Temperature Dependence Of Spontaneous Magnetization Research Articles

Determination of effective magnon mass of neodymium magnet by temperature dependence of spontaneous magnetization

The effective mass of a magnon in a neodymium magnet is evaluated using Bloch temperature dependence of spontaneous magnetization. We use the Hall effect magnetometer and thermo-couple thermometer for measurement of the temperature of the water in which the encapsulated commercial magnet is immersed. The experiment can be repeated in every school and methodological remarks for experimental data processing are given with great detail and attention. The purpose of the paper is to illustrate the simple relation between the quantum spectrum of magnons and the easily measured magnetic field of a permanent magnet.

Magnetic and Ferromagnetic Resonance Studies in Amorphous Co–Zr Films

The magnetic properties of amorphous Co[Formula: see text]Zrx films prepared by co-evaporation have been studied by means of vibrating sample magnetometry and ferromagnetic resonance. The temperature dependence of spontaneous magnetization [Formula: see text] in the low temperature range can be described using Bloch’s law. In addition, the spin wave stiffness constant, the distance between nearest magnetic atoms and the exchange interaction between cobalt and its nearest neighbors were calculated from the experimental results for [Formula: see text]. Spin-wave resonance modes were obtained and the change of the resonant field as a function of the mode number [Formula: see text] obeys the so-called [Formula: see text] law perpendicular to the film plane at 300[Formula: see text]K.

Interpretation of Fe-rich part of Fe–Al phase diagram from magnetic properties of A2-, B2-, and DO3-phases

Iron-rich Fe–Al binary phase diagram in the composition range of 23–26 at% Al shows a complex structure partly due to magnetic properties of the disordered A2-phase, the ordered B2-phase and the ordered DO 3 -phase. In this study, the disorder-order transformations between the constituent phases have been investigated through magnetization measurements of Fe- x Al alloys ( x = 22.0, 24.0, 24.3, 24.7, 26.5 at%). It is found that spontaneous magnetization of the B2-phase is larger than that of the DO 3 -phase and smaller than that of the A2-phase. The former relation disagree with previous reports but was further confirmed as the decrease of the B2-DO 3 transformation temperature under magnetic field (−1.58 K/T). It is also found that the Curie temperature of the B2-phase (836 K for Fe-24.7 at%Al alloy) coincides with that of the A2-phase; furthermore, these temperatures agree with the phase boundary between B2-region and (A2+B2)-region. • Temperature dependence of spontaneous magnetization was evaluated for the A2-, B2- and DO3-phases of Fe24.7at%Al alloy, and found that the value decreases in this order at any temperature. • Magnetic field dependence of B2-DO3 transformation temperature was evaluated for several Fe-Al alloys, and confirmed that it decreases as magnetic field increases. • Critical behavior for the magnetic transition was analyzed for several Fe-Al alloys and revealed that Curie temperature of the B2-phase almost coincides with that of the A2-phase.

Spontaneous Spin Reorientation in Gd–Co Amorphous Films

The phenomenon of spontaneous spin reorientation in Gd–Сo amorphous films, which results from the competition between the perpendicular magnetic anisotropy and shape anisotropy, is studied. It is shown that the reorientation occurs via the formation of a fine-grained nonuniform magnetic structure called hypercritical state in a wide temperature range. Magnetic domains in the spin-reorientation region are characterized using magnetic and magneto-optical measurements. Based on the experimental magnetometric data and results of simulating the temperature dependences of spontaneous magnetization, the phase diagram of the films containing 16–26 at % Gd is constructed, which, being plotted on coordinates elemental composition—temperature, exhibits the ranges of existence of the perpendicular anisotropy, transition magnetic anisotropy (hypercritical state), and planar magnetization state.

Magnetocaloric effect and critical behaviour of La0.5Ca0.2Ag0.3MnO3 compound

We present a dc magnetization study of the critical phenomena of a manganite oxide La0.5Ca0.2Ag0.3MnO3 single crystal. Based on the assumption of a continuous (second order) manganite transition for our sample, we have determined the critical temperature Tc = 264 K and the critical exponents β=0.18259±0.004 (β: critical exponent for the temperature dependence of spontaneous magnetization just below TC), γ=0.81967±0.0.029 (γ: critical exponent for the inverse initial susceptibility just above TC) and δ=5.45±0.006 (δ: critical exponent for the Widom scaling relation (T = TC)). From the field dependence of the magnetic entropy ΔSMΔSM∝Hn and the relative cooling power (RCP) RCP∝H∧1+1/δ, it was possible to evaluate the critical exponents of the magnetic phase transitions. Their values are in good agreement with those obtained from the critical exponents using a modified Arrott method.

Monte Carlo Modeling of Magnetic Phase Transitions in Amorphous Alloys of the Re–Gd System

A Monte Carlo study of the magnetic properties of simulated amorphous alloys of the Re–Gd system is performed using the Heisenberg model. The temperature dependences of spontaneous magnetization, magnetic susceptibility, and the Edwards–Anderson order parameter are calculated. The dependence of the temperature of the transition to the spin-glass state on the concentration of gadolinium atoms is constructed. The transition to the spin-glass state in Re–Gd amorphous alloys occurs only above the percolation threshold in this system.

Hirschfeld surface analysis and short-range ferromagnetic ordering in La0.5Ca0.4Ag0.1MnO3 based on critical behavior study

We investigated the Hirschfeld surface analysis and critical behaviour in La0.5Ca0.4Ag0.1MnO3 near the second-order ferromagnetic phase transition at Curie temperature TC. We determined the critical exponents, β, γ and δ corresponding to the temperature dependence of spontaneous magnetization, initial susceptibility and isothermal magnetization, respectively. The study of Hirshfeld surface reflects that both the electrostatic and intermolecular interactions are short range. The values for critical exponents obtained from magnetic measurements are very close to those predicted by the mean field tri-critical model. The critical-exponent values deduced here were in a good conform to those obtained using the modified Arrott plot and Widom scaling relation.

Effect of substrate temperature on magnetic properties of MnFe2O4 thin films

MnFe2O4 thin films were pulsed laser deposited on to quartz substrate from room temperature (RT) to 650 °C in a pure argon environment. Temperature dependence of spontaneous magnetization (4πMS) was measured on these films from 10 K to 350 K using a vibrating sample magnetometer. Ferromagnetic resonance (FMR) study was also carried out at 300 K. The exchange stiffness constant (D) values were obtained by fitting the 4πMS data to the Bloch’s equation. The D values of the films thus found decreases while the 4πMS value increases, though non-monotonically, with the increase in TS and tend to reach bulk values at TS = 650 °C. The variation in D and 4πMS values of the films are explained based on the degree of inversion and oxidation state of cations in thin films.

Giant magnetoresistance and correlation between critical behavior and electrical properties in a new compound La0.6Gd0.1Sr0.3Mn0.8Si0.2O3 manganite

We investigated the influence of silicone (Si) doping on the structural, magnetic and electrical properties of polycrystalline sample La0.6 Gd0.1 Sr0.3 Mn0.8 Si0.2 O3 (LGSMSiO), prepared by sol–gel method. The crystallographic study showed that the sample crystallizes in orthorhombic system with Pnma space group. The relationship between the electrical and magnetic properties of manganites was traced through analyzing the dependence of LGSMSiO resistivity on temperature. The measurement of resistivity versus the temperature ρ(T) showed a transition change from ferromagnetic (FM) to paramagnetic (PM) at Curie temperature (TC), this usually accompanied by a simultaneous metal-semiconductor (M-semiconductor) transition. Resistivity decreased with increasing the applied magnetic field. The values of TM-semiconductor were found to move towards a high temperature side with increasing the magnetic field. The critical properties of electron doped manganite LGSMSiO were investigated on the data of static magnetization measurements around the second order ferromagnetic-paramagnetic transition region TC. The magnetic data analyzed in the critical region using Kouvel-Fisher method yield the critical exponents of γ=1.013±0.02 with TC=270.69±0.22K (from the temperature dependence of inverse initial susceptibility above TC) and β=0.2535±0.0032 with TC=269.89±0.12K (from the temperature dependence of spontaneous magnetization below TC). The critical magnetization isotherm M(TC, μ0H) gives δ = 5.01 ± 0.03. The critical exponents found in this study obeyed the Widom scaling relation: δ = 1+γ/β, implying that the obtained values of γ and β are reliable.The exponents values obtained from resistivity were quite close to those predicted by the tricritical mean-field model. These results were in good agreement with the analysis of the critical exponents from magnetization measurements. The electrical resistivity was fitted with the phenomenological percolation model, which is based on the phase segregation of the ferromagnetic metallic regions and the paramagnetic semiconductor regions. So, we found that the estimated results were in accordance with the experimental data. The magnetocaloric value is 5.35 J/kgK, extracted from the M(μ0H) curves.

Spin-wave excitations and magnetism of sputtered Fe/Au multilayers

The spin-wave excitations and the magnetism of Fe/Au multilayers with different Fe thicknesses (t Fe) grown by RF sputtering were investigated. The temperature dependence of spontaneous magnetization is well described by a T3/2 law in all multilayers in the temperature range of 5–300 K. Spin-wave theory has been used to explain the temperature dependence of the spontaneous magnetization and the approximate values for the exchange interactions for various t Fe were obtained. The spin-wave constant B was found to increase linearly with the inverse in the Fe thickness (1/t Fe). Using the ferromagnetic resonance technique, the change of the anisotropy field H K as a function of 1/t Fe was deduced. The spatial distributions of the discrete spin-wave modes were calculated. All the extracted results were in agreement with those determined experimentally and found in the literature.

Diluted Ising Magnet on the Bethe Lattice

A solution is obtained for the Ising model on the Bethe lattice comprising a mixture of magnetic and nonmagnetic atoms in a thermodynamic equilibrium. The concentration and temperature dependences of spontaneous magnetization, the Curie temperature, and the percolation threshold are found together with the pair correlation functions of three types that characterize the arrangement of impurity atoms and the correlation of magnetic moments. It is demonstrated that the system with mobile impurities in the thermodynamic equilibrium can be brought closer to the system with frozen impurities by adjusting the parameters of interatomic interaction.

Magnetic order of Au nanoparticle with clean surface

Au nanoparticles, which are kept in vacuum after the preparation by gas evaporation method, show ferromagnetism even in 1.7nm in diameter. The intrinsic magnetism is examined by detecting the disappearance of spontaneous magnetization in Au bulk prepared by heating the nanoparticles without exposure to the air. The temperature dependence of spontaneous magnetization is not monotonic and the increase in magnetization is observed after Au nanoparticles are exposed to the air. The magnetic behavior can be interpreted by the ferrimagnetic-like core–shell structure with shell thickness of 0.16±0.01nm and magnetic moment of (1.5±0.1)×10−2μB/Au atom, respectively.

Critical behavior and magnetic entropy change at magnetic phase transitions in Ni50Mn35In14Si1 ferromagnetic shape memory alloy

We have investigated critical behaviour and magnetocaloric effect in polycrystalline Ni50Mn35In14Si1 alloy near the second-order ferromagnetic phase transitions (SOPT) at austenite Curie temperature and at martensite Curie temperature by determining the critical exponents, β, γ and δ corresponding to the temperature dependence of spontaneous magnetization, initial susceptibility and isothermal magnetization, respectively. The field dependence of the maximum value of the magnetic entropy change at the two TC's was estimated using the Maxwell relation as well as from the values of the critical exponents. Values of obtained by these two methods at both the SOPT are in remarkable agreement with each other. The critical exponents have been determined by analysing isothermal magnetization data using two different methods, viz., the modified Arrott plot method and the Widom scaling relation. The scaling plots depicted on linear as well as logarithmic scales confirm the reliability of the values of critical exponents obtained. The values of the critical exponents of polycrystalline Ni50Mn35In14Si1 alloy at both the TC's are close to those predicted by mean-field theory confirming the presence of long-range magnetic ordering in the investigated alloy.

Magnetic-field-induced martensitic transformations in Ni47 − x Mn42 + x In11 alloys (with 0 ≤ x ≤ 2)

Magnetic properties and martensitic transformations in the Ni47 − x Mn42 + x In11 alloys (with 0 ≤ x ≤ 2) have been studied. The magnetic-field-induced martensitic transformation was found to be observed for all the alloys. The critical temperatures of magnetic and structural phase transformations, temperature dependences of spontaneous magnetization of austenite and martensite, and the critical field, at which the martensitic transformation occurs, have been determined based on magnetic measurements performed for the alloys under study. The spontaneous magnetization of the alloys in the martensitic state has been shown to be lower than that in the magnetic-field-induced austenitic state by a factor of six.

Magnetic properties of a GdMn6Sn6 single crystal

The magnetization of a GdMn6Sn6 single crystal has been measured in static magnetic fields up to 14T as well as in pulsed fields up to 60T. The easy magnetization direction has been confirmed to lie in the basal plane of the hexagonal crystal, the anisotropy within the plane being negligible. However, our data do not corroborate the earlier assertion that GdMn6Sn6 is a collinear ferrimagnet. This disagrees with the observed field dependence of magnetization along the easy direction as well as with the temperature dependence of spontaneous magnetization. A way out of the contradiction is to admit that GdMn6Sn6 has a more complex, non-collinear magnetic structure.

Computer simulation of magnetization relaxation in amorphous magnetics with random anisotropy

On the basis of Heisenberg model, the magnetic properties of amorphous terbium were studied by the Monte Carlo method. The temperature dependences of spontaneous magnetization and magnetic susceptibility were plotted as functions of the fraction of the constant of anisotropy to the exchange constant D/J0. The behavior of magnetization in an external magnetic field was studied, and the dependence of a coercive field and residual magnetization on the value D/J0 was found. The relaxation of magnetization was investigated after the external magnetic field was switched off.

Simulation of magnetic phase transitions in amorphous alloys of the Re-Gd system

Using the Monte Carlo method within the Heisenberg model, we studied the magnetic properties of amorphous alloys of the Re-Gd system and of pure amorphous gadolinium. The temperature dependences of spontaneous magnetization, magnetic susceptibility, and the Edwards-Anderson order parameter were determined. The possibility of the system transitioning to the spin-glass state was examined.

Strong dependence of ferrimagnetic properties on Na concentration in Na–K alloy clusters incorporated in low-silica X zeolite

Na concentration ( x) dependence of ferrimagnetic properties is investigated for Na–K alloy clusters incorporated in low-silica X (LSX) zeolite. In the LSX zeolite, β-cages of inner diameter ≈7 Å are arranged in a diamond structure, and supercages of inner diameter ≈13 Å are formed among them. The used LSX zeolite contains xNa + and (12− x)K + cations per β-cage or supercage. Guest nK atoms are loaded into the zeolite, namely the loading density is given by n per β-cage. The samples at x=4 have been reported to show Néel’s N-type ferrimagnetism in the specific region of n. This ferrimagnetism is explained by the model of antiferromagnetic coupling between two non-equivalent magnetic sublattices of clusters, the ones in β-cages and the others in supercages. In the present study, the value of x is changed from 4 to 0. Ferrimagnetic properties are found to show strong x-dependence. A systematic increase in loading densities of ferrimagnetic region is clearly observed with decreasing x. A remarkable change in temperature dependence of spontaneous magnetization is observed depending on x. Na + cations are known to be mainly distributed in β-cages. Hence, the decrease in Na concentration is proposed to change the electronic potential depth for clusters in β-cage, which leads to important differences in the interaction between electrons localized in β-cages and those in supercages.

Thermodynamic properties of quasi-equilibrium magnons in crystalline bulk materials and thin films

The temperature dependence of spontaneous magnetization and specific heat for a system of magnons are investigated systematically. The correspondence of this system with the Bose-Einstein condensation phenomenon is used. Calculations are performed for both crystalline bulk materials and thin films. The calculated results are consistent with the available experimental data, indicating that our suggested approach is a suitable one for describing the thermodynamic properties for the magnon system. The thermodynamical parameters for magnons system have many similarities with the thermodynamical parameters for boson atomic gas. Results for crystalline bulk material can be used as a zeroth order approximation in any perturbative treatment of thin film. In contrast to a previous study, our method involves only analytic calculations.

Temperature dependence of the ferromagnetic order parameter in Gd, Tb, and Dy

Temperature dependence of spontaneous magnetization, ${M}_{s}(T)$, corresponding to the single-domain ferromagnetic state, has been studied experimentally using high-purity single crystals of Gd, Tb, and Dy. The resulting ${M}_{s}(T)$ curves follow the ``$3∕2\ensuremath{-}5∕2\ensuremath{-}1∕3$ law.'' Anomalies due to the crystal-field gap and to the helix-ferromagnet transition in Tb and Dy are practically indiscernible.