Naoki Ohkubo

Mössbauer Spectroscopy of Langbeinite-Type K2Fe2(SO4)3

The langbeinite-type K 2 Fe 2 (SO 4 ) 3 was synthesized. The temperature dependence of the dielectric constant shows a clear anomaly at about 130 K. Mossbauer spectrum of 57 Fe was recorded in the temperature range from 15 to 290 K. The spectrum at all temperatures consists of two doublets which are analyzed with isomer shifts and quadrupole couplings. The quadrupole splitting of one site is 3.00 mm/s at 290 K and shows only 10% increase down to 15 K. The other one is 0.82 mm/s at 290 K and shows a drastic increase, resulting at 15 K in 2.5 times that at 290 K. The two 57 Fe sites for the electric field gradient were assigned to the two crystallographically inequivalent iron sites compairing the two octahedral oxygen environments of the iron ions. The broad background spectrum is interpreted as the distribution of the electric field gradient due to the multi-positional distribution in SO 4 groups proposed by Itoh et al.

Magnetic and crystallographic properties of deuterides YFe2Dx

The isothermal deuterium absorption and desorption experiments, X-ray and magnetization measurements revealed four types of deuterides in YFe 2 D x , γ 1 of 3.8< x , γ 2 of x <3.4, and β and amorphous of x <2.1 at room temperature. The crystal structure of all deuterides are rhombohedral. The magnetization of all deuterides are about 3.8 µ B /YFe 2 D x and the Curie temperatures are 120 K for the γ 1 -deuteride and 300 K for the γ 2 -deuteride. The β-deuteride is always a mixture with the amorphous deuteride, and the Curie temperature of amorphous deuteride is 570 K and that of β-deuteride varies from 290 K to 400 K with increasing deuterium concentration. Mossbauer mesurements were performed and hyperfine fields of Fe were estimated for every deuterides.

Effect of beryllium on magnetism of R2Co17Be

Abstract X-ray and magnetization measurements were performed for R 2 Co 17 and R 2 Co 17 Be in order to investigate the effect of beryllium on the magnetic properties. Addition of beryllium makes Th 2 Zn 17 structure more stable than Th 2 Ni 17 structure and decreases the magnetization and Curie temperature.

Ferromagnetism of Y2(Fe1−yCoy)17−xAlx

Magnetization and x‐ray measurements of alloy systems, Y2(Fe1−yCoy)17−xAlx (y=1/3,2/3), were performed and the magnetic and crystallographic data are shown with the results of the systems where y=0 and 1.0. The crystal structure of all alloys changes from hexagonal Th2Ni17 type to rhombohedral Th2Zn17 type with increasing aluminum concentration. The average magnetic moments of the 3d metal atom of all alloy systems decrease with increasing aluminum concentration. The Curie temperatures of the alloy systems where y=1/3, 2/3, and 1.0 decrease smoothly with increasing aluminum concentration. On the other hand, the system where y=0 at first increases and then decreases. These magnetic properties are discussed by Stoner’s model.

Magnetic properties of R2T17-type Dy2Fe17−xAlx compounds

Magnetization and Mossbauer measurements on R 2 T 17 -type Dy 2 Fe 17-x Al x compounds were performed. The crystal structure is of Th 2 Ni 17 type for x≤5 and Th 2 Zn 17 the for 5<x<8. With increasing Al content, the magnetization decreases and the Curie temperature increases for x≥3 and then decreases for x≥3. Mossbauer spectra of Fe suggest two types of iron, and the hyperfine fields decrease with increasing Al content. The assignment of the magnetic moments of Fe and Dy is discussed

Magnetic and neutron diffraction study on Ni2In type (Mn1−xPdx)2Ga

Pseudobinary intermetallic compounds (Mn1−xPdx)2Ga of Ni2In type structure are found in the range of 0.3≦x<0.6. This article describes the results of investigations of the crystal and magnetic properties of the phase with x-ray and neutron diffraction, as well as magneto metric methods. The neutron diffraction study for x=0.4 proved that in the Ni2In type crystal structure, the 2(a) site is occupied by Mn atoms, the 2(d) site by Pd and residual Mn atoms, and the 2(c) site is occupied by Ga atoms. (Mn1−xPdx)2Ga compounds exhibit a ferromagnetic nature characterized by TC, and in the temperature below TN, antiferromagnetic components originating from canted spin structure in 2(a) structures in the 2(a) site. It is similar to canted spin structures of CoMnSn. The existence of a small concave region in the magnetization–temperature dependence curve is discussed in terms of the canting of spins in the 2(a) site.

Magnetic properties of YBa2Cu3−xRhxOy and YBa2Cu3−xIrxOy (x=1, 2, 3)

Abstract The crystallographic and magnetic properties of YBa2Cu3−xRhxOy and YBa2Cu3−xIrxOy (x=1,2,3) have been studied. The structures are orthorhombic, tetragonal and cubic with a mixture of them. YBa2Ir3Oy is a weak ferromagnet with T C =185 K . YBa2Cu2RhOy and YBa2Cu2IrOy are antiferromagnetic with T N =14 K . The other compounds are paramagnetic.

Mössbauer studies on valence change of rare-earth ions Ce1− xRxFe2 (R = La, Pr, Nd)

Abstract MgCu 2 -type compounds Ce 1− x R x Fe 2 ( R = La, Pr, Nd ) annealed at 1000 K are single phase in x ⩽ 0.2 of R = La , in x ⩽ 0.43 of R = Pr and in x 0.5 of R = Nd . The composition dependence of lattice parameters, magnetization and Curie temperature suggested that some changes occur at x = 0.2, 0.3 in Ce 1− x Pr x Fe 2 and x = 0.15, 0.2, 0.33 in Ce 1− x Nd x Fe 2 . Mossbauer spectra of Fe show that the hyperfine field changes above and below x = 0.2. The increasing rate of magnetization of Ce 1− x Nd x Fe 2 with composition is 3.3 μ B in x 0.3. These facts suggest that Nd in Ce 1− x Nd x Fe 2 is Nd 3+ in x ⩽ 0.2 and Nd 4+ 0.2 . The magnetization and Mossbauer data suggest that Pr in Ce 1− x Pr x Fe 2 is Pr 3+ in x ⩽ 0.2 and La in Ce 1− x La x Fe 2 is La 3+ and Ce 4+ in x ⩽ 0.2. The easy direction of magnetization is [1 0 0] in Ce 1− x R x Fe 2 ( R = La, Pr ) and [1 1 0] in Ce 1− x Nd x Fe 2 .

Magnetic Properties of R2T17 Type Y2Fe17-xAlx Compounds

Magnetization and Mossbauer measurements on R2T17 type compounds Y2Fe17-xAlx were performed. The crystal structure is of Th2Ni17 type for x≤4 and Th2Zn17 type for 5≤x≤7. With increasing Al content, the magnetization decreases and the Curie temperature increases for x≤3 and decreases for x≥3. The composition dependence of the hyperfine field is discussed in conection with the substitution of Al for Fe.

Magnetic Properties of R2T17-Type Compounds Dy2Fe17-x-yAlx with Iron Deficiency

The ternary R<inf>2</inf>T<inf>17</inf>-type alloys Dy<inf>2</inf>Fe<inf>17-x-y</inf>Al<inf>x</inf> with an Fe deficiency have been studied by means of X-ray diffraction and magnetization measurements. The single phase boundary of the R<inf>2</inf>T<inf>17</inf>-type structure was determined to be near the composition Dy<inf>2</inf>Fe<inf>9</inf>Al<inf>x</inf> for x¿4 and near Dy<inf>2</inf>Fe<inf>13-x</inf>Al<inf>x</inf> for x¿4. The crystal structure is of the Th<inf>2</inf>Ni<inf>17</inf> type for alloys with x¿5, and of the Th<inf>2</inf>Zn<inf>17</inf> type for 6¿×¿8. Thermomagnetic curves show that the magnetism changes from P-type to N-type ferrimagnetism with increasing Al content x. Three types of spin arrangements, in which x¿2, 2≪׿5 and 6¿×¿8, were proposed on the basis of the magnetic studies. It was concluded that the substitution of Al for Fe causes a decrease in the Fe magnetic moment, but that an Fe deficiency causes an increase in the Fe magnetic moment.