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The structural and magnetocaloric properties of Mn1.35Fe0.65P1-xSix compounds are investigated. The Sisubstituted compounds, Mn1.35Fe0.65P1-xSix with x = 0.52, 0.54, 0.55, 0.56, and 0.57, are prepared by high-energy ball milling and the solid-state reaction. The X-ray diffraction shows that the compounds crystallize into the Fe2P-type hexagonal structure with space group P62m. The magnetic measurements show that the Curie temperature of the compound increases from 253 K for x = 0.52 to 296 K for x = 0.56. The isothermal magnetic-entropy change of the Mn1.35Fe0.65P1-xSix compound decreases with the Si content increasing. The maximal value of the magnetic-entropy change is about 7.0 J/kg·K in the Mn1.35Fe0.65P0.48Si0.52 compound with a field change of 1.5 T. The compound quenched in water possesses a larger magnetic entropy change and a smaller thermal hysteresis than the non-quenched samples. The thermal hysteresis of the compound is less than 3.5 K. The maximum adiabatic temperature change is about 1.4 K in the Mn1.35Fe0.65P0.45Si0.55 compound with a field change of 1.48 T. [ABSTRACT FROM AUTHOR]

Abstract: The structural and magnetic properties of MnCo1−x V x Ge (x =0.00, 0.02, 0.04, 0.06, 0.08, 0.10, 0.20 and 0.30) compounds were investigated by means of X-ray diffraction, scanning electron microscopy and magnetization measurements. The MnCo1−x V x Ge compounds crystallize in the orthorhombic TiNiSi-type crystal structure for x ≤0.02 and in the hexagonal Ni2In-type structure for x >0.02. The magnetization measurements show that the MnCo1−x V x Ge compounds exhibit a complex magnetic behavior. The Curie temperature can be tuned from 360K to 148K by increasing x. The maximal magnetic-entropy change is 3.9J/kgK for x =0.06 at a field change from 0 to 1.5T at about 265K. [Copyright &y& Elsevier]

Abstract: We have performed powder X-ray-diffraction measurements on in fields up to 5T in the temperature range 8–310K. The compound which has the hexagonal type of structure shows a field-induced isostructural phase transition. We found that the cell volume decreases slightly and continuously with increasing magnetic field, although the lattice parameter ratio c/a drastically changes. A tentative analysis of the dependence of the lattice parameters on the magnetization has been carried out using the extended Bean–Rodbell model. [Copyright &y& Elsevier]

The structural and magnetic properties of MnFe1-xCox Ge compounds with x = 0,0.1,0.2,0.3,0.4,0.5,0.6,0.7,0.8,0.85,0.9, and 1.0 were investigated by means of X-ray diffraction (XRD) and magnetization measurements. XRD shows that the MnFe1-x Cox Ge compounds crystallize in the hexagonal Ni2In-type crystal structure for x ≤ 0.8 and in the orthorhombic NiTiSi-type structure for x > 0.8. The magnetization measurements show that the MnFe1-x Cox Ge compounds exhibit a complex magnetic behavior. The Curie temperature increases with increasing of x. The saturation magnetization of the compounds with Ni2In type structure increase with increasing of x and the saturation of the magnetization in the NiTiSi-type structure also increases with increasing x. We investigated the magnetocaloric effects in these compounds by means of magnetization measurements. The maximum magnetic-entropy change observed in these compounds reaches 9 J/kgK for x = 0.8 in a field change from 0 to 5 T at around 289 K. [ABSTRACT FROM AUTHOR]

We have studied the magnetocaloric effect in MnFe(P,Si,Ge) compounds. The structural properties of the compounds were determined by x-ray diffraction. The homogeneity and the stoichiometry of the compounds were checked by electron probe microanalysis. The Curie temperature is found to be near room temperature. Specific-heat measurements made on these compounds show a first-order ferromagnetic—paramagnetic phase transition. The magnetocaloric effect derived from magnetization data shows that this effect in the MnFe(P,Si,Ge) compounds is as large as that in Gd-based compounds and MnFeP1-xAsx compounds. This means that we have succeeded in totally replacing As by (Ge,Si) in the latter compounds without losing the favorable magnetic properties. The upshot is that we have found relatively low cost and nontoxic materials for room-temperature cooling applications. [ABSTRACT FROM AUTHOR]

High field X-ray powder diffraction and magnetization measurements were carried out for MnFePGe in order to investigate the magnetic field effect on the structural property. A field-induced anisotropic lattice deformation was observed, accompanied by the metamagnetic transition from the paramagnetic to the ferromagnetic states in the vicinity of the Curie temperature of 285 K. In this deformation at 280 K, the lattice parameter a expands by 1.2 % whereas the parameter c contracts by 2.7 %. [ABSTRACT FROM AUTHOR]

The structural and magnetic properties of Sm2Co17-xCrx (0≤x≤3.0) compounds have been investigated by means of X-ray diffraction and magnetization measurements. The powder X-ray diffraction patterns show that all samples crystallize as a single phase with the rhombohedral Th2Zn17-type structure. The lattice parameters a and V increase monotonically with increasing Cr content, but the lattice parameter c increases very slowly with increasing Cr content. The X-ray diffraction patterns of the aligned powder of the samples have confirmed that all the compounds investigated have uniaxial anisotropy. The Curie temperature of the compounds decreases rapidly the spontaneous magnetization M0, the anisotropy field Ba, and the anisotropy constant K1 of Sm2Co17-xCrx (0≤x≤3.0) compounds decrease strongly with increasing Cr content. [Copyright &y& Elsevier]

Fe2MnSi1−xGex (x=0, 0.2, 0.4, 0.5, 0.6, 0.8, 1) compounds were prepared by a mechanically activated solid-state diffusion method. Both X-ray diffraction and differential scanning calorimetry evidenced the presence of an amorphous phase after 10 h of milling. The X-ray data reveal that in the high-temperature annealing the single D03-type phase can be retained up to 50% substitution of Ge for Si in Fe2MnSi. A metastable D03 phase is obtained after crystallization of the as-milled amorphous compounds with x>0.5. High-temperature annealing transforms the low-temperature D03 phase into a single D019 phase (x=1) or a mixture of D03 and D019 phase (x=0.6 and 0.8). Low-field thermomagnetic measurements show a moderately sharp ferromagnetic-paramagnetic transition, which becomes enormously broad in higher magnetic fields. The Curie temperature is significantly enhanced when going from the D03 phase to the D019 phase. Neither a magnetic-field-induced transition nor a reversible structural transition is observed throughout this compound series. The magnetocaloric effect associated with the magnetic transition is small. [Copyright &y& Elsevier]

We synthesized for the first time the intermetallic compound Fe2MnGe. To avoid preferential evaporation of volatile components we exploited mechanical alloying. Amorphous Fe2MnGe alloy powder was prepared by planetary ball milling elemental starting materials. The amorphous-to-crystalline transition was studied by means of differential scanning calorimetry (DSC) and X-ray diffraction (XRD). A cubic D03 phase is formed at low temperature and transforms to a high-temperature hexagonal D019 phase. The apparent activation energy was determined by means of the Kissinger method. [Copyright &y& Elsevier]

Abstract: The phase formation and the magnetic properties of YFe12− x Nb x compounds have been investigated by means of X-ray diffraction and magnetization measurements. The powder X-ray diffraction patterns show that all compounds investigated crystallize single phase in the tetragonal ThMn12-type of structure. The lattice parameters and the unit-cell volume increase slightly with increasing Nb content, but the Curie temperature does not change. The X-ray-diffraction patterns of aligned powders of the samples show that all the compounds investigated have uniaxial anisotropy at room temperature. At 1.5K, the spontaneous magnetization, the anisotropy field and the anisotropy constant K 1 decrease with increasing Nb content. [Copyright &y& Elsevier]

We have studied the magnetic properties of Mn5Ge3−xSbx compounds with x=0, 0.1, 0.2 and 0.3 by means of magnetisation measurements at different temperatures and fields up to 5 T. The compounds crystallize in the hexagonal Mn5Si3-type structure with space group P63/mcm. The compounds show enhanced Curie temperatures but decreasing average magnetic Mn moments with increasing Sb content. The magnetic entropy changes in these compounds are determined from the temperature and field dependence of the magnetisation using the thermodynamic Maxwell relation. Mn5Ge3 exhibits considerably large magnetic entropy changes that are comparable with that of Gd metal. The Sb substitution has two kinds of effects on the magnetocaloric effect (MCE) of Mn5Ge3−xSbx. One is the magnetic entropy change that decreases with increasing Sb content, the other is the MCE peak that becomes broadened. [Copyright &y& Elsevier]

Nanocrystalline Ca-doped CeB 6 powders have been synthesized via a solid-state reaction of CaO and CeO 2 with NaBH 4 under a vacuum condition. The Ca doping effects on phase composition, grain morphology and optical absorption properties of nanocrystalline CeB 6 were investigated. As a result, all the synthesized nanocrystalline hexaborides are composed by single phase of CsCl -type structure. The grain size and morphology are very sensitive to the reaction temperature. The optical absorption result indicates that the absorption valley of nanocrystalline CeB 6 shows a red-shift from 619 nm to 685 nm with increasing Ca doping content, which means the tunable optical absorption of nanocrystalline Ca-doped CeB 6 . In addition, a first-principles calculation has been used to reveal the origin of the tunable optical properties. It is found that Ca doping reduces the total kinetic energy of the electrons of CeB 6 and leads to the absorption valleys shift to longer wavelength direction. [ABSTRACT FROM AUTHOR]

Herein, we report the synthesis of nanocrystalline La 1-x Ca x B 6 (0 ≤ x ≤ 1) hexaboride powders by solid-state reaction and their subsequent consolidation via spark plasma sintering. The structural, magnetic and thermionic emission properties of La 1-x Ca x B 6 hexaboride are investigated. All of the synthesized nanocrystalline hexaboride powders are single phase with the CsCl -type structure and no ferromagnetic impurity phases have been detected from X-ray diffraction. Magnetic measurements show that weak ferromagnetism at room temperature is found in nanocrystalline La 1-x Ca x B 6 hexaboride powders, and the magnetism was attributed to the presence of the intrinsic defects, based on the data of the HRTEM. Thermionic emission measurements indicate that the maximum emission intensity for bulk La 0.4 Ca 0.6 B 6 at 1873 K reached 20.02 A/cm 2 , which is more than three times higher as compared to bulk CaB 6 (∼6.04 A/cm 2 ). When the La doping was increased to 40 at%, the work function of CaB 6 decreased from 2.95 to 2.76 eV, indicating an improvement in the thermionic emission performance. Therefore, the quasibinary La 1-x Ca x B 6 hexaboride may have an application as a promising cathode. [ABSTRACT FROM AUTHOR]

Crystalline PrB 6 nanoparticles with the sizes ranging from 100~300 nm were synthesized by a solid-state reaction of Pr 6 O 11 /PrCl 3 and NaBH 4 in the temperature range of 1100~1200 °C. The crystal structure, component and morphology of the PrB 6 nanoparticles were characterized by using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show that the particles crystallize in the CsCl structure type. The selected-area electron diffraction patterns reveal the particles have single-crystalline nature. XANES study shows that the Pr atoms in the PrB 6 particles are in trivalent state even if the Pr atoms possess the mixed valence state in the raw material Pr 6 O 11 . [ABSTRACT FROM AUTHOR]

Submicron crystalline LaB 6 has been successfully synthesized by a solid-state reaction of La 2 O 3 with NaBH 4 at 1200 °C. The effects of reaction temperature on the crystal structure, grain size and morphology were investigated by X-ray diffraction, scanning electron microscope and transmission electron microscope. It is found that when the reaction temperature is in the range of 1000–1100 °C, there are ultrafine nanoparticles and nanocrystals that coexist. When the reaction temperature elevated to 1200 °C, the grain morphology transformed from ultrafine nanoparticle to submicron crystals completely. High resolution transmission electron microscope images fully confirm the formation of LaB 6 cubic structure. [ABSTRACT FROM AUTHOR]

Abstract: The influences of Mn/Fe ratio on the structural, magnetic and magnetocaloric properties of Mn2−x Fe x P0.6Si0.25Ge0.15 compounds with x =0.7, 0.8, 0.9, and 1.0 have been investigated by means of X-ray diffraction and magnetization measurements. We find that the impurity phase (Mn,Fe)3(Si,Ge)1 disappears in the samples with higher Mn/Fe ratios. The change of Mn/Fe ratio induces a modification of the lattice dimension, which further leads to a change in the transition temperature. The observation of large thermal hysteresis indicates the occurrence of first-order phase transitions in all the studied samples. However, some characteristics of second-order phase transition have been observed in the isothermal magnetization curves and the isothermal entropy change (ΔS T ) curves for the samples with x =0.7 and 0.8. The maximum values of ∣ΔS T ∣ under a field change from 0 to 9T are found to be 8.9, 14.9, 22.2 and 22.4J/kgK for x =0.7, 0.8, 0.9 and 1.0, respectively. [Copyright &y& Elsevier]

Abstract: The effects of substitution of Co for Fe on the magnetic and magnetocaloric properties of La0.8Ce0.2Fe11.4− x Co x Si1.6 (0, 0.2, 0.4, 0.6, 0.8 and 1.0) compounds have been investigated. X-ray diffraction shows that all compounds crystallize in the NaZn13-type structure. Magnetic measurements show that the Curie temperature (T C) can be tuned between 184 and 294K by changing the Co content from 0 to 1. A field-induced methamagnetic transition occurs in samples with x=0, 0.2 and 0.4. The magnetic entropy changes of the compounds have been determined from the isothermal magnetization measurements by using the Maxwell relation. [Copyright &y& Elsevier]

Abstract: We have studied the magnetic properties and magnetic-entropy changes of the MnFeP0.5Ge0.5−x Si x compounds with x =0.1, 0.2, 0.3, 0.4 and 0.45. X-ray diffraction shows that the compounds crystallize in the Fe2P-type hexagonal structure. The lattice parameter a and the Curie temperature decreases with increasing x. The maximal magnetic-entropy changes for x =0.4 and 0.45 derived from the magnetization data are about 6.0J/kgK and 5.8J/kgK, respectively, for a field change from 0 to 1.5T. [Copyright &y& Elsevier]

The MnFeP0.56Si0.44 compound is investigated by x-ray diffraction, magnetic measurements, and x-ray absorption fine structure spectroscopy. It crystallizes in Fe2P-type structure with the lattice parameters a = b = 5.9823(0) Å and c = 3.4551(1) Å and undergoes a first-order phase transition at the Curie temperature of 255 K. The Fe K edge and Mn K edge x-ray absorption fine structure spectra show that Mn atoms mainly reside at 3g sites, while 3f sites are occupied by Fe atoms. The distances between the absorbing Fe atom and the first and second nearest neighbor Fe atoms in a 3f-layer shift from 2.65 Å and 4.01 Å in the ferromagnetic state to 2.61 Å and 3.96 Å in the paramagnetic phase. On the other hand, the distance between the 3g-layer and 3f-layer changes a little as 2.66 Å–2.73 Å below the Curie temperature and 2.68 Å–2.75 Å above it. [ABSTRACT FROM AUTHOR]

Abstract: Maghemite (γ-Fe2O3) nanoparticles can be prepared in a single step by the direct thermal decomposition of an Fe–urea complex ([Fe(CON2H4)6](NO3)3). The result of X-ray powder diffraction (XRD) suggests the formation of γ-Fe2O3 whose lattice constant is 8.352Å. The average crystallite size of the nanoparticles is estimated to be 24nm. The formation of γ-Fe2O3 is further confirmed from an infrared spectrum. Magnetic measurements show that the nanoparticles exhibit ferromagnetic characteristics with a relatively large coercivity of 212Oe and remanent magnetization of 16.8emu/g and have the maximum saturation magnetization of 67.4emu/g. [Copyright &y& Elsevier]