On the coexistence of low- and high-spin states in transition metal systems

Abstract

We discuss the unusual magnetic behaviour of itinerant magnetic systems close to magnetovolume instabilities. It is shown that the unusual properties result from transitions between, and coexistence of, high-spin (HS) and low spin (LS) states. We argue that the Invar effect is related to the coexistence of LS and HS states over a substantial temperature range. For the theoretical description an expansion of the free energy in terms of the magnetization and volume is used, which at zero temperature reproduces one-electron band structure results obtained with the fixed-spin-moment (FSM) method (1).