Structure and magnetic properties of R2Fe14B1-xCx compounds (R=Y,Nd)

Abstract

Magnetization curves parallel and perpendicular to aligned direction were measured in an extraction magnetometer (magnetic field up to 80 kOe) on R2Fe14 B0.5 C0.5 compounds (R = Y,Nd) from 1.5 to 300 K. Modified Sucksmith-Thompson method was used to determine anisotropy constants K1 and K2. It was found that the mean Fe moment, Curie temperature and spin reorientation temperature of the Nd-containing compound were decreased upon substitution of carbon for boron, however, the anisotropy field Ha was increased with such substitution. X-ray diffraction analysis showed that values of (1 - α(c/a)2) of the compound in which boron was partially substituted by carbon was larger than that of the unsubstituted one. It is thought that the crystal field acting on the Fe sublattice is increased with carbon substitution. The decrease of Tsr of Nd2Fe14B0.5C0.5 compared with that of Nd2Fe14B is probably due to the increase of the Fe sublattice anisotropy. The value of Ha determined by the SPD method differs significantly from that derived by 2(K1 + 2K2)/Ms. It seems that the anisotropy constants K1, K2 determined by the Sucksmith-Thompson method does not completely represent the anisotropy behaviour of this type of compound. The nominal R2Fe14C samples are a mixture of two phases (R2Fe17Cx + α − Fe) and the Nd2Fe14B type compound was not found in this case. The fact that R2Fe17Cx has a higher Curie temperature compared to that of R2Fe17 is worth noticing.