Showing papers on "Curie–Weiss law published in 2002"
TL;DR: Analytical expressions for the Curie temperature and the magnetization in the limit of low carrier density are derived, obtaining excellent quantitative agreement with Monte Carlo simulation results and good qualitative agreement with experimental results.
Abstract: We theoretically study the development of spontaneous magnetization in diluted magnetic semiconductors as arising from a percolation of bound magnetic polarons. Within the framework of a generalized percolation theory we derive analytic expressions for the Curie temperature and the magnetization in the limit of low carrier density, obtaining excellent quantitative agreement with Monte Carlo simulation results and good qualitative agreement with experimental results.
634 citations
TL;DR: The magnetocaloric effect (MCE) originated from the itinerant-electron metamagnetic transition for La(FexSi1−x)13 compounds has been investigated as discussed by the authors.
Abstract: The magnetocaloric effect (MCE) originated from the itinerant-electron metamagnetic transition for La(FexSi1−x)13 compounds has been investigated. With increasing Fe concentration, the MCE is enhanced and both the isothermal magnetic entropy change ΔSm and the adiabatic temperature change ΔTad for the compound with x=0.90 are −28 J/kg K and 8.1 K, respectively, by changing the magnetic field from 0 to 2 T. Similar large MCE values are achieved around room temperature by controlling the Curie temperature by means of hydrogen absorption. Consequently, La(FexSi1−x)13 compounds are promising as magnetic refrigerant materials working in relatively low magnetic fields.
458 citations
TL;DR: In this paper, the temperature dependencies of electrical resistance and carrier concentration were measured to investigate the relation between the ferromagnetism and transport property, showing coexistence of ferromagnetic and paramagnetic phases.
Abstract: Mn-doped GaN films on sapphire (0001) substrates were grown by molecular beam epitaxy system using ammonia as nitrogen source. The result of magnetization measurement gives Curie temperature as high as 940 K. The field and temperature dependencies of the magnetization show coexistence of ferromagnetic and paramagnetic phases. In addition, the temperature dependencies of electrical resistance and carrier concentration were measured to investigate the relation between the ferromagnetism and transport property. Below about 10 K, a similar anomalous increase of magnetization and resistance is observed.
178 citations
TL;DR: It is shown that both light beam and bias voltage generate an isothermal and reversible crossover between the paramagnetic and ferromagnetic phases, in the way that is predetermined by the structure design.
Abstract: A strong influence of illumination and electric bias on the Curie temperature and saturation value of the magnetization is demonstrated for semiconductor structures containing a modulation-doped p-type ${\mathrm{Cd}}_{0.96}{\mathrm{Mn}}_{0.04}\mathrm{Te}$ quantum well placed in various built-in electric fields. It is shown that both light beam and bias voltage generate an isothermal and reversible crossover between the paramagnetic and ferromagnetic phases, in the way that is predetermined by the structure design. The observed behavior is in quantitative agreement with the expectations for systems, in which ferromagnetic interactions are mediated by the weakly disordered two-dimensional hole liquid.
173 citations
TL;DR: In this article, the mean field solution of the Ising model on a Barabasi-Albert scale-free network with ferromagnetic coupling between linked spins is presented and the critical temperature T c for the Ferromagnetic to paramagnetic phase transition (Curie temperature) is infinite and the effective critical temperature for a finite size system increases as the logarithm of the system size.
149 citations
TL;DR: In this article, it was suggested that hybridization contributes significantly to the hole binding energy of Mn acceptors in III-V compounds, leading in an extreme case to the formation of Zhang-Rice-like small magnetic polarons.
Abstract: It is suggested that $p\ensuremath{-}d$ hybridization contributes significantly to the hole binding energy ${E}_{b}$ of Mn acceptors in III-V compounds, leading in an extreme case to the formation of Zhang-Rice-like small magnetic polarons. The model explains both the strong increase of ${E}_{b}$ and the evolution of a Mn spin-resonance spectrum with the magnitude of valence-band offsets. The high Curie temperature above room temperature is shown to be in accordance with the mean-field Zener model.
86 citations
TL;DR: In this paper, the authors used supercell and frozen-magnon approaches to study the dependence of the magnetic interactions in (Ga,Mn)As on the Mn concentration.
Abstract: We use supercell and frozen-magnon approaches to study the dependence of the magnetic interactions in (Ga,Mn)As on the Mn concentration. We report the parameters of the exchange interaction between Mn spins and the estimates of the Curie temperature within the mean-field and random-phase approximations. In agreement with experiment we obtain a nonmonotonous dependence of the Curie temperature on the Mn concentration. We estimate the dependence of the Curie temperature on the concentration of the carries in the system and show that the decrease of the number of holes in the valence band leads to a fast decrease of the Curie temperature. We show that the hole states of the valence band are more efficient in mediating the exchange interaction between Mn spins than the electron states of the conduction band.
78 citations
TL;DR: In this paper, it was shown that the exchange parameters determined from the dispersion relations of the magnetic excitations should be reduced, which suggests the importance of the renormalization effect in the magnetization.
Abstract: ${\mathrm{KCuCl}}_{3}$ is a three-dimensional coupled spin-dimer system and has a singlet ground state with an excitation gap $\ensuremath{\Delta}{/k}_{\mathrm{B}}=31\mathrm{K}.$ High-field magnetization measurements for ${\mathrm{KCuCl}}_{3}$ have been performed in static magnetic fields of up to 30 T and in pulsed magnetic fields of up to 60 T. The entire magnetization curve including the saturation region was obtained at $T=1.3\mathrm{K}.$ From the analysis of the magnetization curve, it was found that the exchange parameters determined from the dispersion relations of the magnetic excitations should be reduced, which suggests the importance of the renormalization effect in the magnetic excitations. The field-induced magnetic ordering accompanied by the cusplike minimum of the magnetization was observed, as in the isomorphous compound ${\mathrm{TlCuCl}}_{3}.$ The phase boundary was almost independent of the field direction, and is represented by the power law. These results are consistent with the magnon Bose-Einstein condensation picture for field-induced magnetic ordering.
77 citations
TL;DR: A lattice spin-fermion model for diluted magnetic semiconductors (DMS) is investigated numerically, improving on previously used mean-field approximations and formal analogies between DMS and manganites are discussed.
Abstract: A lattice spin-fermion model for diluted magnetic semiconductors (DMS) is investigated numerically, improving on previously used mean-field approximations. Curie temperatures are obtained varying the Mn spin $x$ and hole $n$ densities, and the impurity-hole exchange $J$ in units of the hopping $t$. Optimal values are found in the subtle intermediate regime between itinerant and localized carriers. At intermediate and large $J/t$, a ``clustered'' state is observed above the Curie temperature and ferromagnetism is suppressed. Formal analogies between DMS and manganites are discussed.
69 citations
TL;DR: In this paper, a nonstoichiometric Ni53Mn25Ga22 alloy was found to undergo a reverse martensitic transformation from ferromagnetic martensite to paramagnetic austenite at a magnetic transition temperature (134°C) higher than the Curie temperature of the Ni2MnGa alloy (103°C).
Abstract: A co-occurrence of magnetic and structural transitions was observed in a nonstoichiometric Ni53Mn25Ga22 alloy which undergoes a reverse martensitic transformation from ferromagnetic martensite to paramagnetic austenite at a magnetic transition temperature (134 °C) higher than the Curie temperature of the stoichiometric Ni2MnGa alloy (103 °C). The effect of the magnetic field on the phase transition temperature was found to be two orders of magnitude greater in the present alloy than in Ni2MnGa due to the absence of the ferromagnetic state in austenite. This may open the possibility of utilizing NiMnGa alloys at a low magnetic field.
58 citations
TL;DR: In this paper, the dielectric properties of Barium strontium titanate (BST) were studied as a function of frequency and temperature and well-defined ferroelectric behavior of first order transition was observed.
Abstract: Here we report detailed dielectric studies carried out on a Barium strontium titanate (BST) (95:5) composition. The material was synthesized by conventional ceramic method and microwave processing, and the later technique resulted in material with high density, improved microstructure and dielectric properties. The dielectric properties were studied as a function of frequency and temperature and well-defined ferroelectric behavior of first order transition was observed. It follows Curie–Weiss law above transition temperature (paraelectric region). Curie temperature is slightly higher for microwave sintered (MS) material.
TL;DR: The oxide materials La3MO7, M=Ru and Os have been prepared, the Os phase for the first time, and they have been shown to exhibit Curie-Weiss paramagnetism at high temperatures with effective moments consistent with S= 3 2, as expected for the 4d3 and 5d3 electronic configurations associated with oxidation state +5, thus providing evidence for local moment magnetism.
TL;DR: In this paper, the soft magnetic response of nanocrystalline Fe 7 3.5 - x Co x Si 1 3. 5 B 9 Cu 1 Nb 3 (x=0, 30, and 45) samples are analyzed above room temperature through the temperature evolution of the magnetic permeability and the associated loss factor.
Abstract: The soft magnetic response of nanocrystalline Fe 7 3 . 5 - x Co x Si 1 3 . 5 B 9 Cu 1 Nb 3 (x=0, 30, and 45) samples are analyzed above room temperature through the temperature evolution of the magnetic permeability and the associated loss factor. Moreover, the actual structure and composition of the crystalline phase is analyzed through neutron-diffraction studies. The results show that the inclusion of Co atoms give rise to an improvement in the soft magnetic behavior at high temperatures with respect to the Fe-based sample as a consequence of the increase in the Curie temperature of the precipitated crystallites. However, the role of the residual amorphous matrix cannot be disregarded and the decrease in its Curie temperature for the Co richest sample gives rise to a deterioration of the high-temperature soft magnetic response. The observed temperature evolution is analyzed within the framework of the random anisotropy model and associated with the temperature dependence of the magnetic coupling between the ferromagnetic crystals.
TL;DR: Magnetic data for Ln MnO 3 (Ln =Ho, Er, Tm, Yb, and Lu) having the hexagonal crystal structure of P 6 3 cm were presented in this article.
TL;DR: In this paper, the effects of Mn substitution on the magnetic properties of Er2Fe17−xMnx compounds have been investigated by different experimental techniques, and an unusual composition dependence of the unit cell volume at room temperature occurs due to a strong magnetovolume effect, which has been confirmed by high temperature linear thermal expansion measurements.
Abstract: The effects of Mn substitution on the magnetic properties of Er2Fe17−xMnx compounds have been investigated by different experimental techniques. An unusual composition dependence of the unit cell volume at room temperature occurs due to a strong magnetovolume effect, which has been confirmed by high temperature linear thermal expansion measurements. From magnetization measurements the composition dependence of the spontaneous magnetization of the 3d-sublattice magnetic moment and of the Curie temperature has been determined. Spin reorientation has been detected for compounds with 3⩽x⩽5.5, as well as remarkable magnetic history effects.
TL;DR: In this article, the magnetic properties of the intermetallic phases RNi4B (R=Ce, Nd, Gd, Dy, and Gd and Dy) have been studied.
TL;DR: The crystal structures, electronic and magnetic properties of conducting molecular magnets developed in this article are reviewed and the one-to-one correspondence of the anomalies appearing on the magnetization curves with those on magnetoresistance supports the presence of the π-d interaction.
TL;DR: In this article, the magnetic properties of the compounds Gd5T3 (T=Si,Ge,Sn), as obtained from DC magnetisation measurements in applied fields up to 90 kOe and in a temperature range between 3 and 300 K.
TL;DR: In this paper, the Curie temperature of ferroelectric films is studied using spin-1/2 transverse Ising model with long-range interaction within the framework of the effective field theory.
Abstract: In this paper, the Curie temperature of ferroelectric films is studied using spin-1/2 transverse Ising model with long-range interaction within the framework of the effective-field theory. The dependence of the Curie temperature on the thickness of the film, the surface interaction and the transverse field were investigated. It is assumed that the long-range interaction decays with the distance between the pseudo-spins as a power law. The dependence of the Curie temperature and the critical transverse field on the long-range exponent are obtained.
TL;DR: The spin 1/2 Cu2+ ions in beta-Cu3V2O8 occupied the sites of a Kagome-staircase lattice, an anisotropic variant of the Kagome net: buckled layers and imbedded plaquettes of three edge shared CuO4 squares break the ideal Kagome symmetry as discussed by the authors.
Abstract: The spin-1/2 Cu2+ ions in beta-Cu3V2O8 occupy the sites of a Kagome-staircase lattice, an anisotropic variant of the Kagome net: buckled layers and imbedded plaquettes of three edge-shared CuO4 squares break the ideal Kagome symmetry. Susceptibility and heat capacity measurements show the onset of short-range ordering at approximately 75 K, and a magnetic phase transition with the characteristics of antiferromagnetism at ~29 K. Comparison to the Curie Weiss theta (theta,CW = -135 K) indicates that the geometric frustration is largely relieved by the anisotropy. A ferromagnetic contribution to the magnetization below the ordering temperature and negative magnetization in zero-field cooled measurements at low fields are attributed to uncompensated spins at grain boundaries or defects.
TL;DR: GdPdCd was obtained in pure form via reaction of the elements in a sealed tantalum tube in a high-frequency furnace as mentioned in this paper, and the structure was investigated by X-ray diffraction on both powders and single crystals.
TL;DR: In this paper, the magnetization as a function of temperature and magnetic field was measured for La 0.67 Ca 0.33 MnO 3, La 1.67 Ba 0.34 MnO 2, La 0, 1.33 Na 0.5 Na 1.5, La 2.67 Na 0, 0.3 Na 0., 0.4 Na 0, 0.1 Na 0.33, and 0.
TL;DR: In this article, a detailed analysis of the temperature dependence of magnetization data reveals: spin-wave excitations at low-temperature, single-particle excitations and local spin-density fluctuations (LSDF's) over a wide range of intermediate temperatures and enhanced fluctuations in the local magnetization for temperature close to T c contribute dominantly to the thermal demagnetization of spontaneous magnetizations.
Abstract: The magnetization as a function of field and temperature has been measured for a series of amorphous Fe 9 0 - x Mn x Zr 1 0 alloys with x=0-12 in the temperature range 4.2-300 K. All the samples of the present study show double transition (reentrant) behavior below room temperature. The high-temperature transition (T c ) decreases linearly at about 6 K/at. % of Mn, while the low-temperature transition (T s g ) increases at about 2.6 K/at. % of Mn. A detailed analysis of the temperature dependence of magnetization data reveals: (i) Spin-wave excitations at low-temperature, single-particle excitations and local-spin-density fluctuations (LSDF's) over a wide range of intermediate temperatures and enhanced fluctuations in the local magnetization for temperature close to T c contribute dominantly to the thermal demagnetization of spontaneous magnetizations; (ii) external applied magnetic field of strength ≥5 kOe suppresses the LSDF's; (iii) the spin-wave stiffness constant (D) decreases from 35.6′0.3 to 23.2′0.2 meV A 2 with increasing Mn concentration; and (iv) the D/T c ratio remains constant for all the compositions. A study of critical behavior of the magnetic order-disorder transition by various methods suggest that the critical exponents obtained below and above Curie temperature obey a scaling law [δ-1=γ/β and α+γ=2(1-β)] with a high degree of accuracy in the asymptotic critical region. The exponents are independent of composition and are in close agreement with the values those predicted for three-dimensional Heisenberg ferromagnets. The magnetic parameters such as high-field susceptibility, coercivity, local magnetic anisotropy, and spin-glass behavior, obtained from the low-temperature magnetization data, are consistent with the presence of a mixed magnetic state. The detailed analysis of high-field thermomagnetization data could be explained in terms of the nearest-neighbor Heisenberg model. Moreover, the temperature dependence of the magnetic behavior is discussed in terms of competing ferromagnetic and antiferromagnetic exchange interactions.
TL;DR: In this article, the effect of deuteration on the ferroelectric properties of glycine phosphite has been investigated and the reciprocal permittivity strictly fulfills the Curie-Weiss low in each paraelectric phase.
Abstract: In order to investigate the effect of deuteration on the ferroelectric properties of glycine phosphite, single crystals with various deuteration ratio x (0 ∼ 0.78) have been prepared. The crystal form is not affected by the deuteration. Internal bias fields influenced hysteresis loops in all samples cut from crystals. Temperature dependence of permittivity of all samples shows a dielectric anomaly characteristic of the second order ferroelectric phase transition. The reciprocal permittivity strictly fulfills the Curie-Weiss low in each paraelectric phase. The transition temperature T C increases with the ratio x from 224K ( x = 0) to 320K ( x = 0.78). The transition temperature of fully deuterated crystal ( x = 1) is roughly estimated to be about 350K. The Curie constant is slightly affected by the deuteration.
TL;DR: In this paper, structural and magnetic properties of the YCo4Al and PrCo 4Al intermetallic compounds were reported. But the properties of these compounds were not discussed.
TL;DR: The magnetic properties of the Dy12xCaxMnO3 solid solution (0 # x # 060) have been studied as a function of temperature and magnetic field as discussed by the authors.
TL;DR: In this article, temperature-dependent magnetic susceptibility measurements on single crystals indicate that EuSnP is an antiferromagnet with a Neel temperature of 21 K, consistent with the assignment of a 2+ valence to the Eu ions, seven unpaired electrons.
TL;DR: In this article, a model for the ferromagnetism of a Mott insulator Lu 2 V 2 O 7 is proposed, where substitution effects of Ti and Nb atoms for V atoms in Lu 2V 2 O7 have been studied, where all ions are found to have valence of +4.
TL;DR: The Eu2Si5N8 structure consists of a three-dimensional network of corner sharing SiN4 tetrahedra in which the europium ions occupy two crystallographically different sites as mentioned in this paper.
TL;DR: In this article, the properties of two new classes of highly p-type doped II-VI diluted magnetic semiconductors (DMS): thin layers of Be 1-x Mn x Te:N and bulk Zn 1 -x Mn X Te:P are presented, and a qualitative analysis of the results favours those models of the carrier-mediated ferromagnetism in DMS which allow for coupling of only a part of the available spins.
Abstract: Magnetic properties of two new classes of highly p-type doped II-VI diluted magnetic semiconductors (DMS): thin layers of Be 1-x Mn x Te:N and bulk Zn 1-x Mn x Te:P are presented. Despite the fact that the samples are insulating, we observe clear indications of the low temperature ferromagnetic correlation, namely: (i) positive Curie-Weiss temperature (T CW 2 K), and (ii) open hysteresis loops at temperatures below T CW . A qualitative analysis of the results favours those models of the carrier-mediated ferromagnetism in DMS which allow for the coupling of only a part of the available spins.