Satoru Simizu

Synthesis and characterization of Fe16N2 in bulk form

Using molecular beam epitaxy and ion implantation, Japanese workers have formed Fe16N2 in thin Fe films. They report a large magnetic induction for this nitride, ≥2.8 T. In the present study, Fe16N2 has been prepared in bulk form by treating Fe powder with NH3/H2 gas mixtures at temperatures in the range 660–670 °C. The γ phase alloy, which forms under these conditions, was quenched to room temperature to form the α’‐Fe‐N phase and then heat treated at 120–150 °C to form the α‘‐Fe‐N phase. The α’ phase has been prepared in 80% purity, the other phase being nonmagnetic γ‐Fe‐N. The α‘ phase has been prepared in 50% purity, the impurity phases being α‐Fe and γ‐Fe‐N. Magnetic measurements give saturation magnetizations at room temperature of 250±10 emu/g (2.6μB/Fe) for the α’ phase, 285±10 emu/g (2.9μB/Fe) for the α‘ phase, and essentially zero for the γ phase. Mossbauer measurements confirm that nitrogen austenite is nonmagnetic. The anisotropy of Fe16N2 is small but detectable.

Magnetic properties of the low-temperature phase of MnBi

MnBi forms peritectically at ∼450 °C. Preparation of MnBi employing conventional techniques such as arc melting and induction melting results in the segregation of manganese. In order to avoid this segregation, we followed the procedure recommended by Guo et al. [X. Guo, A. Zaluska, Z. Altounian, and J. O. Strom-Olsen, J. Mater. Res. 5, 2646 (1990)] and prepared a low-temperature phase of MnBi by melt spinning, followed by heat treatment. Fine powder of MnBi was prepared by ball milling the melt-spun ribbons for various lengths of time. Magnetic properties of these powders were determined. In particular, the temperature dependent coercivity was studied from room temperature to 360 °C for the powders ball milled for 2 and 10 h. The coercivity is found to increase with the increase in temperature reaching a maximum of 25.8 kOe at 280 °C and then decrease as the temperature is increased further. We also found that a peak in coercivity is observed for the samples milled for 10 h. MnBi shows a first-order tran...

Magnetism of α′-FeN alloys and α″-(Fe16N2) Fe nitrides

Abstract The α′-FeN phase was prepared by treating Fe powder with NH 3 H 2 gas mixtures at a temperature of ≈ 665°C followed by a quench to cryogenic temperatures. Conversion of α to α′ to an extent exceeding 85% has been achieved. α″-FeN is produced by treatment of α′ for ≈ 1 to 2 h at 120–150°C. B sat values obtained for α′- and α″-FeN are 23.5 and 26.6 kG, respectively. The latter corresponds to 2.9μ B Fe atom, a 34% enhancement over that of α-Fe.

Magnetic properties of MnBi1−xRx (R=rare earth) systems

MnBi crystallizes in a NiAs-type hexagonal crystal structure, exhibits a high uniaxial anisotropy, and is potentially useful as a permanent magnet material. We have examined the effect of partial substitution of Bi with rare earth elements on the magnetic properties of MnBi. MnBi1−xRx (R=Nd, Dy) were prepared by mechanically alloying powders of the constituent elements at liquid nitrogen temperature followed by heat treatment. X-ray diffraction and magnetic measurements were performed on powder samples to characterize the samples. We found that in MnBi1−xNdx, coercivity (at room temperature) increases from 0.7 kOe to 6.6 kOe for x=0.0 and 0.3, respectively. In MnBi1−xDyx the coercivity increases from 0.7 kOe to 7.9 kOe for x=0.0 and 0.3. The increase in coercivity may be in part due to the increase in the crystal field anisotropy as Nd or Dy is introduced and in part due to the finer particle size. A magnet made from MnBi shows coercivity of ∼17 kOe. A very fine particle size is considered to be the reaso...

Electron paramagnetic resonance of Er3+, Dy3+, and Gd3+ in Y(CF3SO3)3⋅9H2O

The paramagnetic resonance spectra of 1% Er3+ and 1% Dy3+ substituted in hexagonal Y(CF3SO3)3⋅9H2O (YTFMS) single crystals have been measured at 4.2 K and 9.215 GHz. Resonances due to Gd3+ impurities were identified and studied at 77 K. In each case, the results strongly resemble those for the given ion in an Y(C2H5SO4)3⋅9H2O (YES) or La(C2H5SO4)3⋅9H2O (LaES) host suggesting that R3+ site symmetry in YTFMS is also C3h. For Er3+, the spin Hamiltonian parameters are found to be g∥ =1.62, g⊥ =8.67, A=0.006 cm−1, B=0.030 cm−1, and P=0.001 cm−1. For Gd3+ we find g=1.988, b02 =0.010 88 cm−1, b04 =−0.000 418 cm−1, and b06 =0.000 058 cm−1. In the case of Dy3+, resonance is observed for ions whose major g‐tensor axis coincides with the YTFMS c axis and have g∥ =10.90 and g⊥ ≊0. Another resonance, which splits into a six line pattern when the field is rotated away from the c axis, is attributed to ions whose g tensors are tipped by 20° from that axis by the perturbing effect of lattice imperfections. These have gx ...

Magnetism of rare‐earth salts R(CF3SO3)3⋅ 9H2O with R=Tb, Dy, and Ce

Magnetic susceptibilities have been measured between 0.05 and 20 K for three rare‐earth trifluoromethanesulfonate nonahydrates R(CF3SO3)3⋅ 9H2O or RTFMS whose hexagonal crystal structure is very similar to that of the rare‐earth ethylsulfate nonahydrates R(C2H5SO4)3⋅ 9H2O or RES. TbTFMS and DyTFMS order ferromagnetically at TC=0.240 K and TC=0.111 K, respectively. CeTFMS remains paramagnetic down to 0.089 K. All three compounds show extreme Ising‐type anisotropy with g⊥∼0. g∥ of each RTFMS compound compares favorably with that of the corresponding RES as expected from crystalline field theories based on a point‐charge model. In each case, the Weiss constant is close to what is expected for a system with predominantly dipolar interactions. The ferromagnetic ordering in TbTFMS and DyTFMS is essentially that of a dipolar Ising system. The splitting Δ of the ground quasi‐doublet in TbTFMS is only ∼0.5 K and the ordering appears to be largely explained by electronic models although substantial ordering of nucl...

Magnetism of hydrated rare‐earth bromates

The dc magnetic susceptibility has been measured for several rare‐earth bromates, R(BrO3)39H2O, RBR, (R=Pr, Tb, Dy, Er, Tm), using a SQUID magnetometer between ∼0.06 and 4 K. The hexagonal structure of RBR crystals is similar to that of the rare‐earth ethylsulfates, RES. Ferromagnetic transitions were observed at 0.125 K for TbBR and 0.170 K for DyBR. For other RBR no ordering was detected to the lowest temperature attained. The magnetic properties observed for all RBR studied here are very similar to those of corresponding RES but show subtle and interesting differences reflecting small differences in the crystal fields. As in the RES, short‐range exchange interaction in the RBR appears to be negligible compared with dipolar interaction.

Magnetic ordering in Ho(CF3SO3)3⋅9H2O and Ho(C2H5SO4)3⋅9H2O

The magnetic susceptibilities χ∥ and χ⊥, both ac (80 Hz) and static, of hexagonal crystals of the structurally similar Ho(C2H5SO4)3⋅9H2O, HoES, and Ho(CF3SO3)3⋅9H2O, HoTFMS, have been measured down to ∼0.1 K. Both order ferromagnetically along the c axis at Tc=0.23 K. Analysis of the susceptibilities above Tc shows g∥≊15.5 and g⊥≊0, ground doublet‐excited singlet separation 8.4 K in HoES and 15 K in HoTFMS, and dipolar interionic interactions. Cp for both salts was also measured and found to exhibit similar sharp cooperative λ peaks at 0.23 K due to ordering of the Ho3+ moments. This peak sits atop the rounded Schottky anomaly of a system of nuclear spins in a fixed hyperfine field. The independence of the electron and nuclear contributions to Cp is associated with the Ising character of the Ho3+ ground non‐Kramers doublet.

Magnetic characteristics of RCo13−xSix alloys (R=La, Pr, Nd, Gd, and Dy)

The magnetism of LaCo13‐type alloys such as LaCo13, PrCo13−xSix, etc., has recently received considerable attention as potentially useful magnetic materials. The present study is concerned with RCo13−xSix where R=La, Pr, Nd, Gd or Dy.

Exchange coupling in FePt permanent magnets

FePt (for 40–60 at. % Fe) exhibits an order–disorder transformation. The disordered phase is face centered cubic and magnetically soft while the ordered phase is tetragonal and shows high magnetic anisotropy. Since the changes in volume between the two phases are small, it is easy for the soft and hard phases to coexist in a uniform manner. Thus, we have an ideal system with which to investigate the basic features of exchange coupled magnets. Bulk Fe0.6Pt0.4 exhibits reasonably large permanent magnetic properties with a maximum energy product of ∼15 MG Oe (120 kJ/m3) without the need for special processes to promote grain alignment. The high energy product is partially a result of the high ratio of remanence to the saturation induction which amounts to 0.68 as opposed to the ratio of 0.5 for an assembly of randomly oriented uniaxial magnets. This enhanced remanence is predicted by the exchange-spring magnet model for a mixture of cubic and uniaxial phases. In order to verify that the high remanence of the...