PREPARATION OF SM2FE17NX POWDERS BY MECHA NICAL GRINDING IN NH3 ATMOSPHERE AND THEIR MAGNETIC-PROPERTIES

Sm2Fe17NX magnetic powders have been prepared by mechanical grinding ( MG) in NH3 atmosphere and subsequent nitriding. The influence of the c ompositional difference of starting material and MG conditions on thei r magnetic properties have been investigated. The increase of MG time promotes absorption of nitrogen into powders during nitriding because of the activation of powders. However, too long MG treatment causes th e decrease of nitrogen concentration and deterioration of their magnet ic properties due to the diminution of Sm2Fe17 structure. Therefore, t here is an optimum value of MG time. The grain size of about 100 nm be ing much smaller than the single magnetic domain size of about 270 nm is obtained by MG with a vibration mill. The best value of maximum ene rgy product (BH) max of 50.7 kJ . m(-3) (6.34 MGOe) is obtained by MG with the vibration mill and subsequent nitriding. These powders have b een also prepared by MG with a rotary ball mill whose mechanical energ y is lower than that of a vibration mill. Though the powders obtained by MG in NH3 for 288 ks with a rotary ball mill have the sufficient ni trogen content of about 35000 ppm without subsequent nitriding, their magnetic properties are extremely deteriorated. The powders prepared b y MG for 36 ks with a rotary ball mill and subsequent nitriding in N-2 at 723 K for 21.6 ks show good rectangularity in the demagnetization curve and higher magnetization. The maximum energy product (BH)max and remanence are 129 kJ . m(-3) (16.1MGOe) and 1.0 Wb . m(-2), respectiv ely.