Molecular field calculations of the magnetization process in CeBi

Abstract

The complicated magnetization processes of CeBi have been studied in terms of a molecular field model. A long range oscillatory exchange interaction between Ce ions along the [001]-axis is employed in a wave-like-form molecular field. H m( i) = Σ q λ( q, φ q )〈 J q 〉cos(π qi+φ q ), and strong ferromagnetic interactions within the (001)-planes are included. The wavenumber dependent molecular field coefficient, λ( q, φ q ), is a sensitive function of temperature for 12 K < T ≤ 25 K (= T N), and it takes a maximum at q=1 and φ q = 0 and this stabilizes the magnetic structure with a sequence of + -. For T ≤ 12 K, the λ( q, φ q ) is almost independent of temperature. Calculations reproduce the five-step magnetization process for T ≤ 12 K and the four-step process for 15 K < T<22 K. Numerical results on the wave-like molecular fields and sums of simple harmonic functions for the thermal averages of the total angular momenta, 〈 J q 〉cos(π qi+φ q ), are also presented. A brief discussion is made on the simplified Hamiltonian.