Wang Fang-wei

EFFECT OF MANGANESE SUBSTITUTION IN R 2 AlFe 16-x Mn x (R=Y,Ho,Nd AND Pr)COMPOUNDS ON STRUCTURAL AND MAGNETIC PROPERTIES

The structural and magnetic properties of R2AlFe16-xMnx (0 ≤ x ≤ 8 for Y, Ho, 0 ≤ x ≤ 10 for Pr, 0 ≤ x ≤ 16 for Nd) compounds have been investigated by means of x-ray diffraction and magnetization measurements. The R2AlFe16-xMnx compounds have a hexagonal Th2Ni17-type structure for R = Y and Ho, and a rhombohedral Th2Zn17-type structure for Nd and Pr. With increasing x, the unit-cell volumes have a small increase initially, followed by a greater linear increase. The Curie temperature and the saturation magnetization of these compounds show marvelous drop with increasing x. Compensation point was observed in the temperature dependence of the magnetization for Ho2AlFe12Mn4 compound.

Negative Magnetoresistance Effect in La-Pb-Mn-O Bulk Manganese Oxides

The structure, magnetic and magnetotransport properties of La1-xPbxMnO bulk manganese oxides prepared by the standard ceramic techniques were investigated by XRD, VSM, ESM and MR measurements. The sintering condition and the hole doped concentration x have a strong influence on the magnetic properties and magnetoresistance effect. The maximum MR, 20% at room temperature under a field of 2 T, was obtained for x = 0.4 and the sintered temperature Ts = 1260°C. The correlation among the structure, magnetic and MR is discussed.

Magnetic properties of Pr2Co17-xMx (M = Ga, Si) compounds

The influence of Ga or Si substitution for Co on the structural and magnetic properties of Pr2Co17 compounds is investigated. All samples studied here are single phase and have the rhombohedral Th2Zn17-type structure. The unit-cell volume is found to increase linearly by the substitution of Ga for Co, but reduce by the substitution of Si for Co in Pr2Co17 compounds. In Pr2Co17-xMx, the Curie temperature decreases monotonically with increasing x at an approximate rate of 153K per Ga atom and 175K per Si atom. The saturation magnetic moment of Pr2Co17-xMx (M = Ga, Si) decreases with increasing x. The rates of the decrease are larger than that expected as a simple dilution. For Pr2Co17-xSix, the spin-reorientation transition is observed above room temperature. The spin-reorientation temperature Tsr first decreases with increasing Si content and then increases at higher x values (x > 2). The spin-reorientation behavior is interpreted by the competition between the Pr and Co sublattice anisotropies. The easy magnetization direction in Pr2Co17-xGax compounds is perpendicular to the c-axis, and no spin reorientation transition is observed.

Magnetic properties of Dy2Fe17-xCrx and Er2Fe17-xCrx (x = 0-3) compounds

The crystal structure and magnetic properties of R2Fe17-xCrx (R = Dy, Er, 0 ≤ x ≤ 3) compounds have been investigated by means of x-ray diffraction and magnetization measurements. These compounds have hexagonal Th2Ni17-type structure. The unit-cell volumes decrease with the increase of Cr concentration x. The Curie temperature Tc of the Er2Fe17-xCrx compounds increases from 320 K for x = 0 to 403 K for x = 1.0 and then decreases with further increase of x. The Curie temperature Tc of Dy2Fe17-xCrx compounds increases from 364 K for x = 0 to 435 K for x = 1.0 and then decreases with further increase of x. The saturation magnetization of these compounds shows an approximately linear decrease with the increase of x. Spin reorientation transitions occurs in Er2Fe17-xCrx (x = 2.0 and 3.0).

Formation and magnetic properties of Dy2Fe17-x Mnx C(x = 0-17) prepared by arc-melting

We report on alloys formed by replacing iron with manganese in the compound Dy2Fe17C1.0. Samples were characterized by x-ray diffraction and magnetic measurements. The 2:17-type structure can be crystallized in the whole range of manganese substitution. The Curie temperature of the series of Dy2Fe17-xMnxC1.0(x = 0-17) drops down considerably from 515 K for x = 0 to about 20 K for compounds with high manganese concentration, and the compensation point was observed in a narrow range of x ≈ 4-6. The rapid decrease of the magnetization shows that the manganese substitution is not a simple magnetic dilution to the transition-metal sublattice moment, it indicates that the moment of Mn may be antiparallel to that of Fe. The field dependence of the magnetization of Dy2Fe17-xMnxC1.0 may indicate the existence of the nonlinear magnetic structure for the samples with high Mn concentrations.