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[en] This paper presents the results of Curie temperature analyses, high temperature oxidation and electron microscope analyses of titano magnetite grains in volcanic rocks of Kenya. The rocks include basalts, trachytes, nephelinites, melanephelinites, olivine nephelinites,welded tuff and phonolites. The results based on the Curie temperatures and degree of high temperature oxidation of the rocks, age ranging from 1.5 to 13.5 My, may be classified into four broad groups.The correlation of measured Curie temperatures to compositional Curie appears to be significant (author)
[en] The magnetic susceptibility of a single crystal of high-purity gadolinium has been measured in the critical region with use of ac susceptibility methods. For reduced temperatures tapprox. >10/sup -3/, the data are described by a simple power law of the form chi = At-/sup γ/ with an exponent γ = 1.22(2) and a Curie temperature T/sub c/ = 293.51(3) K. For reduced temperatures tapprox. <10/sup -3/, the data cannot be described by a simple power law and indicate the possibility of a crossover to different critical behavior
[en] The tetragonal compound YbNiP has a low Curie temperature, T = 0.17 K, which can be further suppressed by substituting P by As and the rare case of a ferromagnetic quantum critical point occurs in the substitution series YbNi(PAs) at x 0.1. Here, we present the characterization of YbNi(PAs) single crystals with As concentrations 0 x 1 by electrical transport, heat capacity and magnetization measurements. We also discuss the effect on the magnetic ordering temperature of a substitution at the Yb site by hafnium and scandium.
[en] Here, using first-principles calculations, based on disordered local moment theory, combined with the self-interaction corrected local spin density approximation, we study magnetic interactions in GdX intermetallics for X = Cu, Zn, Ga, Cd, and Mg. Our predicted magnetic orders and ordering temperatures both at zero and other pressures agree well with experiments including the large increase in the Curie temperature of GdCd under pressure that is shown by our own experimental measurements. From our results it emerges that the Ruderman-Kittel-Kasuya-Yosida interaction on its own can not explain the observed behaviour under pressure, and that the magnetic ordering mechanism is strongly influenced by the occupations of both Gd and anion d-bands.
[en] Highlights: • The thermal-elastic properties are studied. • The influence of alloying elements on the Curie temperature is discussed. • The Young's moduli along different crystal directions are studied for CoCrFeMnNi.
[en] A-site K/Ce and B-site W/Cr co-substituted CaBi2Nb2O9 ceramics were synthesized by a conventional solid-state reaction process. The structures, piezoelectricity and electrical conduction behaviors were investigated in detail. The Ca0.95(K1/2Ce1/2)0.05Bi2Nb1.99(W2/3Cr1/3)0.01O9 ceramic exhibited best properties with a high d33 (piezoelectric coefficient) of ~ 18.4 pC/N and a high TC (Curie temperature) of ~ 917 °C. In addition, the ceramic displayed an excellent thermal stability performance such that d33 remained 94% of its initial value even after annealing at 900 °C for 2 h. The planar electromechanical coupling factor was observed to increase from 9.00% at room temperature to 15.24% at 600 °C. Furthermore, a high electrical resistivity of 1.16 × 105 Ω cm at 600 °C and a good fatigue property were also achieved with this composition. The Ca0.95(K1/2Ce1/2)0.05Bi2Nb1.99(W2/3Cr1/3)0.01O9 ceramic was found to be a promising candidate for high-temperature piezoelectric applications.
[en] A number of anomalous effects occurring at the compensation and Curie points of ferrites are explained on the basis of the concept of unidirectional exchange anisotropy. Among these are the violation of 'evennies' for the magnetostrictive, magnetoresistive, and magnetocaloric effects, the antiferromagnetic paraprocess, and some other phenomena. Based on the analysis of these effects, a piezomagnetic effect is predicted to occur in 'weak-sublattice' ferrimagnets. (methodological notes)
[en] The 1/3 magnetization step is an important feature in spin frustrated Ca3Co2O6 and can be modified by chemical doping. Taking Ca3Co2−xMnxO6 as an example, we find that as Mn-doping reaches x=0.33–0.35, the field-induced 1/3 magnetization step, which is a manifestation of the partially disordered antiferromagnetic state, tends to vanish. The critical value of x=0.33–0.35 is consistent with the composition where the paramagnetic Curie temperature changes its sign from positive to negative, showing a correlation between the 1/3 magnetization step and the magnetic exchange interaction. - Highlights: • As x=0.33–0.35, the field-induced 1/3 magnetization step tends to vanish. • As x=0.33–0.35, the paramagnetic Curie temperature becomes negative. • The 1/3 magnetization step correlates with magnetic exchange interaction