Evidence for magnetic dimers and skyrmion lattice formation in Eu2Pd2Sn

Abstract

The magnetic, thermal, and transport properties of the noncentrosymmetric compound Eu2Pd2Sn are reexamined with the inclusion of detailed measurements. In its paramagnetic phase, the outstanding feature of this compound is the formation of Eu2+ dimers, which allows us to understand the deviation of the magnetic susceptibility χ(T) from the Curie-Weiss law below about 70 K, the field-dependent magnetization M(B) below ≈80K, and the reduced entropy at the ordering temperature S(TN)=0.64Rln(8). A significant change in the exchange interactions occurs between T≈70K (where θP=18K) and TN=13.3K (to θP=-4.5K). The strong electronic overlap, arising from the reduced Eu-Eu spacing (compared with that in pure Eu2+) is expected to favor dimer quasiparticles formation, leading to a significant change in the magnetic structure. From the analysis of the derivatives of the magnetic parameters, ∂χ/∂T and ∂M/∂B, as well as the field dependence of the specific heat and mangnetoresistance, a comprehensive magnetic phase diagram is obtained. Two critical points are recognized and a tentative description of the magnetic structures is proposed. The possible formation of a skyrmion lattice, arising from the presence of magnetically frustrated pockets in the phase diagram, is suggested by theoretical studies on hexagonal structures that exhibit similar interaction patterns.