Evidences for magnetic dimers and skyrmion lattice formation in Eu$_2$Pd$_2$Sn

TL;DR

This study revisits the magnetic, thermal, and transport properties of Eu$_2$Pd$_2$Sn, revealing Eu$^{2+}$ dimer formation, complex magnetic phase behavior, and suggesting the possible emergence of a skyrmion lattice due to magnetic frustration.

Contribution

It provides new measurements and analysis indicating Eu$^{2+}$ dimer formation and proposes the potential existence of a skyrmion lattice in Eu$_2$Pd$_2$Sn, a non-centrosymmetric compound.

Findings

Eu$^{2+}$ dimers form in the paramagnetic phase.

Complex magnetic phase diagram with two critical points.

Possible skyrmion lattice formation suggested by phase diagram analysis.

Abstract

Magnetic, thermal and transport properties of the non-centrosymmetric compound Eu$_2$Pd$_2$Sn are revisited after including new measurements. In its paramagnetic phase, the outstanding feature of this compound is the formation of Eu$^{2+}$ dimers that allows to understand the deviation of the magnetic susceptibility $\chi(T)$ from the C-W law below about 70\,K, the field dependent magnetization $M(B)$ variation below $\approx 80$\,K and the reduced entropy at the ordering temperature $S(T_N)= 0.64R\ln(8)$. A significant change of the exchange interactions occurs between $T\approx 70$\,K (where $\theta_P = 18$\,K) and $T_N = 13.3$\,K (where $\theta_P =-4.5$\,K). The strong electronic overlap, arising from the reduced Eu-Eu spacing compared with that of pure Eu$^{2+}$ is expected to power these quasiparticles formation, inducing a significant reformulation of the magnetic structure. A rich magnetic phase diagram is obtained from the analysis of the derivatives of the magnetic parameters: $\partial \chi/\partial T$ and $\partial M/\partial B$, and the field dependence of the specific heat. Two critical points are recognized and a tentative description of the magnetic structures is proposed. The possible formation of a skyrmion lattice, that arises from the presence of magnetically frustrated pockets in the phase diagram, is suggested by theoretical studies on hexagonal structures exhibiting similar interactions pattern.