VARIATION OF A20 WITH NITROGEN-CONTENT IN SM2FE17N3-DELTA COMPOUNDS

The value of the second-order crystal-field coefficient A20 has been determined as a function of the nitrogen content in Sm2Fel7N3-delta by employing an "change and crystal field model, in which the three lowest J-multiplets were taken into account, assuming that the role of crystal field terms higher than second-order is negligible at room temperature. A linear dependence of A20 on 8 is found with a slope Of dA20/d-delta = +63 K-a0(-2). A20 reaches a value of -245 K-a0(-2) for delta = 0.06, which is slightly larger than that of SmCo5. A bonding charge model (BCM) based on Pauling's chemical bond picture has been proposed here which gives a quantitative account of the effects of nitrogenation on the crystal field. The enhancement Of Samarium anisotropy after nitrogenation can be explained by the Sm-N bonding.