Papers by Keyword: Curie Temperature

Abstract: Mn_1.25Fe_0.65-xSn_xP_0.50Si_0.50 (0, 0.02, 0.04, 0.05, 0.06, 0.08, 0.09, 0.10, 0.20) series compounds were prepared by mechanical alloying and solid-phase sintering, and their mechanical and magnetic properties were studied. The XRD measurement results show that all the compounds crystalize in Fe₂P hexagonal structures, with a space group of P-62m. With the increase in Sn content, the compressive strength is significantly improved, the Curie temperature of the compound gradually decreases, and the nature of magnetic transition is tuned from a weak to strong first-order one, which is confirmed by the increase of thermal hysteresis of the compounds. The maximum magnetic entropy change of the compound increases from 9.3 J/kg·K at x = 0 to 17.2 J/kg·K at x = 0.04 under a magnetic field change of 0 - 3 T.

Abstract: The influence of the cooling rate during sintering of lithium-titanium-zinc-manganese spinel ferrite on its structural, magnetic and electric characteristics was studied. The ferrite was sintered in air at 1283 K for 120 min. Cooling rates were 0.06 K/s and 7.8 K/s. It was established that the observed changes in the characteristics when using slow and quenching cooling are due to the different levels of the near-surface ferrite layers oxidation. For quench ferrite, the Curie temperature of 530 K, the activation energy of electrical conductivity of 0.35 eV in the bulk of the samples, and the magnetic anisotropy constant of 2.6·10^-3 J/m³ (at 300 K) were obtained. Slowly cooled ferrite was characterized by higher values of Curie temperature (560 K), the magnetic anisotropy constant (2.9·10^-3 J/m³), and the activation energy of electrical conductivity (0.80 eV).

Abstract: We reported the structural, magnetic and magenetocaloric properties of Mn_1.25Fe_0.75P_{0. 50}Si_0.50B_x (x = 0.01, 0.02 and 0.04) X-ray diffraction patterns show that all compounds crystallize in the hexagonal Fe₂P-type crystal structure. Lattice parameter a increases while c decreases with increasing B contents. The Curie temperature of the compounds have been determined, the values are 219, 268 and 323.2 K for x = 0.01, 0.02, 0.04, respectively. The maximum magnetic entropy changes in a field change of 0~1.5 T are 6.1, 5.3 and 3.5J/kg·K for x = 0.01, 0.02 and 0.04, respectively.

Abstract: The effect of Fe-substitution at the Mn-site in La_0.7Ca_0.3Mn_1-xFe_xO₃ (x = 0, 0.01, 0.03 and 0.05) on its structure, electrical and magnetic properties has been studied. These properties were investigated via X-ray diffraction (XRD) analysis, temperature-dependent resistance measurements and temperature-dependent AC magnetic susceptibility measurements. XRD analysis showed all samples are single phase materials. Temperature dependent resistance measurements between 30–300 K showed all samples to undergo insulator-metal transition as temperature decreases. Increase in Fe doping for x = 0, 0.01, 0.03 and 0.05 caused the transition temperature T_IM to decrease from 257 K, 244 K, 205 K and 162 K respectively. The magnetic susceptibility measurements showed the samples to exhibit paramagnetic to ferromagnetic transition as temperature decreased. Increase in Fe substitution x at the Mn-site progressively decreased the Curie temperature T_C from 250 K at x = 0 to 170 K at x = 0.05.

Abstract: Herein, the spinel Co_1-xZn_xFe₂O₄ (x = 0.0, 0.2, 0.4 and 0.6) powder samples have been prepared by the solid-state reaction method. We have carried out the measurements of crystal structure, element analysis, material characterization, magnetic property and Curie temperature using the X-ray diffraction (XRD), Energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer, and the first-principles calculations within the framework of the density functional theory (DFT). The EDS measurement indicates that the Co_1-xZn_xFe₂O₄ powder samples have been successfully synthesized and exhibited the cubic spinel structures. Both the lattice constant and crystallite size increase with the Zn concentration due to the larger ionic radius of Zn²⁺ ion than the Co²⁺ ion. The concentration ratio of the Co²⁺ and Co³⁺ ions can be predicted by the distribution of cations between the A and B sites by the XPS measurement. For the magnetic properties, the residual magnetization, coercivity and Curie temperature decrease monotonically as the Zn concentration increases, while the saturation magnetization initially increases and then decreases at the room temperature. For the Co_0.8Zn_0.2Fe₂O₄ sample, the magnetic saturation reaches the maximum value of 62.98 Am²kg^-1, due to a large amount of the Co³⁺ ions. The adequate replacement of Zn ion for the Co site can improve the magnetic properties of spinel Co_1-xZn_xFe₂O₄ powders, and effectively regulates the Curie temperature.

Abstract: Ferroelectric ceramic solid solutions Li_xNa_1-xTa_yNb_1-yO₃ (х = 0.17; у = 0 – 0.5) with the perovskite structure have been obtained by the thermobaric synthesis method. Particularities of their microstructure, elastic properties, electrical conductivity and permittivity have been researched. It has been established that an increase in the thermobaric synthesis temperature leads to a decrease in the Young’s modulus value. Specific static conductivity values have been determined; charge carrier activation enthalpies Н_а have been calculated. The Curie temperature of the samples has been determined to decrease with an increase in tantalum content. A Ferroelectric ceramic solid solution Li_0.17Na_0.83Ta_0.1Nb_0.9O₃ was shown to undergo four structure phase transitions in the temperature range 300-820 К. A Li_0.17Na_0.83Ta_0.1Nb_0.9O₃ has been shown to be a high temperature superionic. Possible mechanisms of the detected phenomena are discussed.

Abstract: (Fe,Ni)₂(P,Si) compounds were synthesized and characterized. Ni substitution in Fe_1.95-xNi_xP_0.7Si_0.3 is found to favor the formation of Fe₂P-type hexagonal structure. The samples appear nearly single phase. Powder oriented in the magnetic field shows a pronounced uniaxial magnetic anisotropy with c axis as the easy axis. Magnetization measurements carried out along and perpendicular to the c crystal axis demonstrate a significant magnetic anisotropy, making these materials potential candidates for permanent magnet applications. We found that (Fe,Ni)₂(P,Si) compound has no remanent magnetic field and coercivity, but it has a large magnetocrystalline anisotropy at room temperature. Therefore, doping Fe₂P type compounds with a small amount of Ni and Si may be a promising way to create new materials with large magnetocrystalline anisotropy at room temperature, and thus rare-earth free permanent magnet.

Abstract: This paper reports the effect of Cu doping in first order phase transition material Mn_1.28Fe_0.67P_0.48Si_0.52 on its phase structure, magnetocaloric effect and mechanical properties. The results of XRD, SEM and EDS analysis show that the Mn_1.28Fe_0.67P_0.48Si_0.52 in this composite forms Fe₂P hexagonal structure and the space group is P-62m;Most of Cu exists as a simple substance, and a small amount of Cu and Mn form a solid solution. When the mass ratio of Cu reaches 10:4, the (Mn,Fe)₃Si phase appears in Mn_1.28Fe_0.67P_0.48Si_0.52. The magnetic measurement results show that the saturation magnetization of Mn_1.28Fe_0.67P_0.48Si_0.52 after Cu doping has no obvious change, the Curie temperature decreases, and the thermal hysteresis increases. The maximum magnetic entropy change becomes smaller as the Cu content increases. Under a 1.5 T external magnetic field, the maximum magnetic entropy ΔS_m of the composite decreases rapidly from 11 J/kg·K at x = 0 to 4 J/kg·K at x = 5,the half width of the magnetic entropy change gradually increases. The Vickers hardness of the composite is reduced, the compressive strength has been greatly improved, and the mechanical properties have been significantly enhanced after Cu doping.

Abstract: Single crystals of lead germanate are obtained by the Czochralski technique. The dimensions of hexagonally shaped crystals are up to 25 × 25 × 5 mm³. According to X-ray diffraction measurements the grown crystals respond to lead germanate Pb₅Ge₃O₁₁ structure. Curie temperature was also measured.

Abstract: To understand the phase composition and improve the magnetic performances of Ce₂Fe₁₄B-type alloys, the ribbons of Ce₁₆Fe_95-xCo_xB₈ (x=0-4.0) were prepared by melt-spinning at a quench wheel velocity of 40 m/s. The phase composition and magnetic properties of Ce₁₆Fe_95-xCo_xB₈ (x=0-4.0) alloys were investigated. XRD results indicated that the main phase existed in the as-spun ribbons is Ce₂Fe₁₄B. The amorphous formation ability and thermal stability of as-spun ribbons were enhanced by trace cobalt addition. Co-doped samples had higher Curie temperature compared with bare Ce₂Fe₁₄B, which signified that Co atoms could substitute for Fe directly into Ce₂Fe₁₄B phase. The corrosion potential of alloys from-1089mV (vs. SCE) to-1077mV (vs. SCE) which indicated that the Co-doped provided better corrosion protection properties for the Ce-Fe-B magnet compared with bare substrate.