-1 station of the Accumulation Ring.

Compton scattering studies of the temperature dependence of the spin moment in HoFe2.

Compton scattering studies, performed at the KEK accumulation ring in Japan with circularly polarized synchrotron radiation, have been used to determine the spin-dependent Compton profile of ${\mathrm{HoFe}}_{2}$ at temperatures between 10 and 300 K. The holmium spin moment, which is antiferromagnetically coupled to that on the Fe sites, softens as the temperature rises leading to a reversal of the net spin direciton. This has been observed directly and the spin compensation temperature has been estimated from the Compton data to be 210\ifmmode\pm\else\textpm\fi{}10 K.