ANALYSIS OF MAGNETIC ANOMALY IN BCC IRON

The depression of the homodiffusion coefficient of iron upon magnetic ordering is analyzed with the use of the Heisenberg model and Kirkwood's method. Data of Lai D. Y. F. and Borg R. J. (Trans. AIME 233 (1865), 1975) and Hettich G., Mehrer H. and Maier K. (Scripta Met. 11 (1977), 795) extended to the temperature range 511÷1200 ‡C have been used in this analysis. The computer fit of an analytic form, derived for the excess activation enthalpy δHp, to the experimental data enabled us to calculate the values of exchange integral J0=(345·3±3·6)k and of the paramagnetic temperature Tp=(1207±15) K. The activation enthalpy of homo-diffusion in a completely ordered ferromagnetic α-Fe is higher by the value δHp=(56·41±±0·59) kJ/mol than the value corresponding to a paramagnetic state. The expression for δHp, the experimental values of J0 and Tp and the Zener's theory of the frequency factor D0 have been used to develop an equation giving the temperature variation of the homodiffusion coefficient in BCC iron for both, above and below the Curie temperature. A treatment analogous to the Bragg-Williams description of order-disorder in alloys was used to demonstrate that the long-range order parameter in ferromagnets is identical to the spontaneous magnetization ℒ. The quotient of δHp(T)/δHp(0) may be well used as a short-range order characteristic. © 1979 Academia, Publishing House of the Czechoslovak Academy of Sciences.