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Abstract A new quinone compound, p-hydroxymethoxybenzobijuglone (HMBBJ), isolated from Juglans mandshurica by bioassay-guided fractionation, showed cytotoxic activity against HeLa cell line. Its chemical structure was determined by NMR and HREIMS [...]

The effect of substituting Mn for Fe on the structure and magnetic properties of Pr2Fe(sub 17-x)Mnx compounds, with x equal to or greater than zero but less than or equal to nine, has been studied. Results indicate the substitution does not change the structure of Pr2Fe17. The unit-cell volume remains unchanged even if manganese content increases up to x = 2 but increases linearly by 2.5 cubic angstroms per Mn atom up to x =8. Cell volume increases significantly at x = 9. It was also observed that the saturation magnetic moment at 5k decreases with increasing Mn concentration.

X-ray diffraction and magnetization measurements were used to examine the structure and the magnetic anisotropy of R2Co15Al2 compounds. Findings showed that the compounds are in the single phase, having the hexagonal Th2Ni17-type structure for R=Y, Ho, Er and Tm and the rhombohedral Th2Zn17-type structure for R=Ce, Pr, Nd, Gd, Tb and Dy. The Ce compound was found to exhibit an anomalous lattice parameter and magnetic characteristic which are relative to the mixed-valence behavior of the Ce ion.

A study was conducted to analyze the structure and magnetic characteristics of (Nd(sub 1-x)Ce(sub x))(sub 6)Fe(sub 13)Al compounds. The compounds were prepared from 99.9% pure elements by arc melting carried out under at atmosphere of high-purity argon. The samples were then quenched in water after heat treatment. Experimental results indicated a complex temperature dependence of magnetization.

A study was conducted to analyze the structure and magnetocrystalline anisotropy of Ce2Co(sub 17-x)Al(sub x), where x = 0, 1, 2, and 3, compounds. X-ray diffraction and magnetization measurements were carried out. Experimental results indicated that the unit-cell volume, saturation magnetization and Curie temperature of the compounds were anomalously low in comparison with values determined from an extrapolation by the R2Co(sub 17-x)Al(sub x) compounds.

The effect of Mn substitution on the magnetocrystalline anisotropy of [R.sub.2][Co.sub.17-x][Mn.sub.x] (R = Pr, Nd, Tb, Ho and Dy) compounds have been investigated by means of x-ray diffraction (XRD) and magnetic measurements. XRD measurement on magnetically aligned samples demonstrates that for Pr (1 [is less than] x [is less than] 5) and Ho (2 [is less than] x [is less than] 4) compounds, they exhibit an easy-axis type of anisotropy at room temperature, while for Ho (x = 1) compound, an easy-cone type of anisotropy, and for Nd (0 [is less than] x [is less than] 5) and Tb (0 [is less than] x [is less than] 4) compounds, an easy-plane anisotropy. The spin reorientation transitions are found in the M-T curves for Pr (1 [is less than] x [is less than] 5), Nd (1 [is less than] x [is less than] 5), Tb (2 [is less than] x [is less than] 4) and Ho (0 [is less than] x [is less than] 4) compounds. The spin-reorientation temperatures [T.sub.sr] firstly decrease with Mn substitution, and then increase after x [is greater than] 3. The magnetic phase diagrams are given. The spin-reorientation transition might be understood as the result of the competition between the magneto-crystalline anisotropy of the R-sublattice and that of the 3d-sublattice. Room-temperature magnetocrystalline anisotropy fields [H.sub.A] firstly increases and then decreases with increasing Mn substitution, attaining the maximum at x = 2-3. The enhancement of anisotropy is explained by preferred substitution of Mn atom in 6c Co sites. From the measurement of magnetization curve along and perpendicular to the c-axis at different temperature around the [T.sub.sr], it can be implied that the spin-reorientation transitions are a continuous moment reorientation. Index Terms--Magnetic materials, magnetocrystalline anisotropy, rare-earth transitional metal compounds, spin reorientation.