Showing papers on "Curie–Weiss law published in 2007"
TL;DR: In this article, the electronic, magnetic, and structural properties of the binary compound Mn3Ga were investigated and it was found that the material is hard magnetic with an energy product of Hc×Br=52.5kJm−3 and an average saturation magnetization of about 0.25μB∕at at 5K.
Abstract: This work reports about the electronic, magnetic, and structural properties of the binary compound Mn3Ga. The tetragonal DO22 phase of Mn3Ga was successfully synthesized and investigated. It has been found that the material is hard magnetic with an energy product of Hc×Br=52.5kJm−3 and an average saturation magnetization of about 0.25μB∕at. at 5K. The saturation magnetization indicates a ferrimagnetic order with partially compensating moments at the Mn atoms on crystallographically different sites. The Curie temperature is above 730K where the onset of decomposition is observed. The electronic structure calculations indicate a nearly half-metallic ferrimagnetic order with 88% spin polarization at the Fermi energy.
338 citations
TL;DR: In this paper, an osmium-based double perovskite with a Curie temperature of 725 K has been synthesized for spintronic materials with high spin polarization at room temperature.
Abstract: In the search for new spintronic materials with high spin polarization at room temperature, we have synthesized an osmium-based double perovskite with a Curie temperature of 725 K. Our combined exp ...
176 citations
TL;DR: In this article, a theoretical study of the magnetism induced in transition metal dioxides ZrO2 and TiO2 by substitution of the cation by a vacancy or an impurity from the groups 1A or 2A of the periodic table, where the impurity is either K or Ca.
Abstract: We perform a theoretical study of the magnetism induced in transition metal dioxides ZrO2 and TiO2 by substitution of the cation by a vacancy or an impurity from the groups 1A or 2A of the periodic table, where the impurity is either K or Ca. In the present study both supercell and embedded cluster methods are used. It is demonstrated that the vacancy and the K-impurity leads to a robust induced magnetic moment on the surrounding O-atoms for both the cubic ZrO2 and rutile TiO2 host crystals. On the other hand it is shown that Ca-impurity leads to a non magnetic state. The native O-vacancy does not induce a magnetic moment in the host dioxide crystal.
145 citations
TL;DR: In this article, the specific magnetization, the dynamic magnetic susceptibility, and the heat capacity of anion-deficient manganite were investigated, and it was shown that the ferromagnetic matrix of the material under study is characterized by a scatter in the exchange interaction intensities.
Abstract: For La
0.825
3+
Sr
0.175
2
+Mn3+O
2.912
2−
anion-deficient manganite, the specific magnetization, the dynamic magnetic susceptibility, and the heat capacity are investigated. This material is found to be an inhomogeneous ferromagnet below the Curie point T
C
≈ 122 K, which is much lower than the Curie point determined for the stoichiometric composition (T
C
≈ 268 K). An increase in magnetic field by two orders of magnitude leads to an increase in the Curie temperature by ΔT ≈ 12 K. The presence of oxygen vacancies leads to the frustration of a part, namely, V
fr ≈ 22%, of the indirect Mn3+-O-Mn3+ exchange interactions, but the spin glass state is not realized. The ferromagnetic matrix of the material under study is characterized by a scatter in the exchange interaction intensities. The heat capacity is found to exhibit an anomalous behavior. Based on the Banerjee magnetic criterion, it is established that the ferromagnet-paramagnet transition observed for La
0.825
3+
Sr
0.175
2+
Mn3+O
2.912
2−
anion-deficient manganite is a second-order thermodynamic phase transition. The mechanism and origin of the critical behavior of the system under investigation are discussed.
117 citations
TL;DR: In this article, the authors have bombarded graphite samples with protons at low temperatures and low fluences to attenuate the large thermal annealing produced during irradiation.
Abstract: We have bombarded graphite samples with protons at low temperatures and low fluences to attenuate the large thermal annealing produced during irradiation. The overall optimization of sample handling allowed us to find Curie temperatures ${T}_{c}\ensuremath{\gtrsim}350\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ at the fluences used. The magnetization versus temperature shows unequivocally a linear dependence, which can be interpreted as due to excitations of spin waves in a two-dimensional Heisenberg model with a weak uniaxial anisotropy.
110 citations
TL;DR: In this article, the influence of different compositional modifications on the magnetic entropy change and refrigerant capacity of Finemet, Nanoperm, HiTperm, and bulk amorphous alloys is presented.
Abstract: The influence of different compositional modifications on the magnetic entropy change and refrigerant capacity of Finemet, Nanoperm, HiTperm, and bulk amorphous alloys is presented. For all the studied alloys, the field dependence of the magnetic entropy change exhibits a quadratic dependence in the paramagnetic regime, a linear dependence in the ferromagnetic temperature range, and a potential law with a field exponent ∼0.75 at the Curie temperature. This exponent can be explained using the critical exponents of the Curie transition. It is shown that for alloys of similar compositional series, the magnetic entropy change follows a master curve behavior.
86 citations
TL;DR: Physical properties of the conductive oxide PdCoO 2 in the layered delafossite structure through measurements of the electrical resistivity, specific heat, magnetic susceptibility, polari....
Abstract: We report physical properties of the conductive oxide PdCoO 2 in the layered delafossite structure through measurements of the electrical resistivity, specific heat, magnetic susceptibility, polari...
79 citations
TL;DR: In this article, the spin-Hamiltonian parameters (g and A) and the molecular orbital coefficients ($β_2^{*2} $ and k) have been evaluated on vanadyl ions doped in polyvinyl alcohol (PVA) films.
Abstract: Electron paramagnetic resonance (EPR), optical, infrared and Raman spectral studies have been carried out on vanadyl ions doped in polyvinylalcohol (PVA) films. The spin-Hamiltonian parameters (g and A) and the molecular orbital coefficients ($\beta_2^{*2} $ and k) have been evaluated. The values of spin-Hamiltonian parameters confirm that the vanadyl ions are present in PVA films as $VO^{2+}$ molecular ions in an octahedral site with a tetragonal compression $(C_{4V})$. The temperature variation EPR studies reveal that the variation of number of spins with temperature is in accordance with Boltzmann law. It is interesting to observe that the variation of susceptibility with temperature obeys Curie–Weiss law. The FT-IR and FT-Raman spectrum exhibits few bands, which are attributed to O–H, C–H, CQC and C–O groups of stretching and bending vibrations. The optical absorption spectrum exhibits two bands, which are assigned to $^2B_{2g}\rightarrow ^2B_{1g}$ and $^2B_{2g}\rightarrow ^2E_g$ transitions in the decreasing order of energy.
76 citations
72 citations
TL;DR: In this article, a series of W-type hexagonal ferrites with the composition BaCoZn 1− x Mg x Fe 16 O 27 (0⩽ x ⩽0.6) were prepared by the conventional ceramic method to study their structural and magnetic properties as a function of temperature and composition.
63 citations
TL;DR: The discovery that a simply measured magnetic response is singular above the Curie temperature of a model, disordered magnet, and that the associated singularity grows to an anomalous divergence at TC is reported.
Abstract: Most physical and biological systems are disordered, even though the majority of theoretical models treat disorder as a weak perturbation. One particularly simple system is a ferromagnet approaching its Curie temperature, T_C, where all of the spins associated with partially filled atomic shells acquire parallel orientation. With the addition of disorder by way of chemical substitution, the Curie point is suppressed, but no qualitatively new phenomena appear in bulk measurements as long as the disorder is truly random on the atomic scale and not so large as to eliminate ferromagnetism entirely. Here we report the discovery that a simply measured magnetic response is singular above the Curie temperature of a model, disordered magnet, and that the associated singularity grows to an anomalous divergence at T_C. The origin of the singular response is the random internal field induced by an external magnetic field transverse to the favoured direction for magnetization. The fact that ferromagnets can be studied easily and with high precision using bulk susceptibility and a large variety of imaging tools will not only advance fundamental studies of the random field problem, but also suggests a mechanism for tuning the strength of domain wall pinning, the key to applications.
TL;DR: In this article, a cubic spinel structure with soft ferromagnetism and reversible magnetic entropy in CdCr2S4 was investigated by magnetization and heat capacity measurements, and the results suggest that sulfospinel probably is a promising candidate as working material in magnetic refrigeration technology.
Abstract: Magnetocaloric effect in CdCr2S4 was investigated by magnetization and heat capacity measurements CdCr2S4 is of a cubic spinel structure with soft ferromagnetism and performs reversible magnetic entropy in the whole experimental temperature range from 56to128K A large magnetic entropy change ∼704J∕kgK and adiabatic temperature change ΔTad∼26K are revealed for a field change of 0–5T near the Curie temperature of 87K These results suggest that sulfospinel probably is a promising candidate as working material in magnetic refrigeration technology
TL;DR: The double perovskites La2CoVO6, L2CoTiO6, and L2NiVO6 are described in this article, and the Curie-Weiss fits to the linear region of the 1/χ plots reveal Weiss temperatures of −107, −34.8, and 16.3
Journal Article•
TL;DR: In this paper, the saturation of magnetization was studied in pulsed magnetic fields for the triangular lattice antiferromagnet at temperatures below the magnetic ordering point, indicating a splitting of the field-induced transition to the paramagnetic phase.
Abstract: The saturation of magnetization was studied in pulsed magnetic fields $(H)$ for the triangular lattice antiferromagnet $\\mathrm{Rb}\\mathrm{Fe}{(\\mathrm{Mo}{\\mathrm{O}}_{4})}_{2}$ at temperatures $(T)$ below the magnetic ordering point ${T}_{N}$. The field-driven transition from the antiferromagnetic to the paramagnetic phase was studied by specific-heat measurements in a steady magnetic field. The specific heat shows a sharp peak at a value of the magnetic field below which a singularity in the magnetization curve occurs, indicating a splitting of the field-induced transition to the paramagnetic phase. This splitting vanishes at low temperatures. A complete $T\\text{\\ensuremath{-}}H$ phase diagram is derived experimentally both for the magnetic field lying in the spin plane and perpendicular to the plane. A spin-flip magnetic-resonance mode with the softening of the spin-wave spectrum at the saturation field has been observed. The gap of the spin-wave spectrum was found to be reduced by zero-point fluctuations by a factor of $0.82\\ifmmode\\pm\\else\\textpm\\fi{}0.08$ with respect to the prediction of the molecular-field theory.
TL;DR: In this article, a simplified model was developed to describe the Curie temperature suppression of ferromagnetic nanoparticles based on a size and shape dependent model of cohesive energy, and the critical temperature variations of the Ferromagnetic particles were deduced.
TL;DR: In this paper, the authors consider the superfluid-insulator transition for cold bosons under an effective magnetic field and investigate how the applied magnetic field affects the Mott transition within mean-field theory.
Abstract: We consider the superfluid-insulator transition for cold bosons under an effective magnetic field. We investigate how the applied magnetic field affects the Mott transition within mean-field theory and find that the critical hopping strength ${(t∕U)}_{c}$ increases with the applied field. The increase in the critical hopping follows the bandwidth of the Hofstadter butterfly at the given value of the magnetic field. We also calculate the magnetization and superfluid density within mean-field theory.
TL;DR: In this article, the temperature and magnetic field dependences of magnetocaloric effect (adiabatic temperature change Δ T ) were measured in single crystalline and polycrystalline Gd near the Curie point (T C ) using direct method with continuously changing magnetic field (H ) at different rates and the more conventional stepping of the magnetic field.
TL;DR: The magnetic properties of rare-earth ion paramagnetism have been investigated in this article, where it is shown that the magnetization of GdCoO3 and SmCoO 3 derives primarily from the rare earth ion paramagnetic properties.
Abstract: The temperature and magnetic field dependences of the static magnetization of the polycrystalline rare-earth cobaltites GdCoO3 and SmCoO3 have been measured It is shown that, below room temperature, the magnetization of both compounds derives primarily from the rare-earth ion paramagnetism The GdCoO3 and SmCoO3 compounds have been found to differ substantially in magnetic behavior, which can be traced to differences in their electronic shell structures The magnetic behavior of GdCoO3 is close to that of an array of free Gd3+ ions, whereas in SmCoO3 the deviation from the free-ion properties is very large because of the Sm3+ ground state being crystal-field split Van Vleck magnetic susceptibility measurements of SmCoO3 suggest that the splitting is ∼10 K
TL;DR: The magnetic field dependence of the magnetization of the isotropic ferromagnet Ni 2 MnGa has been measured close to the Curie temperature of 363.0 (0.4) K as mentioned in this paper.
TL;DR: In this article, the saturation magnetization of Mn0.57Ge0.43 films is high, up to 327emu∕cm3 (1.04μB∕Mn) at 5K, and the Curie temperature is about 213K.
Abstract: Homogeneous MnxGe1−x ferromagnetic semiconductor films with high Mn concentration were prepared, contrasting with dilute inhomogeneous MnxGe1−x magnetic semiconductors. The saturation magnetization of Mn0.57Ge0.43 films is high, up to 327emu∕cm3 (1.04μB∕Mn) at 5K, and the Curie temperature is about 213K. The Mn0.57Ge0.43 films show semiconducting resistance, but the magnetoresistance is negligibly small. The anomalous Hall effect was observed below the Curie temperature, which is consistent with the magnetic measurements. The global ferromagnetism was discussed based on s,p-d exchange coupling between the weakly localized s,p hole carriers and the strongly localized d electrons of the Mn atoms.
TL;DR: In this paper, the fabrication and magnetic characterization of a number of Co−Fe-Ni-Si-B and Co-Fe-Cr-Si−B microwires with total diameter between 15 and 37μm fabricated by the Taylor-Ulitovsky method with low Curie temperature possessing also good magnetic softness and high GMI effect.
Abstract: A novel family of magnetic materials, thin ferromagnetic metallic glass-coated wires (1/30 μm in diameter) produced by the Taylor–Ulitovsky method present excellent magnetic properties such as magnetic bistability, GMI effect or enhanced magnetic softness attracting great attention for sensor applications. In this paper we report novel results on the fabrication and magnetic characterization of a number of Co–Fe–Ni–Si–B and Co–Fe–Cr–Si–B microwires with total diameter between 15 and 37 μm fabricated by the Taylor–Ulitovsky method with low Curie temperature possessing also good magnetic softness and high GMI effect. Magnetization, hysteresis loops, magnetic susceptibility and their magnetic field dependence and GMI effect at frequencies up to 500 MHz have been measured. Few samples possessing low T C (below 100 °C) also present high GMI effect with GMI ratio achieving 110% at 100 MHz. Additions of Ni or Cr to the conventional Co–Fe–Si–B composition with vanishing magnetostriction constant resulted in significant decreasing of the Curie temperature. Concrete applications have been designed such as the temperature sensors applications based on drastic change of the magnetic properties in the vicinity of Curie temperature.
TL;DR: In this article, the structure of Mn clusters in (Ga,Mn)N and the interactions of the magnetic Mn ions and clusters were studied using first-principles calculations.
Abstract: The structure of Mn clusters in (Ga,Mn)N and the interactions of the magnetic Mn ions and clusters are studied using first-principles calculations. Curie temperatures are calculated using mean-field and Monte Carlo methods. It is found that joining substitutional Mn ions to clusters is energetically favorable and especially the structures of two to four Mn ions formed around a single N ion are most stable. These clusters are always found to have a ferromagnetic ground state, and ferromagnetic intercluster interactions are also present even at relatively long distances. For randomly distributed Mn impurities, high Curie temperatures are obtained at high Mn concentrations (above room temperature for $x\ensuremath{\gtrsim}0.14$).
TL;DR: In this article, high-resolution transmission electron microscope (HRTEM) analysis revealed that Mn ions were substitutionally well incorporated into the crystal lattice of ZnO for all samples.
TL;DR: In this paper, the authors measured the high-field magnetization in high-quality samples made from Re-based double perovskites: A2FeReO6 (A2=Ca2, Sr2, BaSr), with Curie temperatures ranging from 360 up to 610K.
Abstract: Using static magnetic fields up to 30T, the authors have measured the high-field magnetization in high-quality samples made from Re-based double perovskites: A2FeReO6 (A2=Ca2, Sr2, BaSr) and Sr2CrReO6, with Curie temperatures ranging from 360 up to 610K. The results indicate that the saturation magnetization in these compounds is higher than the assumed spin-only ionic values, 3μB∕f.u. for A2FeReO6 and 1μB∕f.u. for Sr2CrReO6, which is explained by the large orbital contribution to the magnetization. Indirectly, these results show that Re-based double perovskites cannot be described as half-metals.
TL;DR: In this article, the magnetic properties near the magnetic transition in a polycrystalline sample of a manganite Tb0.9Sn0.1MnO3 were investigated.
Abstract: The magnetocaloric effect in magnetic materials is of great interest nowadays. In this article we present an investigation about the magnetic properties near the magnetic transition in a polycrystalline sample of a manganite Tb0.9Sn0.1MnO3. Particularly, we are interested in describing the nature of the magnetic interactions and the magnetocaloric effect in this compound. The temperature dependence of the magnetization was measured to determine the characteristics of the magnetic transition and the magnetic entropy change was calculated from magnetization curves at different temperatures. The magnetic solid is paramagnetic at high temperatures. We observe a dominant antiferromagnetic interaction below Tn=38 K for low applied magnetic fields; the presence of Sn doping in this compound decreases the Neel temperature of the pure TbMnO3 system. A drastic increase in the magnetization as a function of temperature near the magnetic transition suggests a strong magnetocaloric effect. We found a large magnetic en...
TL;DR: In this article, the magnetic field and temperature dependences of the adiabatic temperature change (Δ T ) were measured in single-crystalline and poly-crystal gadolinium (Gd) near the Curie point (T C ) by a direct method while continuously changing magnetic field (H ) at different rates and the more conventional stepping of the magnetic fields from 0 to 1.2
TL;DR: In this article, the magnetocaloric effect of Sr vacancies in La 0.7 Sr 0.3− x □ x MnO 3 compounds with x = 0 and 0.05 was investigated.
TL;DR: In this paper, the two different magnetically ordered phases of CeRhIn$5$ were determined by neutron diffraction, evidenced by bulk measurements under applied magnetic field in its basal plane.
Abstract: The magnetically ordered ground state of CeRhIn$_{5}$ at ambient pressure and zero magnetic field is an incomensurate helicoidal phase with the propagation vector $\bf{k}$=(1/2, 1/2, 0.298) and the magnetic moment in the basal plane of the tetragonal structure. We determined by neutron diffraction the two different magnetically ordered phases of CeRhIn$_{5}$ evidenced by bulk measurements under applied magnetic field in its basal plane. The low temperature high magnetic phase corresponds to a sine-wave structure of the magnetization being commensurate with $\bf{k}$=(1/2, 1/2, 1/4). At high temperature, the phase is incommensurate with $\bf{k}$=(1/2, 1/2, 0.298) and a possible small ellipticity. The propagation vector of this phase is the same as the one of the zero-field structure.
TL;DR: In this paper, a polycrystalline Ca 2 NiWO 6 double perovskite has been confirmed by X-ray powder diffraction (XRD) and the crystal structure is monoclinic, space group P2 1 /n, with a =5.4061(2)
Abstract: Polycrystalline Ca 2 NiWO 6 double perovskite has been prepared by solid-state reaction at 1150 °C. The crystal structure of this material has been confirmed by X-ray powder diffraction (XRD). At room temperature, the crystal structure is monoclinic, space group P2 1 /n, with a =5.4061(2) A, b =5.5389(2) A, c =7.6895(3) A, β =90.232(2)°. Magnetic susceptibility and electron spin resonance experiments on Ca 2 NiWO 6 show at high temperature a Curie–Weiss behavior with a θ =−75 K. From the Curie–Weiss behavior, the effective magnetic moment is 2.85 μ B , which is in agreement with the presence of Ni 2+ in the system. At low temperatures, below 52.5(0.2) K, the magnetic susceptibility shows antiferromagnetic behavior. From the experimental data and the mean field theory of antiferromagnetism we estimated the Ni interactions among the nearest Ni neighbors and the second nearest Ni neighbors.
TL;DR: In this paper, the authors investigated the magnetic and transport behaviors of Ge1−xMnxTe thin films with high Mn composition (x=0.98) grown by solid-source molecular-beam epitaxy.
Abstract: The authors investigate the magnetic and transport behaviors of Ge1−xMnxTe thin films with high Mn composition (x=0.98) grown by solid-source molecular-beam epitaxy. The temperature-dependent magnetization (M-T) gives a Curie paramagnetic temperature θp∼120K, in contrast to the Curie temperature of TC∼95K obtained from the Arrott plot and temperature-dependent resistivity measurement. The resistivity and M-T behaviors can be attributed to weak localization effect of disordering. The authors discussed the ferromagnetism in Ge0.02Mn0.98Te on the basis of the Ruderman-Kittel-Kasuya-Yoshida interaction and clustering effect.