Landau theory for magnetic and structural transitions in CeCo_0.85Fe_0.15Si

Abstract

We present a phenomenological analysis of the magnetoelastic properties of CeCoFeSi at temperatures close to the Néel transition temperature T . Using a Landau functional we provide a qualitative description of the thermal expansion, magnetostriction, magnetization and specific heat data. We show that the available experimental results (Correa et al 2016 J. Phys.: Condens. Matter 28 346003) are consistent with the presence of a structural transition at [Formula: see text] and a strong magnetoelastic coupling. The magnetoelastic coupling presents a Janus-faced effect: while the structural transition is shifted to higher temperatures as the magnetic field is increased, the resulting striction at low temperatures decreases. The strong magnetoelastic coupling and the proximity of the structural transition to the onset temperature for magnetic fluctuations, suggest that the transition could be an analogue of the tetragonal to orthorhombic observed in Fe-based pcnictides.

Strong magnetoelastic effect in CeCo1−xFexSi as Néel order is suppressed

“…2 shows the corresponding linear thermal-expansion coefficient α L (=α V /3, the volume thermal-expansion coefficient, given the non-textured nature of the polycrystalline samples) for the selected concentrations. As we pointed out previously [12], the tail in the specific heat at x =0.15 exhibits a remarkably large coupling to the lattice as shown by the double peak structure in α L , which is consistent with the presence of a structural transition preceding the magnetic transition according to a mean field model [13]. This large spin-lattice coupling is now further confirmed by the thermal-expansion at x =0.23.…”