Influence of symmetry on Sm magnetism studied on SmIr2Si2 polymorphs

• First order polymorphic transition between two phases showing high hysteresis.
• Both polymorphs tends to be antiferromagnetic at low temperatures.
• Different magnetic behavior of polymorphs is caused by symmetry of crystal field.
• Ab initio electronic structure calculations confirm the experimental data.

Polycrystalline samples of SmIr2Si2 formed at room temperature both the low temperature phase (LTP) and the metastable high temperature phase (HTP), respectively, depending on the heat treatment. The samples were studied by X-ray powder diffraction, DTA, specific-heat and magnetization measurements with respect to temperature and magnetic field. The first order LTP ↔ HTP polymorphic phase transition has been determined showing the huge temperature hysteresis of 264 °C caused by the high energy barrier due to the change of stacking of the Sm, Ir and Si basal plane sheets within the transition. Both polymorphs show indications of antiferromagnetic order at low temperatures. The considerably different magnetic phase transitions determined for the LTP and HTP confirm the strong influence of crystal structure symmetry on magnetism in the two polymorphs. The magnetism in SmIr2Si2 exhibits typical features caused by the specific behavior of Sm3+ ion characterized by energy nearness of the ground state and first excited state and crystal field influence. The interpretation of experimental results is corroborated by results of ab initio electronic structure calculations.