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Showing papers on "Curie temperature published in 1997"


Journal ArticleDOI
TL;DR: In this article, a giant magnetocaloric effect (ΔSmag) has been discovered in the Gd5(SixGe1−x)4 pseudobinary alloys, where x⩽0.5 is the largest order phase transformation.
Abstract: A giant magnetocaloric effect (ΔSmag) has been discovered in the Gd5(SixGe1−x)4 pseudobinary alloys, where x⩽0.5. For the temperature range between ∼50 and ∼280 K it exceeds the reversible (with respect to alternating magnetic field) ΔSmag for any known magnetic refrigerant material at the corresponding Curie temperature by a factor of 2–10. The two most striking features of this alloy system are: (1) the first order phase transformation, which brings about the large ΔSmag in Gd5(SixGe1−x)4, is reversible with respect to alternating magnetic field, i.e., the giant magnetocaloric effect can be utilized in an active magnetic regenerator magnetic refrigerator; and (2) the ordering temperature is tunable from ∼30 to ∼276 K by adjusting the Si:Ge ratio without losing the giant magnetic entropy change.

657 citations


Journal ArticleDOI
Zhao Huang1, Y. Cao1, Y. Y. Sun1, Y.Y. Xue1, Ching-Wu Chu1 
TL;DR: Anomalies in the dielectric constant and loss tangent have been observed in the ferroelectromagnet YMnO{sub 3} near its N{acute e}el temperature of {approximately}80 K and below its ferroelectric Curie temperature of{approximately}914 K as mentioned in this paper.
Abstract: Anomalies in the dielectric constant and loss tangent have been observed in the ferroelectromagnet YMnO{sub 3} near its N{acute e}el temperature of {approximately}80 K and below its ferroelectric Curie temperature of {approximately}914 K. These anomalies are indicative of coupling between the ferroelectric and antiferromagnetic orders in this compound. A small but distinct magnetoelectric effect and a magnetoresistive effect up to {approximately}15{percent} were also detected in a magnetic field at 5 T. The results will be contrasted with previous theoretical predictions. {copyright} {ital 1997} {ital The American Physical Society}

440 citations


Journal ArticleDOI
TL;DR: The metal-insulator transition is attributed to a modification of the spin-dependent potential J HsnS associated with the onset of magnetic order at the Curie point TC as discussed by the authors.
Abstract: The metal-insulator transition is mixed-valence manganites of the ~La0.7Ca0.3!MnO3 type is ascribed to a modification of the spin-dependent potential J HsnS associated with the onset of magnetic order at TC . Here JH is the on-site Hund’s-rule exchange coupling of an e g electron with s51/2 to the t 2g ion core with S 53/2. Above TC, the e g electrons are localized by the random spin-dependent potential and conduction is by variable-range hopping. Over the whole temperature range, the resistivity varies as ln( r/r ‘) 5@T0$12( M/ MS) 2 %/T# 1/4 , where M/ MS is the reduced magnetization. The temperature and field dependence of the resistivity deduced from the molecular-field theory of the magnetization reproduces the experimental data over a wide range of temperature and field. @S0163-1829~97!04513-X# Interest in mixed-valence manganites of the ~La0.7Ca0.3!MnO3 type has revived 1 with the observations of large negative magnetoresistive effects, 2,3 especially in suitably annealed thin films. 4 The magnetoresistance is greatest in the vicinity of the Curie point TC of ferromagnetic compositions which exhibit ‘‘metallic’’ ~temperatureindependent! conduction at low temperatures and thermally activated conduction above TC . These compositions have a structure which is a variant of the cubic perovskite cell where the Mn-O bond lengths are unequal and Mn-O-Mn bond angles differ from 180 °. 5 Their electronic properties are re

427 citations


Journal ArticleDOI
TL;DR: The temperature and field-dependent permittivities of fiber-textured Ba0.7Sr0.3TiO3 thin films grown by liquid-source metalorganic chemical vapor deposition were investigated as a function of film thickness as discussed by the authors.
Abstract: The temperature- and field-dependent permittivities of fiber-textured Ba0.7Sr0.3TiO3 thin films grown by liquid-source metalorganic chemical vapor deposition were investigated as a function of film thickness. These films display a nonlinear dielectric response under conditions representative of those encountered in dynamic random access memories or other integrated capacitor applications. This behavior has the exact form expected for a classical nonlinear, nonhysteretic dielectric, as described in terms of a power series expansion of the free energy in the polarization as in the Landau–Ginzburg–Devonshire approach. Curie–Weiss-like behavior is exhibited above the bulk Curie point (∼300 K), although the ferroelectric phase transition appears frustrated. Small-signal capacitance measurements of films with different thicknesses (24–160 nm) indicate that only the first term in the power series expansion varies significantly with film thickness or temperature. Possible origins for this thickness dependence are...

373 citations


Journal ArticleDOI
TL;DR: In this article, the effect of different alloying additions substituting for nonmagnetic Si and Ge on the giant magnetocaloric effect observed for the compound Gd5(Si2Ge2) was studied.

301 citations


Journal ArticleDOI
Akihisa Inoue1
TL;DR: In this article, a review of the recent findings of bulk amorphous alloys with soft or hard magnetism at room temperature is presented, where the authors show that soft magnetic properties combined with large glass-forming ability (GFA) were obtained in Fe 72 Al 5 Ga 2 P 11 C 6 B 4 and Fe 72 al 5 Ga 6 B4 Si 1 amorphized alloys.
Abstract: This paper reviews our recent findings of bulk amorphous alloys with soft or hard magnetism at room temperature. Soft magnetic characteristics combined with large glass-forming ability (GFA) were obtained in Fe 72 Al 5 Ga 2 P 11 C 6 B 4 and Fe 72 Al 5 Ga 2 P 10 C 6 B 4 Si 1 amorphous alloys. The maximum thickness for glass formation by copper mold casting was about 3 mm. These bulk amorphous alloys have a Curie temperature (T c ) of 600–606 K in an annealed state and their soft magnetic properties are about 1.1 T for saturation magnetization (B s ) and 2–6 A m −1 for coercive force (H c ). The thick amorphous sheets up to 180 gmm in thickness exhibit high permeability of 7000–12 000 at 1 kHz. On the other hand, the hard magnetic properties were obtained for amorphous Ln 60 Fe 30 Al 10 (Ln = Nd or Pr) cylinders with diameters below 15 mm. The large GFA is due to the high T x /T m of 0.85–0.90 and the small temperature intervals of 85–140 K between T m and T x . The T c is around 600 K and typical magnetic properties are 0.13 T for remanence, 0.15 T for B s , 280 k A m −1 for H c and 19 kJ m −3 for (JH) max . The hard magnetic properties disappear in the crystallized state. The first success of synthesizing the ferromagnetic bulk amorphous alloys is important for future progress of basic science and applications.

212 citations


Journal ArticleDOI
TL;DR: Graphitically encapsulated ferromagnetic Ni nanocrystals have been synthesized via a modified tungsten arc discharge method as mentioned in this paper, which is stable against environmental degradation, including extended exposure to strong acids.
Abstract: Graphitically encapsulated ferromagnetic Ni nanocrystals have been synthesized via a modified tungsten arc-discharge method. By virtue of the protective graphitic coating, these nanocrystals are stable against environmental degradation, including extended exposure to strong acids. The magnetic properties of the encapsulated particles are characterized with regard to the nanoscale nature of the particles and the influence of the graphitic coating which is believed to be benign insofar as the intrinsic magnetic properties of the encapsulated nanocrystals are concerned. The Curie temperature of graphitically encapsulated Ni nanocrystals is the same as that of microcrystalline Ni. However, saturation magnetization, remanent magnetization, and coercivity of these particles are reduced, for a range of temperatures. The unique features are compared with those of unencapsulated nanocrystalline and coarse microcrystalline nickel particles.

208 citations


Journal ArticleDOI
TL;DR: In this paper, the magnetic and structural properties of epitaxial bcc Fe(001) films grown at 175 C on molecular-beam epitaxy-prepared GaAs(001)-2*4 and -c(4*4) reconstructed surfaces, with film thicknesses ranging up to ~30 ML (~43 ).
Abstract: : We have studied the magnetic and structural properties of epitaxial bcc Fe(001) films grown at 175 C on molecular-beam epitaxy-prepared GaAs(001)-2*4 and -c(4*4) reconstructed surfaces, with film thicknesses ranging up to ~30 ML (~43 ). We present measurements of the thickness-dependent evolution of the magnetic properties of the Fe films as determined by in situ magneto-optic Kerr effect. We find that the magnetic properties and growth mode are similar for both 234 and c(434) reconstructions, although the initial adsorption sites and island nucleation as measured by scanning tunneling microscopy are clearly dominated by the substrate surface reconstruction. The onset of room-temperature ferromagnetism occurs at 6 ML for growth on both GaAs surface reconstructions. At this coverage, the measured Curie temperature (100 C) is significantly reduced from that of bulk alpha-Fe (770 C). The anisotropy is dominated by a uniaxial component such that the two (110) axes are inequivalent for all coverages studied. Shape anisotropy does not appear to play a significant role.

173 citations


Journal ArticleDOI
TL;DR: In this paper, a simple model for itinerant magnetism in the ferromagnetic transition metals is proposed, which incorporates both the energy of moment formation and the order of moment ordering, and the parameters of the model are determined from first-principles density-functional calculations.
Abstract: We propose a simple model for itinerant magnetism in the ferromagnetic transition metals. The model incorporates both the energy of moment formation, and the energy of moment ordering. The parameters of the model are determined from first-principles density-functional calculations for the ferromagnetic state and a number of spin spiral states. The simplicity of the magnetic energy functional allows extensive Monte Carlo simulations to be performed. Results for the finite-temperature magnetic properties of body-centered-cubic Fe, and face-centered-cubic Co and Ni are presented.

171 citations


Journal ArticleDOI
TL;DR: In this paper, the authors show that negative magnetoresistance (CMR) occurs in manganites at a first-order ferromagnetic transition and that the CMR is greatest near t≈0.98 where the transition at TC is first order.
Abstract: A “colossal” negative magnetoresistance (CMR) occurs in manganites at a first-order ferromagnetic transition. The Mn4+ and high-spin Mn3+ ions each contain localized t3 configurations; the t3–pπ–t3 superexchange interactions are antiferromagnetic. The orbital degeneracy of localized Mn3+:t3e1, 5Eg configurations is lifted by cooperative static or dynamic Jahn–Teller deformations. Strong e-electron coupling to oxygen displacements, static or dynamic, introduces ferromagnetic e1–pσ–e0 interactions either via superexchange or, for fast Mn3+ to Mn4+ electron transfer relative to the spin-relaxation time (τh ωR−1 to τh<ωR−1 occurs within mobile molecular units, where Wσ is the bandwidth for states of e-orbital parentage and ωR−1 is the period of the optical-mode lattice vibration that traps a mobile hole as a small-polaron Mn4+ ion. TC increases with the fraction of double-exchange couplings, and this fraction increases with Wσ and ωR at the transition from polaronic to itinerant-electron behavior below TC. The bandwidth Wσ∼eσλσ2 cos φ〈cos(θij/2)〉 depends on the covalent mixing parameter λσ, which increases with pressure, as well as on the Mn–O–Mn bond angle (180°−φ), which increases with the tolerance factor t that measures the equilibrium bond-length mismatch, and on the angle θij between neighboring spins so that Wσ increases with the spontaneous magnetization on cooling below TC. In the compositions Ln0.7A0.3MnO3 with A=Ca or Sr, TC increases with t over the range 0.96⩽t⩽0.98 where the transition at TC is first order. The CMR is greatest near t≈0.96; it reflects a trapping out of mobile holes with decreasing temperature in the paramagnetic phase and their progressive release with decreasing temperature in the ferromagnetic phase where spin entropy is exchanged for configurational entropy.

167 citations


Journal ArticleDOI
TL;DR: In this article, a systematic study of the magnetic properties of the manganites Ln0.5A 0.5MnO3 (A,A′)0.
Abstract: A systematic study of the magnetic properties of the manganites Ln0.5(A,A′)0.5MnO3 (A,A′=Ba, Ca, Sr) has been carried out. The variations of TC and TN vs two parameters, the average size of the interpolated cations 〈rA〉 and the mismatch effect represented by the variance σ2, have been studied for the series of manganites La0.5(A,A′)0.5MnO3, Pr0.5(A,A′)0.5MnO3, Nd0.5(A,A′)0.5MnO3 and Sm0.5(A,A′)0.5MnO3 (A,A′=Ba, Ca, Sr), involving at most three different cations on the perovskite A site. The results obtained for other (Ln, Ln′)0.5Sr0.5MnO3(Ln, Ln′=Gd, Sm Y, Pr) have been taken into consideration. A σ2−〈rA〉 diagram has been established, which displays the different types of magnetic behaviors that can be exhibited by Ln0.5A0.5MnO3 manganites, i.e., when the temperature is decreasing, either a paramagnetic (PM) to ferromagnetic (FM) transition, or PM to FM followed by FM to antiferromagnetic transitions, or a PM to weak ferromagnetic transition.

Journal ArticleDOI
TL;DR: In this paper, a wide supercooled liquid region before crystallization and good soft magnetic properties were found for Fe-based amorphous alloys in Fe-Co-Ni-Zr-B system.
Abstract: New Fe-based amorphous alloys in Fe-Co-Ni-Zr-B system exhibiting a wide supercooled liquid region before crystallization and good soft magnetic properties were found to be formed by melt spinning. The composition range of the amorphous (Fe 1-x-y Co x Ni y ) 70 Zr 10 B 20 alloys with the wide supercooled liquid region above 50 K extends from 0 to 36 at%Co and 0 to 30%Ni and the largest value of the supercooled liquid region defined by the difference between the glass transition temperature (T g ) and crystallization temperature (T x ), ΔT x ( = T x - T g ) is 68 K for Fe 56 Co 7 Ni 7 Zr 10 B 20 . The crystallization from the supercooled liquid of the Fe 56 Co 7 Ni 7 Zr 10 B 20 alloy upon continuous heating occurs through a single stage and the resulting crystallized structure consists of α-Fe, Fe2Zr and Fe 3 B phases containing Co and Ni elements. These Fe-based amorphous alloys exhibit good soft magnetic properties and the saturation magnetization, coercive force, permeability at I kHz and Curie temperature are respectively 0.96 T, 2.41 A/m, 17700 and 567 K for the amorphous Fe 56 Co 7 Ni 7 Zr 10 B 20 alloy annealed for 600 s at 750 K. The finding of the Fe-based amorphous alloys with good soft magnetic properties and high thermal stability of the supercooled liquid is important for future development of ferromagnetic bulk amorphous alloys.

Journal ArticleDOI
TL;DR: In this paper, the formation mechanism of the core-shell structure of a BaTiO3(BT) and MgO-Ho2O3-based system was studied.
Abstract: The formation mechanism of the core-shell structure of a BaTiO3(BT)–MgO–Ho2O3-based system was studied. Mg reacted with BT at low temperatures and showed poor diffusivity compared with Ho. The core-shell structure was considered to be formed by the suppression of the diffusion of Ho into the core region by Mg. Also, replacement modes of Mg and Ho in perovskite were investigated. Lattice parameters were determined at temperatures higher than the Curie temperature in order to avoid crystal structure change. It was confirmed that Mg dissolved in Ti site, and Ho dissolved in both Ba and Ti sites. This indicates that Mg ions act as acceptors and Ho ions act as both donors and acceptors in the shell phase.

Journal ArticleDOI
TL;DR: For a La 0.8Sr0.2MnO3 film with a grain boundary angle θ=36.8° a field independent component r0=4.1×10−6
Abstract: Epitaxial ferromagnetic manganite films have been sputtered on bicrystal substrates. Their magnetoresistance was measured as a function of magnetic field and temperature. The grain boundary magnetoresistance at low temperature is separated from the intrinsic magnetoresistance near the Curie temperature. The grain boundary magnetoresistance peaks at about 100 Oe and saturates at about 2 kOe. For a La0.8Sr0.2MnO3 film with a grain boundary angle θ=36.8° a field independent component r0=4.1×10−6 Ω cm2 was separated from a field-dependent component which has its maximum rH=2.3×10−6 Ω cm2 for H of order the coercive field.

Journal ArticleDOI
TL;DR: In this article, the variation of the Curie temperature and the antiferromagnetic transition temperature as a function of the average size of the A site cations (Ln, Sr) in the manganite perovskites Ln0.5Sr 0.5MnO3 was studied.
Abstract: We have studied the variation of the paramagnetic to ferromagnetic transition temperature TC and of the ferromagnetic to antiferromagnetic transition temperature TN as a function of the average size of the A site cations (Ln, Sr) in the manganite perovskites Ln0.5Sr0.5MnO3 (Ln=Gd, Sm, Y, Pr, La). For our investigation we used dc resistivity, magnetization, susceptibility and magnetoresistance measurements. Results show that the Curie temperature TC increases from 85 to 310 K when 〈rA〉 varies from 1.221 to 1.263 A, whereas TN remains stable around 150 K. A magnetic phase diagram temperature-〈rA〉 has been established, allowing five regions with different magnetic behaviours to be evidenced: paramagnetic insulating, ferromagnetic metallic, antiferromagnetic insulating, canted antiferromagnetic metallic, and weak ferromagnetic insulating. The extension of these regions is determined by the value of the applied magnetic field.

Journal ArticleDOI
TL;DR: Spin-polarized photoemission has developed into a versatile tool for the study of surface and thin film magnetism as discussed by the authors, and its application to a number of different problems, including both valence band and core level studies.
Abstract: Spin-polarized photoemission has developed into a versatile tool for the study of surface and thin film magnetism. In this review, we examine the methodology of the technique and its application to a number of different problems, including both valence band and core level studies. After a detailed review of spin-polarization measurement techniques and the related experimental requirements we consider in detail studies of the bulk properties both above and below the Curie temperature. This section also includes a discussion of observations relating to unique metastable phases obtained via epitaxial growth. The application of the technique to the study of surfaces, both clean and adsorbate covered, is reviewed. The report then examines, in detail, studies of the spin-polarized electronic structure of thin films and the related interfacial magnetism. Finally, observations of spin-polarized quantum well states in non-magnetic thin films are discussed with particular reference to their mediation of the oscillatory exchange coupling in related magnetic multilayers.

Journal ArticleDOI
TL;DR: In this paper, a phenomenological theory is presented to describe ferroelectric superlattices with first-order phase transitions, which depend sensitively on the interfacial coupling and the thickness of the component slabs.
Abstract: A phenomenological theory is presented to describe ferroelectric superlattices with first-order phase transitions. Static properties including the Curie temperature, spontaneous polarization and dielectric susceptibility are discussed with model parameters appropriate to ${\mathrm{BaTiO}}_{3}$/${\mathrm{PbTiO}}_{3}$. When the strength of interfacial coupling is weak, a size-driven phase transition still occurs with decreasing periodicity of the superlattice. The properties depend sensitively on the interfacial coupling and the thicknesses of the component slabs. The dielectric susceptibility is very different from the result for a simple series connection, especially in the high-temperature range, and can be designed flexibly by varying the layering sequence.

Journal ArticleDOI
TL;DR: In this paper, the dielectric susceptibility of perovskite ferroelectrics with the stable polar phase in situations where the influence of depolarizing field can be neglected was derived for a three dimensional case.
Abstract: The characteristic sizes of perovskite ferroelectrics have been examined by mean-field theory in a three dimensional base, leading to a detailed evaluation of the ultimate limits of physical sizes in nanostructured ferroelectrics with the stable polar phase in situations where the influence of depolarizing field can be neglected. Consequently, the dielectric susceptibility of nanostructured ferroelectrics is also derived for a three dimensional case. The size dependencies on the phase transition temperatures of perovskite ferroelectris, such as BaTiO3, PbTiO3, and Pb(Zr0.5Ti0.5)O3, are calculated by considering crystallographic anisotropy. In addition we have numerically evaluated the dielectric coefficient of Pb(Mg,Nb)O3 near the Curie temperature range based on its microstructure.

Journal ArticleDOI
TL;DR: In this article, a temperature-sensitive magnetic fluid with a low Curie temperature is synthesized, characterized by x-ray diffraction, magnetization, and small angle neutron scattering (SANS).
Abstract: A temperature-sensitive magnetic fluid with a low Curie temperature is synthesized. The fluid is characterized by x-ray diffraction, magnetization, and small angle neutron scattering (SANS). Low Curie temperature of the fluid enables us to separate out the nuclear and magnetic scattering contributions in SANS by recording the SANS pattern at two temperatures.

Journal ArticleDOI
TL;DR: In this article, a polycrystalline perovskite with composition La0.7Ca0.3Fe0.95O3 has been produced by standard ceramic method and a qualitative discussion of the effect in magnetic and transport properties of these compounds, caused by the substitution of some Mn atoms by Fe is given.
Abstract: In this work polycrystalline perovskite with composition La0.7Ca0.3Fe0.05Mn0.95O3 has been produced by standard ceramic method. A considerable change occurs in magnetic, transport and magnetoresistance properties with respect to the classic composition without Fe. The introduction of a different metal, Fe, in Mn-O layer causes a decrease of about 50 K in the value of TC. In the same way, a decrease of about 10–15% in the average magnetic moment measured at 1 T is also observed. On the other hand, the introduction of Fe does not cause any appreciable change in the value of the lattice parameter. This new compound presents 60% of giant magnetoresistance ratio at 200 K. Magnetization vs. temperature measurements in zero field cooling and field cooling show clear differences at applied fields below 80 kA m−1. Such a behavior, also observed in La0.7Ca0.3MnO3 sample, is not recognizable as a simple ferromagnetic one. A qualitative discussion of the effect in the magnetic and transport properties of these compounds, caused by the substitution of some Mn atoms by Fe is given.In this work polycrystalline perovskite with composition La0.7Ca0.3Fe0.05Mn0.95O3 has been produced by standard ceramic method. A considerable change occurs in magnetic, transport and magnetoresistance properties with respect to the classic composition without Fe. The introduction of a different metal, Fe, in Mn-O layer causes a decrease of about 50 K in the value of TC. In the same way, a decrease of about 10–15% in the average magnetic moment measured at 1 T is also observed. On the other hand, the introduction of Fe does not cause any appreciable change in the value of the lattice parameter. This new compound presents 60% of giant magnetoresistance ratio at 200 K. Magnetization vs. temperature measurements in zero field cooling and field cooling show clear differences at applied fields below 80 kA m−1. Such a behavior, also observed in La0.7Ca0.3MnO3 sample, is not recognizable as a simple ferromagnetic one. A qualitative discussion of the effect in the magnetic and transport properties of these compou...

Journal ArticleDOI
Dexin Li1, Yoshinori Haga1, H. Shida1, T. Suzuki1, Yong Seung Kwon, G Kido 
TL;DR: In this article, the authors report on the systematic magnetization measurements performed on the stoichiometric Gd monopnictides, ( = N, P, As, Sb, and Bi), at temperatures between 1.6 and 350 K in magnetic fields up to 42 T.
Abstract: We report on the systematic magnetization measurements performed on the stoichiometric Gd monopnictides, ( = N, P, As, Sb, and Bi), at temperatures between 1.6 and 350 K in magnetic fields up to 42 T. GdN shows the ferromagnetic behaviour with a Curie temperature . The other samples order antiferromagnetically at the Neel temperatures = 15.9, 18.7, 23.4, and 25.8 K for = P, As, Sb, and Bi, respectively. A spin - flop transition is observed at low temperature for except GdN. Based on molecular field approximation, the nearest-neighbour and next-nearest-neighbour exchange constants and of are calculated using the experimental data. Comparing with Eu monochalcogenides, the other group of S-state rare-earth compounds, the absolute values of and in are anomalously large, and the ferromagnetic RKKY interactions due to semimetallic carriers are very weak. These anomalous properties are discussed with a new theoretical model developed very recently by Kasuya.

Journal ArticleDOI
27 Jun 1997-Science
TL;DR: Magnetic domain behavior was imaged in calcium-doped lanthanum manganese trioxide films as mentioned in this paper, showing that magnetic domains behave differently at temperatures that are well below and near the Curie temperature T c.
Abstract: Magnetic domain behavior was imaged in calcium-doped lanthanum manganese trioxide films. Magnetic domains behave differently at temperatures that are well below and near the Curie temperature T c. At low temperatures the domains are very stable. As temperature rises toward T c, domain-domain interactions become weaker and domains become highly mobile and subject to merging and splitting, yet the domains are still traceable. The contrast (which is a measure of magnetization) and size of domains continuously reduce to zero. The temperature at which the domains disappear agrees with the T c obtained by a macroscopic magnetization measurement. Sample defects such as scratches tend to attract magnetic domains.

Journal ArticleDOI
TL;DR: In this paper, a sonochemical decomposition of solutions of volatile organic precursors, Fe20Ni80, Fe40Ni60, and Fe60Ni40, under an argon pressure of 100 to 150 kPa at 273 K is described.
Abstract: Nanosized amorphous alloy powders of Fe20Ni80, Fe40Ni60, and Fe60Ni40 were prepared by sonochemical decomposition of solutions of volatile organic precursors, Fe(CO)5 and Ni(CO)4 in decalin, under an argon pressure of 100 to 150 kPa at 273 K. Magnetic susceptibility of Fe40Ni60 and Fe60Ni40 indicates blocking temperatures of 35 K and a magnetic particle size of about 6 nm. Thermogravimetric measurements of Fe20Ni80 give Curie temperatures of 322 °C for amorphous and 550 °C for crystallized forms. Differential scanning calorimetry exhibits an endothermic transition at 335 °C from a combination of the magnetic phase transition and alloy crystallization. The Mossbauer spectrum of crystallized Fe20Ni80 shows a sextet pattern with a hyperfine field of 25.04 T.

Journal ArticleDOI
25 Jul 1997-Science
TL;DR: In this paper, the synthesis of and magneto-transport in the "colossal magnetoresistance" pyrochlore-structure compounds Tl2−xScxMn2O7 for 0 ≤ x ≤ 0.5 are reported.
Abstract: The synthesis of and magneto-transport in the “colossal magnetoresistance” (CMR) pyrochlore-structure compounds Tl2−xScxMn2O7for 0 ≤ x ≤ 0.5 are reported. The maximum resistivity (ρ) increases by 105 while the Curie temperature (Tc) decreases by only 25% between x = 0 and 0.4. For x = 0.2 to 0.3, the magnetoresistance at both high field (6 tesla) and low field (

Journal ArticleDOI
TL;DR: Petrophysical properties of drill core and drill cuttings samples from both bore holes of the German Continental Deep Drilling Program (KTB) measured at atmospheric pressure and room temperature in the field laboratory are presented, along with data of core samples measured at simulated in situ conditions by other laboratories as mentioned in this paper.
Abstract: Petrophysical properties of drill core and drill cuttings samples from both bore holes of the German Continental Deep Drilling Program (KTB) measured at atmospheric pressure and room temperature in the field laboratory are presented, along with data of core samples measured at simulated in situ conditions by other laboratories. Most of the petrophysical properties show a bimodal frequency distribution corresponding to the two main lithologies (gneiss and metabasite), except electrical resitivity and Th/U ratio which are lithology independent (monomodal distribution). Low resistivities are mainly associated with fractures zones enriched in fluids and graphite. The most abundant ferrimagnetic mineral is monoclinic pyrrhotite. Below 8600 m, hexagonal pyrrhotite with a Curie temperature of 260°C is the stable phase. Thus the Curie isotherm of the predominant pyrrhotite was reached (bottom hole temperature about 265°C). The highest values of magnetic susceptibility are linked with magnetite. Microcracks grow due to pressure and temperature release during core uplift. This process continues after recovery and is documented by the anelastic strain relaxation and acoustic emissions. The crystalline rocks exhibit marked reversible hydration swelling. Anisotropy of electrical resistivity, permeability, P and S wave velocity is reduced significantly by applying confining pressure, due to closing of microcracks. Fluids within the microcracks also reduce the P wave velocity anisotropy and P wave attenuation. Anisotropy and shear wave splitting observed in the field seismic experiments is caused by the foliation of rocks, as confirmed by laboratory measurements under simulated in situ conditions. The petrophysical studies provide evidence that microfracturing has an important influence on many physical rock properties in situ.

Journal ArticleDOI
TL;DR: In this article, the polar properties of the intermediate phase have been demonstrated and two solid-solid phase transitions at 210 and 323 K have been revealed and the pyridinium cation reorientation in all three phases characterized.
Abstract: Polycrystalline pyridinium periodate has been studied over a wide range of temperature by differential thermal analysis, proton nuclear magnetic resonance (NMR) spectra and relaxation and complex dielectric permittivity measurements. Two solid-solid phase transitions at 210 and 323 K have been revealed and the pyridinium cation reorientation in all three phases characterized. The polar properties of the intermediate phase have been demonstrated. The upper phase transition temperature appears to be the Curie point of a new ferroelectric compound.

Journal ArticleDOI
M. El-Shabasy1
TL;DR: In this paper, the electrical resistivity of Zn x Ni 1-x Fe 2 O 4 samples was studied as a function of temperature T c and composition x c, and the activation energy for the electric conduction in the paramagnetic region was found to be higher than that in the ferrimagnetic region.

Journal ArticleDOI
TL;DR: In this paper, the authors studied magnetic and magnetotransport properties of novel III-V diluted magnetic semiconductors, (Ga1−xMnx)As, which were grown on GaAs(001) substrates by low temperature molecular beam epitaxy.
Abstract: We have studied magnetic and magnetotransport properties of novel III-V diluted magnetic semiconductors, (Ga1−xMnx)As. The GaMnAs thin films were grown on GaAs(001) substrates by low temperature molecular beam epitaxy. We present magnetoresistance, extraordinary Hall effect, and M–H characteristics of two (Ga1−xMnx)As samples having different Mn content x.

Journal ArticleDOI
TL;DR: In this article, the annealing temperature dependence of the magnetic behavior was investigated by means of transmission 57 Fe Mossbauer spectrometry and DC magnetic measurements, in the range 50-700 nm.

Journal ArticleDOI
TL;DR: In this paper, a modified Faraday balance was used to measure the magnetization of a liquid Co 80 Pd 20 alloy undercooled by miniaturized electromagnetic levitation, and the effect was comparable to the behaviour of the corresponding solid phase.
Abstract: Miniaturized electromagnetic levitation has been used to undercool a liquid Co 80 Pd 20 alloy below the Curie temperature T C (l) = 1257 K of the liquid state. The magnetization of the undercooled liquid sample has been measured as a function of temperature using a modified Faraday balance. Below T C (l), the magnetization of the liquid metal shows a plateau in the weak external field of μ 0 H z = 5.6 mT. The effect is comparable to the behaviour of the corresponding solid phase, indicating the onset of spontaneous magnetization with ferromagnetic domains. T C (l) is about 20 K lower than the Curie temperature of the solid phase T C (s).