Crystal and magnetic structure of the permanent magnet material Tb 2Fe 14C

Abstract

R 2Fe 14C (R = rare earth metal) compounds are considered as new permanent magnet materials of technical interest. Investigations of the compound Tb 2Fe 14C by means of X-ray and neutron diffraction as well as by metallographic techniques were carried out. Tb 2Fe 14C crystallizes in the tetragonal space group P4 2 mnm and is isotypic to Nd 2Fe 14B. Lattice constants are a = 8.7772(2) A ̊ and c = 11.8708(5) A ̊ at 295 K. The nuclear and magnetic structure of Tb 2Fe 14C has been investigated by means of neutron diffraction at 723 K (above the Curie temperature T c ), at 585 K (just below T c ), at room temperature and at 23 K. The magnetic moments of the terbium atoms are oriented antiparallel to the magnetic moments of the iron atoms and parallel to the c axis. They do not exhibit any reorientation tendency with increasing temperature. The measurement of the magnetization curve by means of neutron diffraction yields a T c of 620 K which is significantly higher than T c = 572–600 K determined by bulk magnetization measurements. The nuclear structure of Tb 2Fe 17 (Th 2Zn 17 structure type) has been refined simultaneously as such an impurity phase was present in the sample.