Y. Otani

Gas-phase carbonation of R2Fe17; R = Y, Sm

Abstract Carbides of composition R 2 Fe 17 C x ( x ≈2; R = Y , Sm) are formed by reaction of a powder of the 2:17 parent alloy in a hydrocarbon gas (methane, acetylene, butane) at around 550°C. Unit cell volumes, and Curie temperatures are comparable to those of the corresponding nitrides, and they are substantially larger than the values found in carbides obtained from the melt.

Magnetic properties of a new family of ternary rare‐earth iron nitrides R2Fe17N3−δ (invited)

A series of interstitial ternary nitrides R2Fe17N3−δ has been prepared via a gas‐solid reaction for R=Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu, and Y. These nitrides have structures related to the Th2Zn17 or Th2Ni17 structures of the R2Fe17 parent compounds, but the unit cell volumes are 6%–7% greater, and the Curie temperatures are approximately 400 K higher. The Fe‐Fe exchange interactions are increased by a factor of 2.8 by nitrogenation, whereas the R‐Fe exchange interactions are little changed. All compounds exhibit easy‐plane anisotropy at room temperature, except for Sm2Fe17N3−δ, which shows strong uniaxial anisotropy and may be used to make permanent magnets. The Er and Tm compounds exhibit spin reorientations below room temperature. The anisotropy due to the iron sublattices is easy plane (K1 = −1.3 MJ/m3 at 4.2 K for Y2Fe17N3), but it changes sign to easy axis with cobalt substitution (K1 ≊ 1.0 MJ/m3 at 4.2 K for Y2(Fe1−xCox)17N3−δ when x≥0.2).

Metal bonded Sm2Fe17N3−δ magnets

Sm2Fe17N3−δ is a promising permanent magnet material but disproportionation above 650u2009°C means that only low‐temperature processing can be considered. Sintering micron‐size Sm2Fe17N3−δ powder with the soft, low‐melting metals Zn, Bi, Sn, and Al has been investigated. Good results are obtained with zinc. A coercivity of 0.6 T and a maximum energy product of 84 kJ/m3 (10.5 MGOe) have been obtained. Zn7Fe3 is formed as a secondary phase.

Magnetostatic interactions between magnetic arrays and superconducting thin films

Abstract Two-dimensional arrays of amorphous Gd-Co square particles with thickness around 200 nm were fabricated on 20 nm thick Nb films by means of high-resolution e-beam lithography and sputter deposition. Interesting oscillations due to the fluxoid quantization were observed in the magnetoresistance measured around the superconducting transition temperature of Nb films. The superconducting state of the Nb films seems to be modulated by stray fields produced by the square magnetic particles.

Magnetic and transport properties of ferromagnetic particulate arrays fabricated on superconducting thin films

Abstract Two-dimensional arrays of amorphous R-Co (R = Sm and Gd) square particles were prepared on 200Athick niobium films. Demagnetizing processes studied as a function of spatial periodicity are very different from those of uniform films with no pattern. Calculations show that the inter-particle dipolar interactions are negligibly small compared to self dipolar interactions. Interesting periodic oscillations were observed in the magnetoresistance measured around the superconducting transition temperature of the niobium film ( T c =7.1 K).

Gas-phase carbonation of R2Fe17

Abstract The Curie temperatures of the R 2 Fe 17 series are raised by approximately 330 K after reaction with butane at 780 K to form the interstitial carbides R 2 Fe 17 C 3−δ . Only the Sm carbide shows easy-axis anisotropy at room temperature, with an anisotropy field of 16 T. The Er and Tm carbides exhibit spin reorientations at lower temperature.

High‐resolution observation of magnetization processes in 2 μm × 2 μm × 0.04 μm permalloy particles

The magnetization process in an array of 2 μm × 2 μm × 0.04 μm permalloy particles fabricated on a 100 nm carbon membrane was investigated by means of high‐resolution Lorentz microscopy and electron holography in magnetic fields parallel and perpendicular to the film surface. For perpendicular fields, the magnetization reversal was found to begin with the nucleation of a vortex which gradually transformed into a closure domain configuration. At the remanent state, the flux closure was achieved with the generation of a new type of doubled domain wall.

Giant room temperature volume magnetostriction in an FeRhPd alloy

Abstract Thermal expansion and magnetization in the temperature range 150–800 K and magnetostriction measurements using a high pulsed magnetic field up to 15 T have been performed on the alloy Fe 1.005 Rh 0.85 Pd 0.15 ) 0.995 . We have found a huge volume magnetostriction at room temperature ( ω = 8×10 −3 ), which appears at a determined critical value of the applied magnetic field. These results were explained on the basis of recent band structure calculations.

Magnetization processes in Nd-Fe-B permanent magnets

La boucle dhysteresis de Nd 15 Fe 77 B 8 peut etre decomposee en boucles dhysteresis de deux phases magnetiques; lune avec une coercitivite faible comparativement, lautre avec une coercitivite elevee. Le rapport de volume de ces phases depend de la temperature et de langle entre le champ externe et le pseudo axe c

Demagnetization process and magnetic seeds for R-Fe-B permanent magnets

To investigate the demagnetization process of R-Fe-B permanent magnets (R = rare earths), magnetic hysteresis loops for Nd 15 Fe 77 B 8 and-Pr 15 Fe 77 B 8 magnets were measured at temperatures from 4.2 to 300 K by using a vibrating sample magnetometer and a 100 kOe superconducting magnet. The hysteresis loops were also measured for Nd 15 Fe 77 B 8 magnets coated with Nd by sputtering to examine the nucleation mechanism at surface defects. The demagnetization curve for Nd 15 Fe 77 B 8 magnet exhibits a stepwise decrease in a temperature range from 4.2 to 150 K where a spin reorientation occurs. On the contrary, those of Pr 15 Fe 77 B 8 show a less remarkable stepwise decrease, because the Pr magnet exhibits no spin reorientation. This stepwise decrease is quantitatively explained in terms of a spin reorientation, together with the misorientation of the c-axis in each grain about the aligned axis. The magnetization reversal for the Nd-Fe-B magnet without Nd-coating occurs with many large Barkhausen jumps. The Nd-coating is effective in increasing the coercive force significantly. This effect is discussed in terms of magnetic seeds for the nucleation of magnetization reversal.