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NiO/ZnO nanocomposites with NiO content of 4 at. % and 20 at. % were annealed up to 1200 °C to get Ni doped ZnO nanocrystals. Raman scattering spectra illustrate a broad and strong band at 500-600cm-1 in all nanocomposites after annealing above 700 °C, which suggests incorporation of Ni in the ZnO lattice. However, x-ray diffraction measurements show that NiO phase can be still observed in all nanocomposites after annealing, which indicates that Ni is partially doped into the ZnO structure. Positron annihilation measurements reveal large number of vacancy defects in the interface region of all nanocomposites, and they are gradually recovered with increasing annealing temperature up to 1000 °C. Room temperature ferromagnetism can be observed in the NiO/ZnO nanocomposites, which is stronger in the 20 at. % NiO/ZnO nanocomposites, and the magnetization decreases continuously with increasing annealing temperature. This indicates that the ferromagnetism at low annealing temperatures originates from the NiO nanograins, and they become antiferromanetic after subsequent higher temperature annealing which leads to the weakening of ferromagnetism. After annealing up to 1000 °C, the ferromagnetism in both the two samples becomes nearly invisible. The disappearance of ferromagnetism shows good coincidence with the recovery of vacancy defects in NiO/ZnO nanocomposites. It can be inferred that the ferromagnetism is mediated by vacancy defects which are distributed in the interface region. [ABSTRACT FROM AUTHOR]

SmCo7-xCrx (x=0–0.6) magnets have been synthesized by mechanical alloying and subsequent annealing. A small amount of Cr favors the formation of Th2Ni17-type 2:17 phase and increasing the Cr content can extend the temperature range in which the hexagonal 2:17 phase remains stable. The coercivities of the SmCo7-xCrx magnets are significantly enhanced by increasing the Cr content. The highest coercivity of 15.8 kOe is obtained for the SmCo6.4Cr0.6 alloy annealed at 700 °C for 30 min. The transformation of Th2Ni17-type structure to Th2Zn17-type structure is observed when increasing the annealing temperature. The magnetization reversal process of the alloys has been discussed, according to the measurement of initial magnetization curves and minor hysteresis loops. [ABSTRACT FROM AUTHOR]

Dy1-xPrx(Fe0.35Co0.55B0.1)2 (0<=x<=1) Laves compounds with a cubic MgCu2-type structure were synthesized by arc melting and subsequent annealing. The lattice parameter of the Laves compounds linearly increases, while the Curie temperature TC decreases with increasing Pr content. The saturation magnetization Ms at 5 K or 295 K for the Dy1-xPrx(Fe0.35Co0.55B0.1)2 alloys decreases to reach a minimum, then increases with increasing Pr content. The composition for magnetic moment compensation is about x=0.55 at 295 K and x=0.65 at 5 K, respectively. The magnetostriction λ∥ or λ⊥ at room temperature was investigated either parallel or perpendicular to the applied field using a standard strain gauge technique. [ABSTRACT FROM AUTHOR]

A large reversible negative magnetic-entropy change ΔSM has been observed in TbCoC2, accompanied by a second-order phase transition at 28 K. The maximum value of -ΔSM is 15.3 J kg-1 K-1 at 30 K for a magnetic-field change from 0 to 5 T, with the refrigerant capacity of 354 J kg-1. In particular, also the large -ΔSMmax of 7.8 J kg-1 K-1, is obtained for a small field change from 0 to 2 T. The large reversible ΔSM and the high reversible refrigerant capacity in low magnetic field indicate that TbCoC2 may be a promising candidate for magnetic refrigeration at low temperatures. [ABSTRACT FROM AUTHOR]

The spin orientation and spontaneous magnetostriction of multicomponent TbxDy1-x-yPry(Fe0.9B0.1)1.93 (0.10 ≤ x ≤ 0.25, 0.30 ≤ y ≤ 0.60) Laves phases were studied by step-scanning their (440) X-ray diffraction lines. The easy magnetization direction (EMD) of the, Laves phases changed from the «100» to «111» axis when x was increased from 0.10 to 0.25. With increasing y, the EMD of Tb0.15Dy0.85-yPry(Fe0.9B0.1)1.93 and Tb0.2Dy0.8-yPry(Fe0.9B0.1 )1.93 Laves phases `reoriented from the «100» to «111» axis. The magnetostriction coefficient λ111 of TbxDy1-x-yPry(Fe0.9B0.1)1.93 Layes phases increased with increasing x (or y) when y (or x) was kept constant. [ABSTRACT FROM AUTHOR]

The effects of B and C substitution for Sn on phase components, Curie temperature TC, and magnetocaloric effect of melt-spun Mn3Sn2-xMx (M = B, C; x = 0-0.5) ribbons have been investigated. X-ray diffraction (XRD) results show that the main phase in the as-spun Mn3Sn2-xMx (M = B, C; x = 0-0.5) ribbons is Mn3Sn2 of Ni3Sn2-type (Pnma). Minor Mn2B (when x ≥ 0.1) or Mn5C2 (when x > 0.1) secondary phase is formed, and their amounts increase with increasing B and C concentration, respectively. The Curie temperature TC of these ribbons varies in the temperature range of 240-250 K. The peak values of the maximal magnetic entropy change, -ΔSMmax, are about 13.6-18.3 mJ/cm3 K for B-substituted ribbons and 13.6-17.5 mJ/cm3 K for C-substituted ribbons, respectively, at a maximum applied field of 50 kOe. These values are about one fifth that of Gd (81.4 mJ/cm3 K). However, the relatively broader temperature range of the half maximum of ΔSM peak (∼100 K), low-cost and nontoxic elements still make Mn3Sn2-based ribbons the promising candidates for magnetic refrigeration applications close to room temperature. [ABSTRACT FROM AUTHOR]

The effect of Ge on the magnetic properties and crystal structure of melt spun SmCo7-xGex (x = 0-0.8) ribbons have been investigated. SmCo7-xGex ribbons (x = 0-0.6) spun at a high wheel speed of 40 m/s crystallize in the TbCu7-type structure. The x-ray diffraction results analyzed by the Rietveld refinement method show that Ge prefers to occupy the 2e sites in the TbCu7-type structure. The grain size of the ribbons is only slightly decreased with the proper amount of Ge substitution (x < 0.7). When increasing x from 0-0.6, the coercivity of the SmCo7-xGex ribbons is enhanced from 1.9 kOe for binary SmCo7 to 7.5 kOe for SmCo6.5Ge0.5 which is mainly due to the enhancement of the magnetic anisotropy field by the Ge substitution for Co in 2e sites. Furthermore, a slight addition of carbon in the alloy is effective in refining the grain size and further improving the coercivity of the ribbons. Coercivity as high as 11.4 kOe could be obtained for SmCo6.7Ge0.3C0.1 ribbons. [ABSTRACT FROM AUTHOR]