Takahiko Iriyama

High‐resolution neutron powder diffraction study on nitrogenated Nd2Fe17

High‐resolution neutron powder diffraction measurements with λ=1.8232 A and collimation of 6’‐20’‐6’ on Nd2Fe17Nx with x=0, 2.85, and 2.91 were carried out at room temperature. Structural parameters and magnetic moments were determined by the Rietveld profile‐fitting calculation. The magnetic moments of iron atoms increased with increasing nitrogen concentration; e.g., the magnetic moments of iron located at 6c, 9d, 18f, and 18h sites increase from less than 0.7μB in the x=0 sample to about 2.1μB in the x=2.91 sample. It is noticed that a local atomic group composed of two Fe(1) atoms at the 6c site plus six Fe(3) atoms at the 18f site keeps its shape against the nitrogen uptake.

High‐field magnetization process in Sm2Fe17N3.0: Importance of exchange‐enhanced mixing of excited J multiplets

The high field magnetization process in Sm2Fe17N3.0 has been investigated by using dc magnetic fields of up to 260 kOe generated by a hybrid magnet. It was found that the hard‐axis magnetization at 4.2 K is only 78% of the easy‐axis value in the field of 260 kOe, while at 296 K, it almost saturates at the same field, the saturation value being about 3% smaller than that along the easy axis. Experimental results have been analyzed on the basis of a model calculation taking the excited J multiplets of the Sm ion into account. It has been found that, when the field is applied along the hard axis at 296 K, the Sm magnetic moment rotates away from the field direction and finally, at the saturation field, it becomes antiparallel to the field so that the Sm and Fe moments are arranged ferrimagnetically. The origin of such a magnetization process was clearly explained as a result of the mixing of the excited J multiplets caused by the Sm–Fe exchange interaction. Observed anisotropy of saturation magnetization at ...

Mössbauer spectrometric study of Sm2Fe17Nx(x=0-8)

Ternary rare-earth-iron-nitrogen compounds of Sm2Fe17Nx with x ranging from 0 up to 8, which have a rhombohedral structure of Th2Zn17 and a high Curie temperature up to 475–480°C depending on the degree of nitrogenation, were prepared by the nitrogenation of arc-melted Sm2Fe17 in mixed ammonia and hydrogen gas atmospheres of various ratios, and Mössbauer spectra of these compounds were observed at room temperature in order to analyse the physicochemical state of the nitrogenated products. The obtained data were analysed by focusing main attention on the effect of degree of nitrogenation on the variation of spectral profiles. Paramagnetic peaks due to an amorphous compound became prevalent as x became higher than ~ 2.3.

X-ray diffraction study of Sm2(Fe1−xAlx)17 single crystals with x=0.058, 0.081

Abstract Crystal structures of rare-earth iron compounds, Sm 2 (Fe 1− x Al x ) 17 with x =0.058 and 0.081, were successfully determined assuming the space group R3m (No.166) by means of single crystal X-ray diffraction at room temperature. In these compounds, aluminum atoms partly substitute for iron atoms, Fe(4), at the 18h ( x ,− x , z ) site. In Sm 2 (Fe 0.919 Al 0.081 ) 17 , a small amount of aluminum substitution is noticed for iron atoms at the 18f ( x ,0,0) site. Unit cell volume expansion due to the substitution causes appreciable increase in Sm–Fe(4), Fe(3)–Fe(4) and Fe(4)–Fe(4) interatomic distances. A local atomic group consisting of only Fe atoms at the 6c site (dumbbell) and the 18f site (ring) keeps its shape against the aluminum substitution.

Neutron diffraction study on Y2Fe17 and Y2Fe17Nx (x = 2.1–2.6)

Abstract R 2 Fe 17 compounds, where R refers to yttrium or one of the rare-earth metals, have the hexagonal Th 2 Ni 17 -type or the rhombohedral Th 2 Zn 17 -type structure. Since yttrium, Y, has a relatively small ionic radius similar to that of Dy, the hexagonal structure is stabilized. A main purpose of this study is to determine the magnetic and chemical crystal structures of Y 2 Fe 17 and nitrogenated Y 2 Fe 17 at temperatures from 10K to ambient, by means of high-resolution powder neutron-diffraction measurements using JRR3M-HRPD. The powder samples used for the present study turned out to be mixtures of the hexagonal (50–60 vol%) and the rhombohedral (the rest) phases.

First-order magnetization process in Nd2(Fe1−xAlx)17 single crystals

Abstract High field magnetization measurements have been performed for single crystals of Nd 2 (Fe 1− x Al x ) 17 . In the sample with x = 0.04, the easy direction is not within the c -plane at 4.2 K but in the plane spanned by the b - and c -axes. When the field is applied along the c -axis at 4.2 K, abrupt increases in magnetization have been observed successively at 115 and 150 kOe. These results have been well reproduced by a simple model calculation on the basis of the crystalline electric field theory.

Thermal behavior of ternary Sm2Fe17Nx magnets

The Mössbauer spectra of Sm2Fe17Nx, prepared by the nitrogenation of Sm2Fe17 powders in an ammonia and hydrogen atmosphere, were observed at elevated temperatures to shed light on the thermal behavior of nitrogen in the compounds Sm2Fe17Nx. It was found that there were large differences in thermal behavior between the starting Sm2Fe17, crystalline Sm2Fe17Nx (x≈1.7) and amorphous Sm2Fe17Nx(x∼7).The thermal decomposition behavior of Sm2Fe17N3.2, developed as one of the most promising hard magnetic materials, was found to be different under different atmospheres.ZusammenfassungZur Klärung des thermischen Verhaltens von Stickstoff in Sm2Fe17Nx-Verbindungen wurde bei höheren Temperaturen das Mössbauer-Spektrum von Sm2Fe17Nx auf-genommen, wobei die Verbindung aus Sm2Fe17 durch Nitrierung in Wasserstoffatmosphäre hergestellt wurde. Man fand, daß erhebliche Differenzen zwischen dem thermischen Verhalten des Ausgangsstoffes Sm2Fe17, kristallinem Sm2Fe17Nx (x∼1.7) und amorphem Sm2Fe17Nx (x∼7) bestehen.Für unterschiedliche Atmosphären fand man unterschiedliches thermisches Zersetzungsverhalten von Sm2Fe17N3.2, entwickelt als eines der vielversprechendsten harten magnetischen Materialien.

High-Field Magnetization Study of Sm2Fe17Nx and Related Compounds

Magnetic and crystallographic properties of Sm2Fe17Nx with x>3.0, nitrogenated by using a mixed gas of NH3 and H2, have been investigated by comparing the results of two groups of samples: as-nitrogenated samples which contain hydrogen (0.2 to 0.4/f.u.) and annealed samples which are hydrogen-free. The lattice constant c of the Th2Zn17 structure of the hydrogen-free sample is found to be slightly smaller than that of hydrogen-contained sample, the former value, however , being still larger than that of Sm2Fe17N3.0. The saturation magnetization increased slightly by the dehydrogenation treatment, although it is still considerably smaller than that of Sm2Fe17N3.0.