Showing papers on "Curie–Weiss law published in 2014"
TL;DR: Magnetic susceptibility for ferrite Bi25FeO39 was measured at 5−950 K in the magnetic field of 0.86 T as discussed by the authors. But the magnetic moment of Fe3+ ions was not measured.
60 citations
TL;DR: In this paper, a method to measure the switching probability of an ensemble of exchange-decoupled grains with perpendicular anisotropy subject to nanosecond heating pulses is presented.
Abstract: Heat assisted magnetic recording (HAMR) has been recognized as a leading technology to increase the data storage density of hard disk drives. Dispersions in the properties of the grains comprising the magnetic medium can lead to grain-to-grain Curie temperature variations, which drastically affect the jitter in the recorded magnetic transitions and limit the data storage density capabilities in HAMR. Here we present a method to measure the switching probability of an ensemble of exchange-decoupled grains with perpendicular anisotropy subject to nanosecond heating pulses. The short heat exposure time ensures that the grains switch by reaching the Curie temperature rather than through thermal activation. The switching probability can be directly interpreted as representing the Curie temperature distribution. The method is applied to two sets of samples to reveal the sensitivity of the Curie temperature distribution to FePt HAMR media fabrication parameters. This technique is of importance to engineer suitable HAMR media capable of high density magnetic recording and for fundamental studies on sources of magnetic disorder in granular magnetic media.
45 citations
TL;DR: In this paper, the Glauber dynamics for a bi-populated Curie-Weiss model was analyzed and the limiting behavior of the empirical averages in the limit of infinitely many particles was obtained.
Abstract: We analyze the Glauber dynamics for a bi-populated Curie–Weiss model. We obtain the limiting behavior of the empirical averages in the limit of infinitely many particles. We then characterize the phase space of the model in absence of magnetic field and we show that several phase transitions in the inter-groups interaction strength occur.
45 citations
TL;DR: In this article, the magnetocaloric effect and relative cooling power based on the first order magnetic phase transition in Sm 0.55 Sr 0.45 MnO 3 polycrystalline phase separated manganites were reported.
33 citations
TL;DR: In this paper, the Griffith's phase is inferred due to magnetic frustration with increasing Ti concentration in La0.4Bi0.6Mn1−xTixO3 around TC.
Abstract: Samples of La0.4Bi0.6Mn1−xTixO3 have been prepared and their microstructure, composition, and magnetic properties have been investigated for x = 0.05, 0.1, and 0.5.The deviation in the inverse susceptibility behavior from Curie-Weiss law and increase in susceptibility exponent indicates the evolution of the Griffith's phase in La0.4Bi0.6Mn1−xTixO3 around TC. The presence of Griffith's Phase is inferred due to magnetic frustration with increasing Ti concentration. The deviation between field cooled and zero field cooled magnetization curves is observed in these samples and is attributed to the appearance of the spin glass or cluster glass state that arises due to the magnetic anisotropy.
29 citations
TL;DR: A comprehensive study of actinide cation paramagnetism in acidic aqueous solution has been completed in perchlorate media using the Evans method, and the 5f electron behavior is compared to the 4f analogues.
Abstract: A comprehensive study of actinide cation paramagnetism in acidic aqueous solution has been completed in perchlorate media. Employing the Evans method, all the readily accessible actinide cations have been studied using our specially outfitted NMR spectrometer equipped for use with radioactive samples. The effective magnetic moments observed, ranging from 0 to 13 μB, differ from the isoelectronic lanthanides, previous solid actinide studies, and older solution studies. Actinide (IV) and (V) ions show less paramagnetic character, while some actinide (III) ions exhibit greater paramagnetic behavior than predicted from free-ion calculation. Temperature dependence of actinide magnetic susceptibilities from 5 to 80 °C are in good agreement with a Curie-like law except for U(VI), which appears to be temperature-independent. Diamagnetic behavior of Th(IV) exhibits a very low temperature dependence of the magnetic susceptibility. Some explanations for the observations are offered, and the 5f electron behavior is c...
27 citations
TL;DR: In this article, the Glauber dynamics for a bi-populated Curie-Weiss model was analyzed and the limiting behavior of the empirical averages in the limit of infinitely many particles was obtained.
Abstract: We analyze the Glauber dynamics for a bi-populated Curie-Weiss model. We obtain the limiting behavior of the empirical averages in the limit of infinitely many particles. We then characterize the phase space of the model in absence of magnetic field and we show that several phase transitions in the inter-groups interaction strength occur.
27 citations
TL;DR: In this paper, the intrinsic magnetic properties of (Fe 1-xCo x) 2B alloys have been studied on single crystals and temperature dependence of both magnetocrystalline anisotropy constant K 1 and spontaneous magnetization M s has been determined from magnetization isotherms measured between 10 and 1000 K.
Abstract: Intrinsic magnetic properties of (Fe 1-xCo x) 2B (x = 020, 025, 030, 035) alloys have been studied on single crystals Temperature dependence of both magnetocrystalline anisotropy constant K 1 and spontaneous magnetization M s has been determined from magnetization isotherms measured between 10 and 1000 K The highest anisotropy constant K 1 was obtained at x = 025, K 1 = 494 kJ/m 3 at T = 10 K The Curie temperature decreased from 966 to 930 K as x increased from 02 to 035
26 citations
TL;DR: In this paper, the magnetic properties of α-CoV2O6 were investigated by means of magnetic and heat capacity measurements, and the model of one-spin flip transition for a two-sublattice antiferromagnet was proposed.
21 citations
TL;DR: In this article, a three-sublattice model is used to elucidate anomalous behavior as, Neels two - sublattices model fails to explain increase in Curie temperature, even after the replacement of Co 2+ ions (3 µB) by Ni 2 + ions (2µB).
21 citations
TL;DR: In this article, the authors measured the change of the magnetic susceptibility of a thin gadolinium plates, cooled by water-flow at a temperature below the Curie point (TC=292 K), and found that the relaxation time of the magnetometer in the temperature range from 289.9 to 291.3 K can be approximated using the Landau-Khalatnikov equation with a kinetic coefficient value of 3.9×10-8 cm3/(erg×s).
Abstract: An experimental method is suggested for the determination of the rate of magnetic phase transitions. The method is based on the measurement of the change of magnetic susceptibility of a ferromagnetic sample in the vicinity of the phase transition in response to an abrupt change of the sample temperature. This paper describes the measurement of the change of the magnetic susceptibility of a thin gadolinium plates, cooled by water-flow at a temperature below the Curie point (TC=292 K). It was found that the relaxation time of the magnetic susceptibility of gadolinium in the temperature range from 289.9 to 291.3 K can be approximated using the Landau-Khalatnikov equation with a kinetic coefficient value γ = 3.9×10-8 cm3/(erg×s). The linear approximation does not fit well in the range from 291.3 to 293.2 K. The fundamental restriction of specific power of the magnetocaloric refrigerator (made by gadolinium plates) was estimated.
TL;DR: In this article, the concentration change in an initially homogeneous paramagnetic solution is studied interferometrically upon applying sufficiently strong inhomogeneous magnetic fields, and clear evidence is provided that an enrichment of paramagnetic ions occurs in the field gradient.
Abstract: © 1965-2012 IEEE. The concentration change in an initially homogeneous paramagnetic solution is studied interferometrically upon applying sufficiently strong inhomogeneous magnetic fields. For this purpose, five different magnetic field configurations are analyzed. Clear evidence is provided that an enrichment of paramagnetic ions occurs in the field gradient. In particular, we show that the shape of this enrichment layer maps the spatial distribution of the magnetic field gradient force.
TL;DR: In this article, lattice parameters, spontaneous magnetization, and the Curie temperature of MnAlGe and MnGaGe compounds with the Cu-Sb-type structure and their substituted compounds were investigated.
Abstract: Structure, lattice parameters, spontaneous magnetization (I
s
), and the Curie temperature (T
C
) of MnAlGe and MnGaGe compounds with the Cu
2
Sb-type structure and their substituted compounds were investigated. Cr substitution for Mn enhanced I
s
and T
C
, whereas Fe substitution for Mn degraded them. These behaviors are in accord with the previously reported results, and are also common to the MnGaGe compound series. For MnAlGe, lattice parameter a increases by 0.2% and 0.4% for Cr and Fe substitution, while c changes by +0.1% and -1.3%, respectively. For MnGaGe, a decreases by 0.08% for Cr and increases by 0.2% for Fe substitution, while c changes by +0.5% and -1.0%, respectively. T
C
tended to increase with increasing length of c, suggesting that the interlayer distance between Mn layers is a key factor related to the height of T
C
, i.e., the strength of the magnetic exchange interaction.
TL;DR: In this article, structural, electrical, and magnetic properties of bulk Cd1−xMnxGeAs2 crystals with low Mn content, x, varying from 0 to 0.037, were studied.
Abstract: We present the studies of structural, electrical, and magnetic properties of bulk Cd1−xMnxGeAs2 crystals with low Mn content, x, varying from 0 to 0.037. The studied samples have excellent crystallographic quality indicated by the presence of diffraction patterns never before observed experimentally for this compound. The electrical transport in our samples is dominated by thermal activation of conducting holes from the impurity states to the valence band with activation energy of about 200 meV. The defect states acting as ionic scattering centers with concentration in the range from 6 to 15 × 1017 cm−3 are observed. The effective Mn content in our samples, x¯θ, determined from fit of the susceptibility data to the Curie-Weiss law, is very close to the average chemical content, x. It indicates that the Mn ions are distributed randomly, substituting the Cd sites in the host CdGeAs2 lattice. We observe a negative Curie-Weiss temperature, |θ|≤3.1 K, increasing as a function of x. This indicates the significa...
TL;DR: In this paper, a mean-field modification of the classical Brillouin magnetization theory was proposed to explain the persistence of the spontaneous magnetization beyond the conventional Curie temperature.
Abstract: A positive-feedback mean-field modification of the classical Brillouin magnetization theory provides an explanation of the apparent persistence of the spontaneous magnetization beyond the conventional Curie temperature—the little understood “tail” phenomenon that occurs in many ferromagnetic materials. The classical theory is unable to resolve this apparent anomaly. The modified theory incorporates the temperature-dependent quantum-scale hysteretic and mesoscopic domain-scale anhysteretic magnetization processes and includes the effects of demagnetizing and exchange fields. It is found that the thermal behavior of the reversible and irreversible segments of the hysteresis loops, as predicted by the theory, is a key to the presence or absence of the “tails.” The theory, which permits arbitrary values of the quantum spin number J, generally provides a quantitative agreement with the thermal variations of both the spontaneous magnetization and the shape of the hysteresis loop.
TL;DR: In this paper, the Curie-Weiss constant was used to investigate the first order ferroelectric transition in filled tungsten bronze ceramics, and three categories were suggested: displacement-type, first-order, and displacement type.
Abstract: Ferroelectric transitions in filled tungsten bronze ceramics Sr4R2Ti4Nb6O30, Sr5RTi3Nb7O30 (R=La, Nb, Sm & Eu) and Ba4Nd2Ti4Nb6O30 are investigated with differential scanning calorimetry (DSC) and the Curie—Weiss law fitting to the dielectric constant. The magnitude of the Curie-Weiss constant C ~ 105 suggests displacement-type ferroelectric transition in the present compounds. The large ΔT difference between dielectric maximum temperature Tm and Curie—Weiss temperature T0) values indicate the difficult formation of ferroelectric domains or polar nanoregions in the present compounds and also the characteristics of the first order ferroelectric transition. Three categories are suggested for the ferroelectric transition in the above tungsten bronzes. The ferroelectric transition exhibits large thermal hysteresis. According to the DSC results, gradual recovery of the endothermic peak occurs after aging at temperature below the Curie point, indicating the gradual stability of the ferroelectric phase after cooling from the high-temperature para-electric phase. The relationship between the Curie—Weiss law fitting parameters and the nature of the ferroelectric transition is modified for the filled tungsten bronzes.
TL;DR: In this paper, the magnetic field dependence of the magnetic entropy change is used to determine the critical exponents β, γ, and δ, which are found to be β β 0.495, β γ 0.083, and β δ 0.18.
Abstract: The La0.8Na0.1MnO3 oxide was prepared by the solid-state reaction and annealed in air. The X-ray diffraction data reveal that the sample is crystallized in a rhombohedral structure with R3¯c space group. Magnetic study shows a second-order magnetic phase transition from ferromagnetic to paramagnetic state at the Curie temperature TC = 295 K. In addition, the magnetizations as a function of temperature and the magnetic field is used to evaluate the magnetic entropy change ΔSM. Then, we have deduced that the La0.8Na0.1MnO3 oxide has a large magnetocaloric effect at room temperature. Such effect is given by the maximum of the magnetic entropy change ΔSMmax = 5.56, and by the Relative cooling power (RCP) factor which is equal to 235 under a magnetic field of 5 T. Moreover, the magnetic field dependence of the magnetic entropy change is used to determine the critical exponents β, γ, and δ which are found to be β = 0.495, γ = 1.083, and δ = 3.18. These values are consistent with the prediction of the mean field...
TL;DR: In this article, a bipartite generalization of the Curie-Weiss model in a critical regime was considered and the change of variables that diagonalizes the Hessian matrix of the pressure functional associated to the model was studied.
Abstract: We consider a bipartite generalization of the Curie–Weiss model in a critical regime. In order to study the asymptotic behavior of the random vector of the total magnetization we apply the change of variables that diagonalizes the Hessian matrix of the pressure functional associated to the model. We obtain a new vector that, suitably rescaled, weakly converges to the product of a Gaussian distribution and a distribution proportional to \(\exp (-\xi x^{4})\), where the positive constant \(\xi \) can be computed from the pressure functional.
TL;DR: In this paper, the magnetic behavior of (Bi0.5Na 0.5)O3 has been investigated by DC magnetization and AC susceptibility techniques, showing that the interaction between magnetic moments is antiferromagnetic.
Abstract: (Bi0.5Na0.5)(Mn0.5Nb0.5)O3 has been sintered by hot-sintering method at ambient air. Composition has been checked with use of a scanning microscope. Magnetic behavior of (Bi0.5Na0.5)(Mn0.5Nb0.5)O3 has been investigated by DC magnetization and AC susceptibility techniques. (Bi0.5Na0.5)(Mn0.5Nb0.5)O3 exhibits a magnetic phase transition at 6.8 K. Below this temperature, the interaction between magnetic moments is antiferromagnetic. The resultant non-zero magnetic moment emerges because of weak precipitation of manganese oxide with ordering temperature at T ≈ 40 K. From the fit of the Curie–Weiss law to the AC susceptibility, the Weiss temperature θ = –2.3 K has been determined and Curie constant C = 1.15 emu K/molMn, close to the value expected for spin S = 2 of Mn3+, has been estimated. The antiferromagnetic state with spin-glass type features has been deduced. Crystal structures and partial density of states (DOS) have been simulated by ab initio method. DOS simulations showed half-metal electronic struct...
TL;DR: In this paper, Whangbo et al. show that magnetic properties of a system containing magnetic ions are related to its electronic structure, and that the Curie-Weiss temperature is related to the electronic structure of the system.
Abstract: E-mail: mike_whangbo@ncsu.eduReceived January 18, 2014, Accepted February 5, 2014Key Words : Nonequivalent magnetic ions, Curie-Weiss temperature, Mean field theory, Spin exchange pa-rameters, Density functional theory Magnetic properties of a system containing magnetic ionsare related to its electronic structure,
TL;DR: In this article, the distribution function of effective fields acting on magnetic atoms has been analyzed and the Curie temperatures, magnetizations of two magnetic sublattices, threshold concentrations of magnetic atoms, and magnetic phase diagrams of alloys have been calculated.
Abstract: Disordered alloys of magnetic atoms of two types have been considered within the Ising model based on the calculation and analysis of the distribution function of effective fields acting on magnetic atoms. The Curie temperatures, magnetizations of two magnetic “sublattices,” threshold concentrations of magnetic atoms, and magnetic phase diagrams of alloys have been calculated.
TL;DR: Thermal strain, permeability, and magnetization measurements of the ferromagnetic shape memory alloys Ni50+xMn27−xGa23 showed good linear relation behavior around the Curie temperature, in agreement with the theory by Takahashi, concerning itinerant electron ferromagnets.
Abstract: Thermal strain, permeability, and magnetization measurements of the ferromagnetic shape memory alloys Ni50+xMn27−xGa23 (x = 2.0, 2.5, 2.7) were performed. For x = 2.7, in which the martensite transition and the ferromagnetic transition occur at the same temperature, the martensite transition starting temperature TMs shift in magnetic fields around a zero magnetic field was estimated to be dTMs/dB = 1.1 ± 0.2 K/T, thus indicating that magnetic fields influences martensite transition. We discussed the itinerant electron magnetism of x = 2.0 and 2.5. As for x = 2.5, the M4 vs. B/M plot crosses the origin of the coordinate axis at the Curie temperature, and the plot indicates a good linear relation behavior around the Curie temperature. The result is in agreement with the theory by Takahashi, concerning itinerant electron ferromagnets.
TL;DR: In this paper, the structural and magnetic properties of alloys were investigated, and the magnetic isotherms were fitted to modified Langevin equation which indicated the presence of clusters with large magnetic moment.
Abstract: We investigated the structural and magnetic properties of Cu
2
Mn
1-x
Fe
x
Al (x = 0.25, 0.5, 0.75) alloys. Among the three compositions, only x = 0.25 composition crystallizes in single phase with L2
1
structure but its magnetic response indicates a complex magnetic structure. The magnetic isotherms were fitted to modified Langevin equation which indicates the presence of clusters with large magnetic moment. The ac susceptibility studies showed the presence of a superparamagnetic phase in the system over and above ferromagnetic order. To determine the nature of the interactions among the clusters, the variation of freezing temperature (T
f
) with applied ac frequency was analyzed using different models (Neel-Arrhenius, Vogel-Fulcher, and critical slowing down model).
TL;DR: In this paper, structural, electrical and magnetic properties of Fe doped La 0.33 Sr 0.67 MnO 3 manganites synthesized through solid-state reaction-route were systematically investigated.
TL;DR: In this paper, a physics-based phenomenological model of magnetization was proposed, in which magnetization is represented by the volumetric amounts of ferromagnetism (described by the extended Jiles-Atherton theory) and paramagnetisms (defined by the Curie-Weiss law) in respective phases.
Abstract: First order phase transitions may occur in several magnetic systems, with two structural phases having different magnetic properties each and a structural transition between them. Here, a novel physics based phenomenological model of such systems is proposed, in which magnetization is represented by the volumetric amounts of ferromagnetism (described by extended Jiles-Atherton theory) and paramagnetism (described by the Curie-Weiss law) in respective phases. An identification procedure to extract material parameters from experimental data is proposed. The proposed phenomenological approach was successfully applied to magnetocaloric Gd5(SixGe1−x)4 system and also has the potential to describe the behavior of Griffiths phase magnetic systems.
TL;DR: In this paper, the magnetic properties of magnetic fields with flux density up to 5 T and in high hydrostatic pressure up to 0.9 GPa were investigated in magnetic fields.
Abstract: Electrical resistance R, heat capacity C, ac susceptibility, and magnetic moment of orthorhombic La
0.85
Ag
0.15
MnO
3
ceramic were investigated in magnetic fields with flux density up to 5 T and in high hydrostatic pressures up to 0.9 GPa. Sharp lambda-like anomalies in R(T) and C(T) indicate ferromagnetic (FM)-paramagnetic transition. Magnetic field shifts these anomalies to higher temperature and smears them out confirming FM origin of the ordering. Magneto-resistance is negative and large reaching maximal value of about 70% for field with flux density of 5 T at the magnetic phase transition. The magnetic phase transition is accompanied with anomalies at 219.5 K in χ'(T) and at 221 K in χ"(T). The Curie temperature T
C
increases with applied pressure with the rate dT
C
/dp = 14.2 K/GPa. Magnetocaloric effect was evaluated from the magnetic entropy change ΔS, which was determined independently from heat capacity and magnetic moment measurements. The maximal values were obtained for μ
0
AH = 5 T and both values -ΔS = 5.85 Jkg
-1
K
-1
(heat capacity) and -ΔS = 5.80 Jkg
-1
K
-1
(magnetic moment) are comparable. Hydrostatic pressure of 0.84 GPa leads to an enhancement of -ΔS approximately about 14%.
08 Dec 2014
TL;DR: In this paper, the authors performed continuous-wave (cw) nuclear magnetic resonance measurements for 3He confined in 2.8-nm channel of FSM16 and showed that the magnetization shows a reduction from the Curie law at low temperature for the high areal density where 3 He in the channel consists of three portions; a solid first-layer, an amorphous-solid overlayer, and a fluid inside.
Abstract: We have performed continuous-wave (cw) nuclear magnetic resonance measurements for 3He confined in 2.8-nm channel of FSM16. The magnetization shows a reduction from the Curie law at low temperature for the high areal density where 3 He in the channel consists of three portions; a solid first-layer, an amorphous-solid overlayer, and a fluid inside. By an analysis for the magnetization and the available heat capacity data, the reduction can be attributed to an interaction of spins in amorphous solid and a degenerate of fluid.
TL;DR: In this article, the authors measured local susceptibility and spin relaxation rate of 54Fe nuclei implanted in III-V and II-VI semiconductors, including CdTe, CdSe, and InSb.
Abstract: Employing the time differential perturbed angular distribution method, we have measured local susceptibility and spin relaxation rate of 54Fe nuclei implanted in III-V and II-VI semiconductors, CdTe, CdSe, and InSb. The magnetic response of Fe, identified to occupy the metal as well as the semi-metal atom sites, exhibit Curie-Weiss type susceptibility and Korringa like spin relaxation rate, revealing the existence of localized moments with small spin fluctuation temperature. The experimental results are supported by first principle electronic structure calculations performed within the frame work of density functional theory.
TL;DR: In this article, the magnetization curves measured at 2.K showed no hysteresis neither remanence for all samples for all co-doped ZnO and Al polycrystalline powders.
TL;DR: In this article, the magnetic properties of a set of LaFe13−x−yCoySix compounds were investigated using magnetic measurements, thermal expansion, 57Fe Mossbauer spectroscopy and high resolution neutron powder diffraction methods over the temperature range 10-300 K.
Abstract: The magnetic properties of a set of LaFe13−x−yCoySix compounds (x = 1.6 − 2.6; y = 0, y = 1.0) have been investigated using magnetic measurements, thermal expansion, 57Fe Mossbauer spectroscopy and high resolution neutron powder diffraction methods over the temperature range 10–300 K. The natures of the magnetic transitions in these LaFe13−x−yCoySix compounds have been determined. The Curie temperatures of LaFe13−xSix were found to increase with Si content from TC = 219(5) K for Si content x = 1.6 to TC = 250(5) K for x = 2.6. Substitution of Co for Fe in LaFe10.4Si2.6 resulted in a further enhancement of the magnetic ordering temperature to TC = 281(5) K for the LaFe9.4CoSi2.6 compound. The nature of the magnetic transition at the Curie temperature changes from first order for LaFe11.4Si1.6 to second order for LaFe10.4Si2.6 and LaFe9.4CoSi2.6. The temperature dependences of the mean magnetic hyperfine field values lead to TC values in good agreement with analyses of the magnetic measurements. The magnetic entropy change, −ΔSM, has been determined from the magnetization curves as functions of temperature and magnetic field (ΔB = 0 − 5 T) by applying the standard Maxwell relation. In the case of LaFe12.4Si1.6 for example, the magnetic entropy change around TC is determined to be -ΔSM ∼ 14.5 J kg−1 K−1 for a magnetic field change Δ B = 0 − 5 T.