Hideya Onodera

Neutron Powder Diffraction on Ce 11B 2C 2 and Nd 11B 2C 2: A New Model for the Tetragonal Crystal Structure

Crystal structures of CeB 2 C 2 and NdB 2 C 2 were investigated by means of neutron powder diffraction using 11 B enriched samples. Diffraction patterns of Ce 11 B 2 C 2 and Nd 11 B 2 C 2 are very similar to each other, and Rietveld analyses reveal that the crystal structure belongs to a symmetry group of tetragonal P 4/ m b m , where the rare earth atoms occupy 2( a ) sites and the B and C atoms occupy two 4( h ) sites with different positional parameters. The newly determined structure differs from previously reported ones with P 4/ m b m and \(P{\overline 4}2c\) mainly in the site positions occupied by the B and C atoms. The B and C atoms form network planes consisting of non-regular squares and octagons.

Magnetization and coercivity of Mn3−δGa alloys with a D022‐type structure

The D022‐type (Al3Ti‐type) phase in the Mn–Ga system is ferrimagnetic; the spin direction is parallel to the tetragonal c axis. The Curie temperature is about 765 K (for δ=0.67), near the decomposition temperature. We have prepared the D022‐type alloys by annealing the quenched ingots of the high‐temperature phase (γMn phase) at 400 or 300 °C for a long time. The preparation becomes much easier if the ingots are powdered by filing before the annealing. The single‐phase specimens of Mn3−δGa were obtained in the composition range 0.15≤δ≤1.06. The coercivity of some specimens was so large that we measured the magnetization curve in high magnetic fields up to 150 kOe. The room‐temperature values of saturation magnetization, remanent magnetization, and coercivity of the powder sample of the alloy with δ=0.67 are 50 emu/g, 25 emu/g, and 13.5 kOe, respectively. We have also studied the effect of magnetic annealing during the transition from the γMn phase to the D022‐type phase and the effect of the addition of F...

Magnetic properties of a new permanent magnet based on a Nd-Fe-B compound (neomax): I. Mössbauer study

Abstract A new permanent magnet Nd 15 Fe 77 B 8 (NEOMAX) and a related compound Nd 2 Fe 14 B are studied by 57 Fe Mossbauer spectroscopy. The crystal structure of the space group P4 2 /mnm (D 14 4h ) proposed by X-ray and neutron diffraction studies is confirmed through the analyses of Mossbauer spectra which consist of six subspectra corresponding to six nonequivalent Fe sites. One of the Fe sites, the j 2 -site, which is sandwiched between two Fe-hexagons, shows a large magnetic hyperfine field of 346.6 kOe and a large quadrupole splitting of 0.60 mm/s at room temperature. The Fe atoms adjacent to the Nd and/or B atoms show smaller hyperfine fields. It is found out that the spin direction of Fe atoms which coincides with the c -axis at room temperature inclines at an angle of ca. 20° from the c -axis at 77 K.

Mössbauer study of the intermetallic compound Nd2Fe14B. II. Temperature dependence and spin reorientation

Abstract The 57 Fe Mossbauer effects of Nd 2 Fe 14 B were measured in a temperature range of 4.2−300 K. Below the spin reorientation transition temperature T sc = 148 K, the spectra were satisfactorily analyzed with twelve Zeeman sextuplets due to splitting of six crystallographic Fe-sites into twelve non-equivalent sites. It was shown that the magnetic moments of the Fe and the Nd atoms are non-collinearly coupled in the magnetic structure with canted moments below T sc . The directions of the moments at 4.2 K are inclined at 27° for Fe and at 58° for Nd from the c -axis to the [110] direction. The average moments are 2.27μ B for Fe and 3.3μ B for Nd at 4.2 K. The increase of the average hyperfine field with decreasing temperature is suppressed below T sc , and its value at 4.2 K is reduced by 1% from the value of 337 kOe which is observed in Y 2 Fe 14 B and also estimated for Nd 2 Fe 14 B by extrapolating the values above T sc . On the other hand, the Nd moment increases abruptly around T sc as the temperature decreases. The directions of the principal axes of electric field gradients on the six distinct Fe-sites were also obtained. The anomalous temperature dependence of quadrupole splittings and isomer shifts was observed around T sc . They were discussed in a framework of the changes in the band structure and the lattice parameters incidental to the spin reorientation transition.

Characteristic magnetic structure due to antiferroquadrupolar ordering in Ho11B2C2

We determined the magnetic structures of the antiferroquadrupolar (AFQ) ordering material with a tetragonal crystal structure, Ho 11 B 2 C 2 , by neutron diffraction technique. The ground state of ...

Magnetic Properties of Iron in Nanocapsules

We have studied the magnetic properties of fine particles of iron and iron carbide nested in carbon cages (nanocapsules), which were synthesized by arc discharge of carbon rods. It is clarified by Mossbauer spectroscopy and thermomagnetic ( M-T ) curve that these particles consist of α-Fe, γ-Fe and Fe3C. Their coercive force is larger than that of bulk α-iron, being ascribed to the small particle size observed by high-resolution (HR) transmission electron microscopy (TEM).

Mössbauer study of the intermetallic compound Nd2Fe14B. I. interpretation of complex spectrum

Abstract The 57 Fe Mossbauer spectrum of the Nd 2 Fe 14 B compound at room temperature has been analyzed with a set of six subspectra due to six crystallographically non-equivalent sites of Fe-atoms. It was shown that there are three possible sets of six subspectra, and the most suitable one could be selected by considering how the hyperfine field and the isomer shift are influenced by near neighbor atoms. The result is applicable to the analyses of the spectra of Nd 2 Fe 14 B and Ho 2 Fe 14 B at room temperature. The order in magnitude of the hyperfine fields and that of the isomer shifts at the six Fe-sites is much the same for the three compounds, while the quadrupole splittings depend complicatedly on the kind of rare earth atom and/or on the lattice parameters.

The effect of pressure on the electronic states of FeS and studied by Mössbauer spectroscopy

We have measured under pressure Mossbauer spectra of FeS and 3c-type up to 16 GPa and x-ray diffraction patterns of up to 11 GPa at room temperature. It is found for that the compressibilities of the lattice parameters exhibit definite anomalies at around 4.5 GPa and that there is no change in the crystal structure up to 11 GPa. Magnetically ordered Mossbauer spectra are observed below 6.5 GPa for FeS and 4.5 GPa for , whereas the spectra above these pressures are typical of a paramagnetic ordering with a quadrupole splitting. A large reduction in the centre shift is observed at these pressures. It is found that there is a distinct steplike feature of the magnetic hyperfine field at 3.5 GPa for FeS. The electronic states of FeS and are deduced from the volume dependences of the centre shift and the magnetic hyperfine field. Below 3.5 GPa for FeS, the electronic state has an insulating character and the electrons on the iron are well localized and thus contribute to the magnetic moment. In the intermediate-pressure range, from 3.5 to 6.5 GPa for FeS and below 4.5 GPa for , the electronic state is like a semimetallic one. Above 6.5 GPa for FeS and 4.5 GPa for , the electronic bandwidth is large enough to cause the state to become metallic and produces a collapse of the iron magnetic moment.

A Possible Novel Magnetic Ordering in SmRu4P12

We have carried out X-ray absorption spectroscopy, 149 Sm nuclear resonant forward scattering, and 99 Ru Mossbauer spectroscopy of SmRu 4 P 12 . The X-ray absorption spectra indicate that the Sm ions are trivalent up to 14 K. The quantum beats due to magnetic dipolar ordering are observed at 4.5 K in 149 Sm nuclear resonant forward scattering. The temperature dependence of time-integrated intensity in 149 Sm nuclear forward scattering suggests that the magnetic dipolar ordering occurs just below the metal–insulator transition temperature. No significant changes in the parameters are observed between 77 and 5 K in 99 Ru Mossbauer spectroscopy. The present result suggests a magnetic ordering accompanied by a magnetic dipole moment at the metal–insulator transition temperature in SmRu 4 P 12 in spite of the proposal of the magnetic ordering accompanied by a T β -type octupole.

Spin distribution in plastically deformed Fe - Al intermetallic compounds II

The influence of plastic deformation on the magnetic properties has been studied in Fe - Al intermetallic compounds with composition between 30 and 40 at.% Al. The spontaneous magnetization, , increases considerably as a result of plastic deformation between 30 and 34 at.% Al concentration. The Fe - Al compounds containing between 35.0 and 50.0 at.% Al are paramagnetic before plastic deformation and as a result of plastic deformation the magnetic susceptibility increases remarkably. At the same time appears. The ferromagnetic clusters are induced by plastic deformation along the antiphase boundary (APB) ribbons between superpartial dislocations. The cluster along the APB ribbon shows a strong anisotropy whose easy direction of magnetization is within the glide plane. The easy direction of magnetization is consistent with that of the roll-induced anisotropy in alloys. The origin of the spin glass in these compounds is explained by the magnetic anisotropy depending on the atomic arrangement. The conditions of the transition to the ferromagnetic state are discussed.