Showing papers on "Curie–Weiss law published in 1990"
TL;DR: In this article, the authors identified the origin of the ferromagnetic behavior in high-transition-temperature (high-Tc) copper oxide superconductors as being due to the presence of an impurity phase, La4Ba2Cu2O10 (the 422 phase) which is an insulator and is homologous to the green phase (Y2BaCuO5) found as an imurity in the Y-Ba-CuO 5 system.
Abstract: THERE have been a few reports of ferromagnetic behaviour in the high-transition-temperature (high-Tc) copper oxide superconductors For example, Na-doped La2CuO4 annealed in an inert gas, which is superconducting below 30 K, exhibits a ferromagnetic-like transition near 10 K (ref 1), although the origin of this behaviour is not clear In early studies we found that impure samples of LaBa2Cu3O7 prepared under a reduced oxygen atmosphere showed evidence of ferromagnetic-like behaviour near 5 K We have now identified the origin of the ferromagnetic behaviour as being due to the presence of an impurity phase, La4Ba2Cu2O10 (the 422 phase) This phase is an insulator and is homologous to the 'green' phase (Y2BaCuO5) found as an impurity in the Y–Ba–Cu–O system The 422 phase contains square-planar CuO4 units as do the high-Tc copper oxide superconductors, but in this compound each of these units lies perpendicular to those around it Magnetization measurements indicate an effective magnetic moment of 166µB per copper ion, with a saturation magnetic moment of 095 µB per Cu These results suggest that the compound is a localized ferromagnet in which the copper ions are magnetically ordered We suggest that the ferromagnetic coupling may originate in the orthogonality of the CuO4 units There may be analogies with K2CuF4, which is ferromagnetic below 65 K (ref 2) as a result of two-dimensional ordering of the d hole in Cu2+ arising from the Jahn–Teller interaction3 The 422 phase could provide flux-pinning centres in bulk superconducting LaBa2Cu3O7–y
55 citations
TL;DR: Direct connection can be made between pure and RMA exponents, which gives remarkable agreement with the experimental values, and a ferromagnetic scaling analysis applied to the line of transitions at {ital T}{sub {ital c}} results in a surprisingly good collapse of the magnetization data.
Abstract: The effects of a random component of the magnetocrystalline anisotropy on the magnetic properties and critical behavior of polycrystalline DyAl{sub 2} have been investigated using dc magnetic measurements. Random magnetic anisotropy (RMA) is produced by site-diluting ferromagnetic DyAl{sub 2} with the nonmagnetic, isomorphic intermetallic YAl{sub 2}. Dilution distorts the cubic Laves-phase unit cell because of a slight lattice mismatch thereby lowering the local crystal symmetry in a random fashion. Additional contributions to the RMA come from spin-orbit scattering by the conduction electrons. Hysteresis loops display little remanence and very small coercive fields, suggesting a weak RMA. This is consistent with estimates of the RMA strength {ital D} obtained using an approach of Chudnovsky {ital et} {ital al}. The magnetization at high temperatures ({ital T}{gt}4{ital T}{sub {ital c}}) is well described by a Curie-Weiss law. The paramagnetic Curie temperatures are positive, implying an average ferromagnetic exchange coupling between Dy ions, and increase with {ital x}. The paramagnetic moment shows no evidence of quenching across the series, thus confirming the well-localized nature of the 4{ital f} electronic orbitals. Low-field thermal scans of the bulk dc magnetization show no sign of a spontaneous moment for Dy concentrations 0.10{le}{ital x}{le}0.90, yet a sharp increasemore » in the magnetization occurs at a temperature {ital T}{sub {ital c}} that increases with {ital x}. A ferromagnetic scaling analysis applied to the line of transitions at {ital T}{sub {ital c}} results in a surprisingly good collapse of the magnetization data. By extension of prior theoretical work of Aharony and Pytte, a direct connection can be made between pure and RMA exponents, which gives remarkable agreement with the experimental values.« less
46 citations
TL;DR: In this paper, concentration effects on the temperature variation of ac susceptibility for a Fe3O4 ferrofluid were investigated and the results showed deviation from classical Langevin theory and a non-linear Curie-Weiss behaviour.
39 citations
TL;DR: In this paper, a misfit layer compound built of alternate double layers of CeS, approximately a {100} slice of NaCl type CeS and sandwiches of NbS2 with Nb in slightly distorted trigonal prisms of sulfur are described in centered orthorhombic lattices.
35 citations
TL;DR: The magnetic properties of MnCl2⋅H2O, a heretofore unexamined hydrate of manganese dichloride, have been studied in this paper.
Abstract: The magnetic properties of MnCl2⋅H2O, a heretofore unexamined hydrate of manganese dichloride, have been studied. The behavior is clearly distinguishable from that of the anhydrous material or either the dihydrate or the tetrahydrate. At high temperatures the susceptibility is Curie–Weiss‐like, with a Weiss constant θ=−4.9±0.3 K in χM=C/(T−θ); this may be compared with the values θ=−3.3 K for the anhydrous material, −14.5±0.3 K for the dihydrate (as determined in this work), and −1.8 K for the tetrahydrate. Departures from linearity occur below 20 K, and a broad maximum in the powder susceptibility appears at T(χmax)=3.60±0.10 K with χmax=0.304±0.003 emu/mol. The susceptibility drops sharply below 2.23 K, and ∂χ/∂T is a maximum at 2.16±0.01 K, which is identified with the Neel temperature Tc. Certain features of the data suggest two‐dimensional Heisenberg model behavior, for example the ratios Tc/‖θ‖=0.44 and Tc/T(χmax)=0.60. However, fits to χ(T) using a high‐temperature series expansion for the S=5/2 two‐dimensional square planar Heisenberg model are unconvincing, as are similar attempts based on a three‐dimensional model. In contrast, the model of a classical Heisenberg antiferromagnetic spin chain scaled to S=5/2 permits an excellent fit, with J/k=−0.49±0.04 K the intrachain exchange (in Hex=−2J∑i> jSi⋅S j). An interchain exchange of ‖J’/k‖=0.015±0.004 K, probably antiferromagnetic, can also be inferred, from the antiferromagnetic transition at Tc =2.16 K. The intrachain exchange is very similar to that in MnCl2⋅2H2O, while the interchain exchange is much weaker.
18 citations
TL;DR: Magnetic and Mossbauer effect studies have been reported for new UFe10Si2, UCo 10Si2 and UFe 10Mo2 compounds crystallizing with tetragonal structure of the ThMn12-type.
17 citations
TL;DR: In this paper, the properties of polycrystalline RSi2 compounds were investigated at temperatures ranging from 1.8 K to room temperature using superconducting quantum interference device (SQUID) magnetometry, ac susceptibility, resistivity, and magnetoresistance measurements.
Abstract: Magnetic and electrical properties of polycrystalline RSi2 compounds, where R=La‐Yb and Y, have been investigated at temperatures ranging from 1.8 K to room temperature using superconducting quantum‐interference device (SQUID) magnetometry, ac susceptibility, resistivity, and magnetoresistance measurements. Our data indicate that while PrSi2, ErSi2, and TmSi2 order ferromagnetically at 11, 2.8, and below 1.8 K, respectively, other RSi2 compounds with R=Nd, Eu, Gd, Tb, Dy, and Ho order antiferromagnetically with TN≤39 K. All compounds show Curie–Weiss behavior in the paramagnetic region and the effective moments are found to be close to the free‐ion values, gJ [J(J+1)]1/2. Another interesting feature is the observation of second transitions in the cases of Pr, Nd, Eu, Gd, Tb, and Dy compounds. SmSi2, CeSi2, and YbSi2 do not show any magnetic order down to 1.8 K. In the ordered state, all antiferromagnetic compounds have a T3 dependence of resistivity and show a positive magnetoresistance ranging from a few...
16 citations
TL;DR: Fe(110)/Ag(111) superlattices with Ag layer thickness of 30 or 60 A and various Fe layer thicknesses have been fabricated by high-rate sputtering and studied by x-ray diffraction magnetometries, and Mossbauer spectroscopy as mentioned in this paper.
Abstract: Fe(110)/Ag(111) superlattices with Ag layer thicknesses of 30 or 60 A and various Fe layer thicknesses have been fabricated by high‐rate sputtering and studied by x‐ray diffraction magnetometries, and Mossbauer spectroscopy. A slightly enhanced magnetic moment and hyperfine field, and a reduced Tc have been observed in samples with thin Fe layers. The magnetization exhibits a BT3/2 dependence with very large values of B.
15 citations
TL;DR: Magnetization and Mossbauer effect studies of quasicrystals have been carried out in this article, where the effects of Fe substitution on the magnetic properties were investigated.
Abstract: Magnetization and Mossbauer‐effect studies of ferromagnetic Al‐Mn‐Si and Al‐Mn‐Cu‐Ge quasicrystals are presented. All alloys show paramagnetic or spin‐glass behavior in addition to ferromagnetism at low temperatures. The effects of Fe substitution on the magnetic properties were investigated. Possible models for ferromagnetic order in quasicrystals are discussed.
11 citations
TL;DR: In this paper, the authors investigated the Nd 2 Fe 14− x Co x B system by means of X-ray and neutron diffraction, metallographic techniques and bulk magnetic measurements.
Abstract: We have investigated the Nd 2 Fe 14− x Co x B system by means of X-ray and neutron diffraction, metallographic techniques and bulk magnetic measurements. The tetragonal structure of Nd 2 Fe 14 B exists in the entire range x = 0–14. The lattice constants decrease with increasing cobalt content. The replacement of iron by cobalt raises the Curie temperature. The magnetic structure of Nd 2 Fe 13 Co 1 B has been investigated at 740 K (above the Curie temperature), at 293 K (room temperature) and at 30 K (low temperature). The magnetic moments are parallel to the c axis and do not show any reorientation tendency with temperature. For low cobalt concentrations, cobalt atoms are more probably statistically distributed on the iron point positions.
10 citations
TL;DR: The magnetic properties of polycrystalline Fe3−xVxAl alloys with x ≥ 0.8 having atomically disordered structure of the A2 type were investigated by magnetostatic and Mossbauer methods as discussed by the authors.
Abstract: The magnetic properties of polycrystalline Fe3−xVxAl alloys with x≤0.8 having atomically disordered structure of the A2 type were investigated by magnetostatic and Mossbauer methods. It was ascertained that the magnetic moment and the Curie temperature decrease approximately linearly with increasing x. Above the Curie temperature investigated alloys do not obey the Curie-Weiss law. Marked nonlinear variations of magnetic susceptibility with magnetic field intensity indicate the existence of magnetic clusters. Mossbauer investigations also confirmed the existence of magnetic clusters with short relaxation time.
TL;DR: In this article, the exact solution for the s-d model by the Bethe-ansatz method was used to obtain the free energy, entropy, specific heat, magnetization and susceptibility of a magnetic impurity.
Abstract: Using the exact solution for the s-d model by the Bethe-ansatz method, the free energy, entropy, specific heat, magnetization and susceptibility of a magnetic impurity are obtained numerically as a function of temperature and magnetic field. In particular, detailed investigation and analysis of the high temperature and high magnetic field property are carried out.
TL;DR: In this paper, the temperature dependence of the g value, linewidth and integral intensity of a Bi(Pb)-Sr-Ca-Cu-O ceramic superconductor was studied under two different spectrometer modes: a conventional field-modulation mode and a direct reflection-amplitude mode.
Abstract: ESR absorption at 22.9 GHz of the high-Tc phase of a Bi(Pb)-Sr-Ca-Cu-O ceramic superconductor has been studied under two different spectrometer modes: a conventional field-modulation mode and a direct reflection-amplitude mode. Owing to the effect of hysteresis in the microwave response, the field modulation did not provide the proper field derivative of ESR absorption. By employing the direct mode, we were able to obtain more reliable data for the temperature dependence of the g value, linewidth and integral intensity. The spin susceptibility followed the Curie-Weiss behavior with the negative Weiss temperature around -4 K.
TL;DR: In this paper, the magnetic properties of the compounds were analyzed and correlated with their composition, and it was shown that the tetragonal Nd2Fe14B-type structure exists only for x ⩽ 0.5.
TL;DR: In this article, the properties of Nd2Fe14-xMxB systems (M = Si, Cr and Cu) were investigated and the temperature-composition diagrams of spin arrangements appearing in these systems were established.
TL;DR: In this paper, the basic magnetic properties of Pb2Sr2Y1-xCaxCu3O8+ delta have been studied and a lower critical field Hc1 has been determined for the magnetic field oriented perpendicular (Hperpendicular to ) and parallel to (H/sub ///) to the Cu-O planes.
Abstract: Basic magnetic properties of Pb2Sr2Y1-xCaxCu3O8+ delta have been studied. Results of the measurements of the AC susceptibility of the powder samples with x=0.2-0.8 and DC magnetic moment and susceptibility of the Pb2Sr2Y0.7Ca0.3Cu3O8+ delta single crystal are presented. Temperature dependence of the magnetic moment in various cooling procedures was measured. Zero-field cooling (ZFC), field cooling (FC) and remanent (REM) magnetic moments are given. A lower critical field Hc1 has been determined for the magnetic field oriented perpendicular (Hperpendicular to ) and parallel to (H/sub ///) to the Cu-O planes. A new more sensitive procedure of Hc1 determination has been proposed.
Patent•
12 Sep 1990TL;DR: In this paper, the Curie points of ferromagnetic materials were determined by means of a conventional thermal analyzer with externally added facilities to provided an external magnetic field, which increased the magnetic anisotropy energy and strengthened the spontaneous magnetization of the materials.
Abstract: A method and the instrument associated therewith for determining the Curie points of ferromagnetic materials which display no significant abrupt change in heat absorption around the Curie points thereof by means of a conventional thermal analyzer with externally added facilities to provided an external magnetic field. The abrupt change of heat absorption of the ferromagnetic materials is increased by adding the external magnetic field to increase the magnetic anisotropy energy thereof and to strengthen the spontaneous magnetization thereof.
TL;DR: In this article, a novel approach for the classical description of the dynamics of magnetic systems in the presence of thermal agitation is proposed, and the closed nonlinear differential equation for the average magnetization is obtained.
Abstract: A novel approach for the classical description of the dynamics of magnetic systems in the presence of thermal agitation is proposed. The closed nonlinear differential equation for the average magnetization is obtained. The relation between longitudinal and transversal relaxation frequencies, is obtained. The domain wall structure and propagation near the Curie temperature are investigated. A new type of critical behavior of the wall motion is explored. >
TL;DR: In this paper, the magnetic moment and hyperfine field data at liquid He temperatures were used to determine the magnetic field moments on Fe and Cr as a function of the Cr concentration.
TL;DR: In this article, electrical resistivity and magnetic susceptibility measurements are reported for all amorphous alloys and quasicrystalline samples with x≥10 reveal Curie-like magnetic susceptibility and electrical resistivities dominated by structural scattering.
Abstract: Alloys of the series Ti56Ni28−xFexSi16 (x=0,...,20) can be prepared either in the amorphous phase or as single phase quasicrystals by rapid solidification. Here electrical resistivity and magnetic susceptibility measurements are reported. All amorphous alloys and quasicrystalline samples with x≥10 reveal Curie‐like magnetic susceptibility and electrical resistivity dominated by structural scattering. The quasicrystalline samples with x<10 demonstrate nonCurie susceptibility and a minimum in ρ(T) where Tmin varies inversely with Fe content.
TL;DR: Magnetic susceptibility, magnetization and electrical resistivit are investigated on the ternary arsenides CrRhAs and CrRuAs in this article, where the former compound is antiferromagnetic with a Neel temperature T N = 165 K, while the latter one is ferromagnetic having a Curie temperature T c = 164 K.
TL;DR: In this article, low-temperature measurements of the magnetic susceptibility, plasma reflectivity and Hall effect as a function of carrier-concentration were performed on Pb1-x-ySnxMnyTe samples with x=0.72 and y= 0.08.
Abstract: Low-temperature measurements of the magnetic susceptibility, plasma reflectivity and Hall effect as a function of carrier-concentration were performed on Pb1-x-ySnxMnyTe samples with x=0.72 and y=0.03, 0.06, 0.08. The dependences of the paramagnetic Curie temperature and effective mass of holes on manganese content and carrier concentration were determined. The analysis of the experimental data has been performed assuming that two valence bands are relevant in the case of PbSnMnTe: the non-parabolic light-hole L band and the parabolic heavy-hole Sigma band. Theoretical calculations of the paramagnetic Curie temperature dependences on manganese content and carrier concentration were also performed on the basis of the band structure model mentioned above and assuming the RKKY exchange interaction between Mn spins. It was found that the compositional evolution of the band structure determined the carrier concentration dependence of the magnetic properties of PbSnMnTe.
TL;DR: In this paper, the properties of amorphous ribbons of Co0.93−yNiyFe0.07)75Si15B10 with y up to 0.93 are described.
TL;DR: In this article, the transverse susceptibility was measured in polycrystalline soft ferrimagnetic ring samples and it was shown that the very peculiar shape of the transversal susceptibility curve comes form the combination of two magnetization processes: the 180 degrees domain-wall motions which give rise to the initial susceptibility, and the sudden rotation of domains magnetized perpendicular to the applied field when a certain threshold of the biasing field is reached.
Abstract: The transverse susceptibility was measured in polycrystalline soft ferrimagnetic ring samples. It is shown that the very peculiar shape of the transverse susceptibility curve comes form the combination of two magnetization processes: the 180 degrees domain-wall motions which give rise to the initial susceptibility, and the sudden rotation of domains magnetized perpendicular to the applied field when a certain threshold of the biasing field is reached. The temperature dependence of this threshold has been investigated and has shown a close connection with the effective anisotropy field. >
TL;DR: In this article, the influence of the temperature and the Cr-content of metallic foils was discussed and the coefficientB 3/2 in Bloch's law was calculated, and the Curie and crystallization temperature were taken from the DTA-DTMG method.
Abstract: Spectra of metallic foils Fe80−x
Cr
x
B2 (x=6, 10, 15, 20) and Fe60Cr20B12Si8 were measured at range 4.2 K–300 K. Mossbauer data were analysed by Window’s Hesse-Rubartsch’s and Janot’s methods. The influence of the temperature and the Cr-content is discussed. The coefficientB
3/2 in Bloch’s law was calculated. Curie and crystallization temperature were taken from the DTA-DTMG method [1]. For finding the Curie temperature of the sample Fe60Cr20B20 we used ac susceptibility, but this sample is not homogeneous.
TL;DR: Magnetic susceptibility measurements on NpB 2, PuB 2 and their solid-solutions are reported in this article, and confirm the previously published Mossbauer spectroscopy investigations.
TL;DR: In this paper, the RKKY model was used to interpret the changes of the paramagnetic Curie temperature and the excess effective magnetic moment with composition of Gd 1− x Lu x Al 2.
TL;DR: In this article, the authors measured the high field magnetization of oxygen-depleted Ba2YCu3Oy (y=6.34) using a pulse magnet to clarify the origin of the Curie-Weiss term of its magnetic susceptibility.
Abstract: The high field magnetization of oxygen-depleted Ba2YCu3Oy (y=6.34) is measured up to 350 kOe using a pulse magnet to clarify the origin of the Curie-Weiss term of its magnetic susceptibility. Analysis of the high field magnetization curve reveals that the Curie-Weiss term is a result of the isolated Cu2+ (S= 1 2 ) . On the basis of experimental results, the valence states of Cu ions in the CuO chain in the Ba2YCu3Oy system are discussed.
TL;DR: In this paper, the magnetic properties of amorphous Co 100-x Y x (50? x? 70) alloys prepared by a melt-quenching method were studied.
Abstract: The magnetic properties of amorphous Co 100-x Y x (50 ? x ? 70) alloys prepared by a melt-quenching method were studied. Based on the results derived from the Co-Y alloys, the magnetic moment of Co and the Curie temperature in amorphous Co 100-x R x (R = Pr, Nd, Sm, Gd, Dy, Er) alloys are discussed. The Co atoms no longer sustain a moment when x ? 60. The exchange integral between R and R atoms or between R and Co atoms rapidly decreases as the atomic number of the lanthanide element increases.
TL;DR: In this paper, the influence of random fluctuations in modulation amplitude, thickness of layers, and width of interdiffusion zones on the Curie temperature of compositionally modulated magnetic films is studied in the molecular field approximation.
Abstract: The influence of random fluctuations in modulation amplitude, thickness of layers, and width of interdiffusion zones on the Curie temperature of compositionally modulated magnetic films is studied in the molecular field approximation. The Curie temperature has been found to be most sensitive to the fluctuations in the modulation amplitude, which give rise to some kind of localized magnetism in the film. >