Magnetic properties of TbCu 7 ‐type Sm‐Fe‐Co‐W‐Cr system nitriding compounds

Experiments were carried out to investigate the magnetic properties of Sm‐Fe‐Co‐W‐Cr system nitriding compounds with TbCu 7 ‐type structure. Sm 10 (Fe 0.95 −Co 0.05 ) 89.7− x W 0.3 Cr x ( x = 0 − 0.7) alloy ribbons were prepared by the single roller rapid‐quenching method, and the effects of alloy composition, and conditions of heat‐treatment and nitrogenation, were examined with regards to their magnetic properties. The optimum preparation conditions of the compounds are as follows. Composition: {Sm 10 (Fe 0.95 Co 0.05 ) 89.4 W 0.3 Cr 0.3 } 85.0 N 15.0 , roller velocity: 50 m/s, heat treatment: 675 °C × 60 min in high‐purity Ar gas, and nitriding conditions: 420 °C × 10 h in high‐purity N 2 gas. Typical magnetic properties of the obtained compound powders are σ τ = 123.7 × 10 −6 Wb · m/kg, H cJ = 706.0 kA/m, (BH) max = 139.4 kJ/m 3 (17.4 MGOe), and T c = 508 °C. It was found that this sample was an exchange spring magnet from TEM photographs and recoil loops of the hysteresis curve. The value of (BH) max for the compression molding isotropic bonded magnet prepared from the {Sm 10 (Fe 0.95 Co 0.05 ) 89.4 W 0.3 Cr 0.3 } 85.0 N 15.0 powder is 102.9 kJ/m 3 (12.9 MGOe), when the density of bonded magnet is 6.1 Mg/m 3 . The reversible temperature coefficient of J τ is α(J τ = −0.07%/°C, and the temperature coefficient of H cJ in the range of 25 °C to 125 °C obtained by a linear extrapolation is α(H cJ ) = −0.44%/°C. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(2): 1–7, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10339