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Showing papers on "Curie–Weiss law published in 2003"


Journal ArticleDOI
TL;DR: Magnetic circular dichroism measurements showed a strong interaction between the sp carriers and localized d spins, indicating that Zn(1-x)Cr(x)Te is a diluted magnetic semiconductor.
Abstract: The magnetic and magneto-optical properties of a Cr-doped II-VI semiconductor ZnTe were investigated. Magnetic circular dichroism measurements showed a strong interaction between the sp carriers and localized d spins, indicating that Zn(1-x)Cr(x)Te is a diluted magnetic semiconductor. The Curie temperature of the film with x=0.20 was estimated to be 300+/-10 K, which is the highest value ever reported for a diluted magnetic semiconductor in which sp-d interactions were confirmed. In spite of its high Curie temperature, Zn(1-x)Cr(x)Te film shows semiconducting electrical transport properties.

390 citations


Journal ArticleDOI
TL;DR: In this article, a single crystal of MnSi2−x was obtained by a modified Czochralski pulling technique in a cold copper crucible, which revealed the sample to be Mn4Si7.

136 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of antisite (AS) defects and electron doping on the FM-PM transition of Sr 2 FeMoO 6 (SFMO) double perovskite has been studied.
Abstract: The effect of antisite (AS) defects and electron doping on the ferromagnetic-paramagnetic (FM-PM) transition of Sr 2 FeMoO 6 (SFMO) double perovskite has been studied. From a detailed analysis of the magnetization curves across the FM-PM transition we conclude that AS defects decrease the average strength of the magnetic interactions, although, remarkably enough, some of them are actually enhanced. It follows that the mean-field Curie temperature lowers whereas the onset of magnetization occurs at somewhat higher temperatures. The FM-PM transition has also been analyzed in electron-doped La x Sr 2 - x FeMoO 6 , where the AS defects concentration has been found to increase upon La doping. It turns out that in spite of the presence of AS, the mean-field Curie temperature significantly rises upon La and electron doping. This experimental finding contrasts with some recent predictions and emphasizes the role of itinerant electrons in the ferromagnetic coupling in these oxides. Moreover, our results indicate that disordered (i.e., with AS) double perovskite materials should be described as systems with random magnetic anisotropy.

136 citations


Journal ArticleDOI
TL;DR: Using density-functional theory in the local density approximation and spinfluctuation theory, the Curie temperatures of the zinc-blende half-metallic ferromagnets VAs, CrAs, MnAs, and the Heusler compound NiMnSb have been estimated, the lower bounds obtained being ab initio as mentioned in this paper.
Abstract: Using density-functional theory in the local-density approximation and spin-fluctuation theory, the Curie temperatures of the zinc-blende half-metallic ferromagnets VAs, CrAs, MnAs and the Heusler compound NiMnSb have been estimated, the lower bounds obtained being ab initio. The orders of magnitude are the same as the Curie temperature of the half-metallic ferromagnet NiMnSb with ${T}_{c}=701\mathrm{K}.$ Of the three compounds VAs, CrAs, and MnAs, the highest ${T}_{c}$ is calculated for CrAs, for which the Fermi energy is in the middle of the minority-spin electron gap; its Curie temperature might be as high as 1000 K. The Curie temperature drops sharply when the Fermi energy moves into the minority-electron conduction band as in the case of MnAs.

112 citations


Journal ArticleDOI
TL;DR: In this paper, the electro-optical properties of monoclinic Sn2P2S6 single crystals are measured by direct interferometric technique for electric fields applied parallel to the crystallographic x-axis that lies near the spontaneous polarization vector.

85 citations


Journal ArticleDOI
TL;DR: In this article, the electronic and magnetic structure of a doped α-hematite was investigated using density functional theory and it was shown that α-mathematite is an antiferromagnetic insulator with strong ferromagnetic coupling in the cation planes perpendicular to the c axis and antiferrous coupling between these planes.
Abstract: There has been much interest in doping traditional semiconductors such as GaAs with Mn or other transition metals in order to obtain semiconductors that are magnetic at room temperature. Some of the goals of this research have been a Curie temperature that exceeds 400 K and the possibility of both n- and p-type doping. An alternative approach is to investigate nontraditional semiconducting materials that are known to be magnetic at room temperature. An example of such a material is solid solutions of the minerals ilmenite (FeTiO3) and α-hematite (Fe2O3). In this article we investigate the electronic and magnetic structure of Ti doped α-hematite using density functional theory and find within this model: α-hematite is an antiferromagnetic insulator with strong ferromagnetic coupling in the cation planes perpendicular to the c axis and antiferromagnetic coupling between these planes. Substitution of Ti for Fe produces a net moment of 4μB and a negative carrier in one spin channel. The negative carrier resides largely on the second nearest neighbor cation sites. The Ti atoms prefer not to sit on adjacent cation planes. Doping α-hematite with Ti atoms on alternate cation layers should lead to a ferrimagnetic semiconductor with a magnetic transition temperature of nearly 1000 K.

65 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of additional doping by Be on the properties of Ga1−xMnxAs (x=0.03) was investigated, and it was shown that the Curie temperature is observed to increase with increasing Be concentration.
Abstract: We have investigated the effect of additional doping by Be on the properties of Ga1−xMnxAs (x=0.03). For this relatively low value of x, the Curie temperature is observed to increase with increasing Be concentration. We show that the temperature dependence of the resistivity at zero magnetic field, including the resistivity maximum near the Curie temperature, can be successfully described by the magnetoimpurity scattering model proposed by Nagaev [Phys. Rep. 346, 387 (2001)] in both the paramagnetic and the ferromagnetic temperature regions. Quantitative analysis of the data in terms of this model yields the value of the p–d exchange energy |N0β|≈1.6 eV for Ga0.97Mn0.03As.

51 citations


Journal ArticleDOI
TL;DR: In this article, the binding energies from the Pb 4f 7/2 core levels decrease with increasing PbO content while the full-width at half-maximum of these peaks increase.
Abstract: X-ray photoelectron spectroscopy (XPS) has been used to obtain structural information on the x PbO · (1− x )V 2 O 5 glass system where x =0.22, 0.35, 0.43, and 0.54. The binding energies from the Pb 4f 7/2 and Pb 4f 5/2 core levels decrease with increasing PbO content while the full-width at half-maximum of these peaks increase. The O 1s spectra show an asymmetry for samples having composition x x =0.54, the O 1s spectrum was symmetric indicating that all three oxygen configurations have essentially the same binding energy. This behavior in addition to the decreasing binding energies of the Pb 4f levels with increasing PbO content suggest that the Pb–O bonds are becoming more covalent in nature and that eventually PbO changed its role from a glass modifier to a glass former for x >0.5. The asymmetric V 2p 3/2 peaks for the x 4+ ions in addition to V 5+ ions, while the symmetric V 2p 3/2 peaks for the more concentrated PbO vanadate glasses indicate only V 5+ being present. The concentration of V 4+ ions (0–4%) from the XPS data is consistent with determinations from magnetic susceptibility measurements on the same glass samples. In addition to the paramagnetic contribution (Curie–Weiss temperature-dependent behavior) from the V 4+ ions, the susceptibility for these oxide glasses consisted of a positive, constant contribution arising from the temperature-independent paramagnetic V 2 O 5 exceeding the diamagnetism from the core ions.

47 citations


Journal ArticleDOI
TL;DR: In this paper, the authors introduced a Heisenberg Hamiltonian for describing the magnetic properties of GaMnAs and compared the results obtained by using a realistic two-band model with those of a simplified parabolic two band model.
Abstract: We introduce a Heisenberg Hamiltonian for describing the magnetic properties of GaMnAs. Electronic degrees of freedom are integrated, leading to a pairwise interaction between Mn spins. Monte Carlo simulations in large systems are then possible, and reliable values for the Curie temperatures of diluted magnetic semiconductors can be obtained. Comparison of mean field and Monte Carlo Curie temperatures shows that fluctuation effects are important for systems with a large hole density and/or increasing locality in the carriers-Mn coupling. We have also compared the results obtained by using a realistic $\mathbf{k}\ensuremath{\cdot}\mathbf{p}$ model with those of a simplified parabolic two band model. In the two-band model, the existence of a spherical Fermi surface produces the expected sign oscillations in the coupling between Mn spins, magnifying the effect of fluctuations and leading to the eventual disappearance of ferromagnetism. In the more realistic $\mathbf{k}\ensuremath{\cdot}\mathbf{p}$ model, warping of the Fermi surface diminishes the sign oscillations in the effective coupling and, therefore, the effect of fluctuations on the critical temperature is severely reduced. Finally, by studying the collective magnetic excitations of this model at zero temperature, we analyze the stability of the fully polarized ferromagnetic ground state.

43 citations


Journal ArticleDOI
TL;DR: In this paper, the existence of a ferromagnetic state with the very high Curie temperature T C ≈500 K for a material with only s- and p-electrons as well as the nature of its underlying interaction are of great fundamental interest.
Abstract: The discovery of a ferromagnetic form of carbon (Nature 413 (2001) 716) gives a new perspective in the investigation of magnetic materials. The existence of a ferromagnetic state with the very high Curie temperature T C ≈500 K for a material with only s- and p-electrons as well as the nature of its underlying interaction are of great fundamental interest. Here we report on the observation of the ferromagnetically ordered state in a material obtained by high-pressure high-temperature treatment of the fullerene C60. It has a saturation magnetization more than four times larger than that reported previously. From our data we estimated the considerably higher value of T C ≈820 K .

42 citations


Journal ArticleDOI
TL;DR: In this paper, the results of magnetization measurements performed on single crystals of the pyrochlore compound Ho 2 Ti 2 O 7 were reported and the low-temperature magnetization curves for the three principal directions of an applied magnetic field were found to be in nearly perfect agreement with the predictions for a nearest-neighbor spin-ice model, contrary to previous reports.
Abstract: We report the results of magnetization measurements performed on single crystals of the pyrochlore compound Ho 2 Ti 2 O 7 . The low-temperature magnetization curves for the three principal directions of an applied magnetic field are found to be in nearly perfect agreement with the predictions for a nearest-neighbor spin-ice model, contrary to previous reports.

Journal ArticleDOI
TL;DR: In this paper, the effects of trivalent La substitution for divalent Ba on the magnetic properties of the double perovskite Ba2FeMoO6 polycrystalline Ba2−xLaxFeO6 samples have been prepared by the conventional solid-state reaction in a stream of 5% H2/Ar gas magnetization.
Abstract: We have investigated effects of the partial substitution of trivalent La for divalent Ba on the magnetic properties of the double perovskite Ba2FeMoO6 Polycrystalline Ba2−xLaxFeMoO6 samples have been prepared by the conventional solid-state reaction in a stream of 5% H2/Ar gas Magnetization (15 K, 5 kOe) is 26μB/fu for x=05 which is smaller than the value of 38μB/fu for x=0 The partial substitution of La3+ for Ba2+ considerably enhances the Curie temperature TC The TC increases from 316 K for x=0 to 336 K for x=05

Journal ArticleDOI
TL;DR: The spin-1/2 Cu2+ ions in β-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 β-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 (θCW = −135 K) indicates that the geometric frustration is largely relieved by the anisotropy

Journal ArticleDOI
TL;DR: A detailed study of the electronic transport and magnetic properties of Fe 1 - x Cu x Cr 2 S 4 (x≤0.5) on single crystals is presented in this paper.
Abstract: A detailed study of the electronic transport and magnetic properties of Fe 1 - x Cu x Cr 2 S 4 (x≤0.5) on single crystals is presented. The resistivity is investigated for 2≤T≤300 K in magnetic fields up to 140 kOe and underhydrostatic pressure up to 16 kbar. In addition magnetization and ferromagnetic resonance (FMR) measurements were performed. FMR and magnetization data reveal a pronounced magnetic anisotropy, which develops below the Curie temperature, T C , and increases strongly towards lower temperatures. Increasing the Cu concentration reduces this effect. At temperatures below 35 K the magnetoresistance, MR=[ρ(0) -ρ(H)]/ρ(0), exhibits a strong dependence on the direction of the magnetic field, probably due to an enhanced anisotropy. Applying the field along the hard axis leads to a change of sign and a strong increase in the absolute value of the magnetoresistance. On the other hand the magnetoresistance remains positive down to lower temperatures, exhibiting a smeared out maximum with the magnetic field applied along the easy axis. The results are discussed in the ionic picture using a triple-exchange model for electron hopping as well as a half metal utilizing a band picture.

Journal ArticleDOI
TL;DR: In this article, a number of oxide glasses containing Pr3+, Dy3+ and Nd3+ ions has been measured as a function of the magnetic field (0−50kOe) and temperature (5−300 K).

Journal ArticleDOI
TL;DR: In this paper, the structural phase transition induced by magnetic fields on the ferromagnetic compound MnAs was observed by the X-ray diffraction measurements in high magnetic fields up to 4 T.
Abstract: The structural phase transition induced by magnetic fields on the ferromagnetic compound MnAs was observed by the X-ray diffraction measurements in high magnetic fields up to 4 T. Magnetization measurements showed that Curie temperature TC was 315.5 K for increasing temperatures and a metamagnetic transition from the paramagnetic to the ferromagnetic state occurred above TC. The structural transformation from the hexagonal NiAs-type to the orthorhombic MnP-type structure was confirmed at TC with increasing temperature from 290 K. The X-ray profiles at 319 K in the magnetic field showed that the hexagonal structure phase appeared with increasing fields and coexisted with the orthorhombic one. On further increase of magnetic fields, the single phase of the hexagonal structure was observed above 3.5 T in the forced ferromagnetic state. Both the magnetic and structural transitions induced by magnetic fields above TC were first order with a hysteresis and had a close relationship between each other.

Journal ArticleDOI
TL;DR: In this article, measurements of the magnetic susceptibility χ, x-ray photoemission spectra (XPS), electrical resistivity ρ and electronic structure calculations for CeNi4B are reported.
Abstract: Measurements of the magnetic susceptibility χ, x-ray photoemission spectra (XPS), electrical resistivity ρ and electronic structure calculations for CeNi4B are reported. In the paramagnetic region, CeNi4B follows the Curie–Weiss law with µeff = 0.52µB/fu and θ = −10.7 K. The effective magnetic moment is lower than the free Ce3+-ion value. The Ce(3d) XPS spectra have confirmed the mixed-valence state of Ce ions in CeNi4B. The f occupancy, nf, and the coupling Δ between the f level and the conduction states were derived to be about 0.83 and 85 meV, respectively. Both susceptibility data and XPS spectra show that Ce ions in CeNi4B are in the intermediate-valence state. At low temperatures (below 12 K), the magnetic contribution to the electrical resistivity reveals a logarithmic slope characteristic of Kondo-like systems.

Journal ArticleDOI
TL;DR: In this article, a solid-state reaction was performed on RRhO3 (R=rare earth except Ce and Pm) and its crystallographic, magnetic, and electric properties were investigated.

Journal ArticleDOI
TL;DR: In this paper, four quaternary sulfides, namely, SrCu 2 M S 4 and EuCu 2 N S 4 (M =Ge and Sn), were prepared from a thoroughly ground mixture of EuS or SrS, Cu, or Sn, and S in stoichiometric proportions.

Journal ArticleDOI
TL;DR: A new thiospinel CuCrZrS4 has been successfully synthesized by a solid-state chemical reaction as discussed by the authors, which exhibits ferromagnetic properties below the Curie temperature at T c = 60 -2 K. This low magnetic-field behaviour indicates the existence of a reentrant spinglass phase below about 10 K.
Abstract: A new thiospinel CuCrZrS4 has been successfully synthesized by a solid-state chemical reaction. This CuCrZrS4 exhibits ferromagnetic properties below the Curie temperature at T c = 60 -2 K. The appearance of irreversible effect between field-cooled and zero-field-cooled magnetization is prominent below around 5 K in a magnetic field of less than 150 Oe. The ac susceptibility χAC shows a rapid decrease below about 10 K. This low magnetic-field behaviour indicates the existence of a re-entrant spin-glass phase below about 10 K. The dc magnetic susceptibility above 100 K shows Curie-Weiss behaviour with an effective magnetic moment of 3.61 μ B, which is a little less than the spin-only value of 3.87 μ B for the Cr3+ ion. The asymptotic Curie temperature θ P is approximately 65 K, which is a little higher than T c. The valence state is confirmed to be Cu+Cr3+Zr4+S4 2− on the basis of magnetic properties. The electrical resistivity ρ shows a semiconducting temperature dependence over the temperature range from...

Journal ArticleDOI
TL;DR: In this paper, the first-order field-induced itinerant-electron metamagnetic transition remains and brings about a large magnetic entropy change around room temperatures for the compounds.
Abstract: Magnetic properties and magnetic entropy change in La (Fe1-xMnx)11.7Si1.3Hy compounds have been investigated. A significant increase of the Curie temperature TC and a small increase of the saturation magnetizations µS have been observed after the introduction of interstitial H, which caused a slight volume expansion. The first-order field-induced itinerant-electron metamagnetic (IEM) transition remains and brings about a large magnetic entropy change around room temperatures for the compounds. The maximal magnetic entropy change is about 23.4, 17.7 and 15.9J/kgK under a magnetic field change from 0 to 5T for x=0.01, 0.02 and 0.03, respectively. Therefore, the compounds appear to be potential candidates for magnetic refrigerants around room temperatures.

Journal ArticleDOI
TL;DR: In this paper, the effect of a proper treatment of the disorder which includes all single-site multiple scattering appears to play a crucial role, while the standard RKKY calculation which neglects disorder, strongly underestimates the Curie temperature and is inappropriate to describe magnetism in DMS.
Abstract: Carrier induced ferromagnetism in diluted III-V semiconductor (DMS) is analyzed within a two-step approach. First, within a single site coherent-potential approximation formalism, we calculate the element resolved averaged Green's function of the itinerant carrier. Then using a generalized RKKY formula we evaluate the Mn-Mn long-range exchange integrals and the Curie temperature as a function of the exchange parameter, magnetic impurity concentration, and carrier density. The effect of a proper treatment of the disorder which includes all single-site multiple scattering appears to play a crucial role. The standard RKKY calculation which neglects disorder, strongly underestimates the Curie temperature and is inappropriate to describe magnetism in DMS. It is also shown that an antiferromagnetic exchange favors higher Curie temperature.

Journal ArticleDOI
TL;DR: In this paper, the Curie temperature of diluted (Ga,Mn)As magnetic semiconductors in the presence of As antisites is studied from first principles and the total energies associated with rotations of Mn-magnetic moments onto the effective classical Heisenberg Hamiltonian which is treated in the mean-field approximation to find the curie temperature.
Abstract: The Curie temperature of diluted (Ga,Mn)As magnetic semiconductors in the presence of As antisites is studied from first principles. We map total energies associated with rotations of Mn-magnetic moments onto the effective classical Heisenberg Hamiltonian which is treated in the mean-field approximation to find the Curie temperature. The presence of donors strongly reduces the Curie temperature and gives rise to a ground state with a partial disorder of local moments. We show that the observed dependence of the Curie temperature on the Mn concentration indicates that the concentration of As antisites increases with the Mn content.

Journal ArticleDOI
TL;DR: In this article, the magnetic properties of the electron doped manganites Ca1−x Yx MnO3 (for 0 ≤ x ≤ 0.25) in the paramagnetic regime were studied.
Abstract: We present a study of the magnetic properties of the electron doped manganites Ca1−x Yx MnO3 (for 0 ≤ x ≤ 0.25) in the paramagnetic regime. For the less doped samples (x ≤ 0.1) the magnetic susceptibility, χ(T), follows a Curie–Weiss (CW) law only for T > 450 K and, below this temperature, χ−1 (T) shows a ferrimagnetic-like curvature. We approached the discussion of these results in terms of a simple mean-field model where double exchange, approximated by a ferromagnetic Heisenberg-like interaction between Mn3+ and Mn4+ ions, competes with classical superexchange. For higher levels of doping (x ≥ 0.15), the CW behaviour is observed down to the magnetic ordering temperature (Tmo) and a better description of χ(T) was obtained by assuming full delocalization of the eg electrons. In order to explore the degree of delocalization as a function of T and x, we analysed the problem through Monte Carlo simulations. Within this picture we found that at high T the electrons doped are completely delocalized but, when Tmo is approached, they form magnetic polarons of large spin that cause the observed curvature in χ−1 (T) for x ≤ 0.1.

Journal ArticleDOI
TL;DR: In this article, the Curie-Weiss law was used to estimate the magnetic moment per Fe3+ cation of the cubic perovskite phases Sr2Fe1/− xGaxTaOO6.
Abstract: Powder samples of the magnetically diluted cubic perovskite phases Sr2Fe1 − xGaxTaO6 have been prepared by high temperature ceramic methods. X-Ray powder diffraction data show that the cations occupying the 6-coordinate site are chemically disordered in the range 0.10 ≤ x ≤ 0.40 and that increasing the Ga3+ concentration above this value leads to partial cation ordering between Ga3+ and Ta5+. Magnetic susceptibility data collected from these compounds can be fitted to the Curie–Weiss law, resulting in estimates of the magnetic moment per Fe3+ cation of between 4.57(1) (x = 0.20) and 6.37(1) μB (x = 0.90). The cause of the unexpectedly low paramagnetic moment observed in most of these compositions is ascribed to the effect of superexchange interactions extending beyond the adjacent 6-coordinate sites in the simple cubic lattice.

Journal ArticleDOI
TL;DR: In this article, single crystals of Pr 2 Te 4 O 11 have been grown through the reaction of Pr 6 O 11 and TeO 2 in a CsCl flux at 1123 K.

Journal ArticleDOI
TL;DR: In this paper, the temperature dependence of the 57 Fe Mossbauer recoilless fraction, and that of the local electronic and magnetic state of iron in the chalcogenide spinel FeCr 2 S 4 have been studied in detail around the Curie temperature with the help of 57 Fe Möller spectroscopy.

Journal ArticleDOI
TL;DR: In this article, the temperature dependence of the magnetic properties (i.e., ac magnetic permeability and magnetoimpedance voltage) for Fe-Co and Fe-Cr base nanocrystalline materials is analyzed.
Abstract: The temperature dependence of the magnetic properties (i.e., ac magnetic permeability and magnetoimpedance voltage) is analyzed for Fe-Co and Fe-Cr base nanocrystalline materials. Around the Curie point of the residual amorphous matrix a magnetic transition is detected, associated with the magnetic decoupling of ferromagnetic crystallites. The magnetic nature of such magnetic transition is analyzed within the framework of the random anisotropy model, taking into account the basic structural and magnetic characteristics of the constituent magnetic phases.

Journal ArticleDOI
TL;DR: In this paper, the structure and ionic conductivity of ruthenium diphosphates, ARu2(P2O7)2 A=Li, Na, and Ag, were investigated by single crystal X-ray diffraction techniques.

Journal ArticleDOI
TL;DR: A new potassium iron phosphate K 11 Fe 15 (PO 4 ) 18 O has been synthesized by the flux method and characterized by single-crystal X-ray diffraction as mentioned in this paper.