共查询到20条相似文献,搜索用时 0 毫秒
1.
2.
The magnetic properties and magnetocaloric effect in Fe4MnSi3Bx compounds with x=0, 0.05, 0.10, 0.15, 0.20, 0.25 have been investigated. X-ray diffraction study shows that all these compounds investigated crystallize in the Mn5Si3-type structure with space group P63/mcm. Boron insertion in the host ternary silicide Fe4MnSi3 does not change the crystal symmetry, only leads to an increase of the lattice parameters, indicating the B atoms entered the interstitial sites. With increasing B content, the Curie temperature shifts to higher temperatures. The maximal magnetic-entropy changes of the Fe4MnSi3Bx compounds with x=0, 0.10 and 0.20 are about 1.8 J/(kg·K), 1.8~J/(kg·K) and 1.6~J/(kg·K), respectively, for a field change from 0 to 1.5 T. 相似文献
3.
The magnetic properties and magnetocaloric effect in Fe4MnSi3Bx compounds with x=0, 0.05, 0.10, 0.15, 0.20, 0.25 have been investigated. X-ray diffraction study shows that all these compounds investigated crystallize in the Mn5Si3-type structure with space group P63/mcm. Boron insertion in the host ternary silicide Fe4MnSi3 does not change the crystal symmetry, only leads to an increase of the lattice parameters, indicating the B atoms entered the interstitial sites. With increasing B content, the Curie tem... 相似文献
4.
Seda Aksoy Atila Yucel Yalcin Elerman Thorsten Krenke Mehmet Acet Xavier Moya Lluís Maosa 《Journal of Alloys and Compounds》2008,460(1-2):94-98
Gd5Si2Ge2 was alloyed with varying amounts of Ga to study its influence on the giant magnetocaloric effect. Investigations on Gd5(Si2−xGe2−x)Ga2x with 2x = 0.03, 0.05 and 0.13 were carried out using X-ray powder diffraction, temperature and magnetic field dependent magnetization measurements, and differential scanning calorimetry. We observe that as the Ga content increases, the temperature stability range of the monoclinic phase narrows, and the orthorhombic structure gains stability. This is expected to be related to the decrease in the (Si/Ge)(Si/Ge) bond distance in the monoclinic phase. The maximum entropy change for the parent compound at 270 K was found to be 9.8 J kg−1 K−1 in an applied field of 5 T. For 2x = 0.03, this value reduces to 8.5 J kg−1 K−1, and the temperature corresponding to the maximum entropy change shifts marginally to 278 K. For other 2x values, the maximum entropy change further decreases. 相似文献
5.
Gd5Si2Ge2 parent compounds were alloyed with Mn in order to understand the underlying relation between the structural phases and the magnetic behavior of the pseudo ternary compounds formed. The alloying mechanism in Gd5Si2Ge2 causes simultaneous substitution of the nonmagnetic Si and Ge atoms from the (Si + Ge) sublattice in equal amounts. No subsequent heat treatment was made on alloyed compounds. X-ray powder diffraction, magnetization versus temperature and isothermal magnetization measurements were carried out. X- ray diffraction patterns were used to qualitatively determine the existence of different structural phases in the alloys. It was observed that the starting, as-melted alloy with z = 0 has Gd5Si4-type orthorhombic structure at room temperature with traces of 1:1 stoichiometry phase which transforms totally to a Gd5Si2Ge2-type monoclinic phase when heat treated. Similarly, increase in the Mn content leads to an increase in the monoclinic phase content of the originally orthorhombic compounds. Curie temperatures were determined from M(T) measurements and the magnetocaloric characterization was made using M(H) measurements by plotting the magnetic entropy change values against temperature. No giant magnetocaloric effect was observed for non heat treated samples. 相似文献
6.
《Intermetallics》2016
The structural, magnetic and magnetocaloric properties of the polycrystalline compound HoMn2Si2 have been studied. The temperature variation of magnetization and heat capacity show that below room temperature the compound under goes multiple magnetic transitions, at about 80, 15 and 3.5 K respectively. Moreover, the presence of the interesting thermomagnetic irreversibility in HoMn2Si2 is detected in the magnetization versus temperature plot, which can be ascribed to the narrow domain wall pinning effect. A broad and asymmetric peak is observed for the MCE response which might suggest the underlying first-order nature of the transition and/or the spin fluctuations of the Mn subsystem. The density of states N(EF) at the Fermi level and the Debye temperature have been determined and analyzed. Large magnetocaloric effect (ΔSM = −9 J/kg-K for a field change of 5 T around 9 K) suggest that this material is suitable for the low temperature magnetic refrigeration. 相似文献
7.
8.
The Ce2Fe17−xMnx (x = 0-2) compounds demonstrate a complex temperature dependence of the magnetocaloric effect MCE, which is inverse in a narrow temperature interval just below Néel temperature TN and normal at higher or lower temperatures. The normal MCE exhibits two peaks in the vicinity of temperatures of ferromagnetic ordering ΘT and TN for compositions x = 0-0.35, 1.3-2 or one peak near TN for antiferromagnets with x = 0.5-1. The maximal change of the peak entropy −SM is about 3 J/kg K in a field of 5 T for the compounds with x = 0-0.5 at T ∼230 K close to TN. The drastic decrease of the MCE, by half, in the Ce2Fe17−xMnx system is traceable to a decrease of the spontaneous magnetization and the helical type of magnetic states in the compounds. 相似文献
9.
Some recent data on the magnetocaloric effect in lanthanide materials are reviewed. It is shown that the variation of interaction exchange energy, taking place under the effect of a magnetic field in the vicinity of the phase transformation, provides a significant contribution to the change of magnetic entropy. New theoretical relations for the magnetocaloric effect at the phase transition point of magnetic materials are discussed. Physical mechanisms of heat generation in magnetic materials under adiabatic conditions are analyzed. 相似文献
10.
11.
采用高分子网络法制备混合纳米粉体,研究稀土氧化物Y2O3和Pr6O11加入量对Al2O3陶瓷相对密度和热导率的影响。采用阿基米德方法测定样品的体积密度,利用激光脉冲法测量试样的热扩散率并计算得出热导率。结果表明:两种添加剂都可以降低Al2O3陶瓷的烧结温度,提高Al2O3陶瓷的热导率,其中Y2O3的促进作用较强;当保温时间相同、烧结温度为1 500~1 650℃时,Al2O3陶瓷的相对密度和热导率都随烧结温度的升高而增大;当烧结温度相同、保温时间为30~120 min时,Al2O3陶瓷的相对密度和热导率也随保温时间的延长而增大。 相似文献
12.
Tb3Rh exhibits a giant magnetocaloric effect (GMCE) around ordering temperature of 88 K. The maximum magnetic entropy change ΔSm obtained at 2 T, 3 T, 5 T and 7 T amounts −11.6 J/(K kg), −14 J/(K kg), −17.9 J/(K kg) and −21 J/(K kg) respectively. The origin of an enhanced MCE is related to a first-order magnetic transition. Magnetic frustration and short range correlation are very important in understanding the properties of Tb3Rh. 相似文献
13.
In this paper, the magnetic properties and magnetocaloric effect (MCE) of La0.7(Ca1−xAgx)0.3MnO3 (x = 0, 0.1, 0.2, 0.7, and 1) powder samples are reported. Our polycrystalline compounds were synthesized using the solid state reaction method at high temperature. Magnetization measurements versus temperature showed that all our samples exhibited a paramagnetic to ferromagnetic transition with decreasing temperature. The Curie temperature, TC, has been found to increase from ∼250 K for x = 0-270 K for x = 1. Ag doping weakens the first order phase transition, and at higher Ag doping, the phase transition is of second order. For the La0.7(Ca0.27Ag0.03)MnO3 composition, the maxima of the magnetic entropy changes from the applied magnetic field (ΔSM) at 2 and 5 T are about 4.5 and 7.75 J/kg K, respectively, at the Curie temperature of ∼263 K. The relative cooling power (RCP) values without hysteresis loss are about 102 and 271 J/kg for the applied fields of 2 and 5 T, respectively. Due to the large ΔSM, large RCP, and high Curie temperature, La0.7(Ca0.27Ag0.03)MnO3 is promising for application in potential magnetic refrigeration near room temperature. 相似文献
14.
15.
The LaFe11.6Si1.4 compounds are prepared by arc-melting and then annealed at different high temperatures from 1323 K(5 h) to 1623 K(2 h). The powder X-ray diffraction and metallographic microscopy show that 1423 K and 1523 K are two curial temperatures, at which large amount of 1:13 phase begins to form and the most amount of 1:13 phase is obtained, respectively. With annealing temperature increasing to 1573 K and 1623 K, a new phase of La5Si3 is detected in LaFe11.6Si1.4 compound. According to the DSC curve of as-cast LaFe11.6Si1.4 compound and the X-ray patterns of annealed LaFe11.6Si1.4 compounds, the high-temperature phase transition process is analyzed. For studying the influence of different high-temperature and short-time annealing on the Curie temperature, thermal and magnetic hysteresis, magnetocaloric effect of LaFe11.6Si1.4 compound annealed at different temperatures are also investigated. 相似文献
16.
18.
Jo Chol-Lyong Xia Lei Ding Ding Dong Yuan-Da Ekoko Gracien 《Journal of Alloys and Compounds》2008,458(1-2):18-21
The structure and magnetic entropy changes in melt-spun and annealed LaFe11.8−xCoxSi1.2 (x = 0, 0.4 and 0.8) ribbons have been investigated. It is found that the value of Tc can be increased continuously up to 290 K for x = 0.8 and the phase transition, at Tc from paramagnetic to ferromagnetic, is changed from first- to second-order due to Co substitution. Large values of the magnetic entropy change are 31 and 13.5 J/kg K in the magnetic field change from 0 to 5 T at 201 K for the LaFe11.8Si1.2 and at 290 K for the LaFe11Co0.8Si1.2 ribbons, respectively. The magnetic entropy change in the LaFe11Co0.8Si1.2 ribbons is higher than that reported in the bulk counterpart and that of conventional MCE materials, such as pure Gd. The enhanced magnetic entropy change of ribbons compared to bulk counterpart is attributed to a more uniform microstructure and element distribution resulting from the high cooling rate by melt-spinning. 相似文献
19.
采用工业纯原料感应熔炼制备出公斤级La_(0.6)Pr_(0.4)Fe_(11.4)Si_(1.6)B_(0.2)合金,经退火后通过吸氢处理提高其居里温度到室温附近。研究了在1373~1473 K温度下经不同时间和温度退火对合金微观组织结构的影响。实验发现在1473 K经30 h退火样品的居里温度为202 K,在0~1.5 T变化磁场下的最大磁熵变达8.1~8.6 J/kg·K。在0.13 MPa氢气压力下,经553 K吸氢5 h氢化处理合金的居里温度为320 K,最大磁熵变达7.7~8.0 J/kg·K。 相似文献
20.
Neutron diffraction and magnetization measurements have been performed on the Tb5Si3 compound (hexagonal Mn5Si3-type, hP16, P63/mcm) to understand its magnetic structure and magnetic properties. The temperature-dependent neutron diffraction results prove that this intermetallic phase shows a complex flat spiral magnetic ordering, presenting three subsequent changes in magnetization at on cooling. However, the magnetization data depict two transitions at 72 K (TN1) and 55 K (TN2). The extended temperature range between and over which the neutron diffraction patterns slowly evolve might correspond to the high-temperature antiferromagnetic transition at TN1 and low-temperature antiferromagnetic transition at TN2 of the magnetic data. Between Tb5Si3 shows a flat spiral antiferromagnetic ordering with a propagation vector K1 = [0,0, ±1/4]; then, between the flat spiral type ordering is conserved, but by two coexisting propagation vectors K1 = [0,0, ±1/4] and K2 = [0,0, ±0.4644(3)]. The terbium magnetic moments arrange in the XY(ab) plane of the unit cell. Below the magnetic component with K1 = [0,0, ±1/4] vanishes and magnetic structure of Tb5Si3 is a flat spiral with K2 = [0,0, ±0.4644(3)], only. Low field magnetization measurements confirm the occurrence of complex, multiple magnetic transitions. The field dependence of the magnetization indicates a metamagnetic transition at a critical field of 3 T. 相似文献