Topological spin dynamics in Eu doped SnTe using spin resonance and magnetic measurements

Abstract

Topological materials offer a rich platform to explore exotic quantum states, such as topological Hall and axion-insulator phases. The topological crystalline insulator (TCI) SnTe exhibits weak antilocalization (WAL) along with parabolic bulk magnetoconductance (MC), primarily due to a high density of intrinsic Sn vacancies ( 10²¹/cm³). In this study, WAL signals were observed via electron spin resonance (ESR) in deformed disc-shaped SnTe nanoparticles (5–50 nm), indicating anisotropic spin dynamics. Eu doping in SnTe NPs increases the Sn vacancy formation energy, reducing the overall vacancy concentration. It also suppresses bulk MC through temperature and charge-transfer-driven hole localization in bound magnetic polarons (BMPs). This increases the observability of the WAL effect. Defect and impurity-induced stress introduce scalar perturbative potentials (u), breaking electron–hole symmetry and enabling spin-independent electron scattering. Simultaneously, magnetic proximity coupling from Eu³⁺ ions hybridized Te 5p, Sn 5p, 4d, and Eu 4d orbitals and split them into singlet(p_z), doublet (p_x, p_y and E_g), and triplet (t_2g) components, respectively. This interaction, described by the magnetic scattering vector (m), scatters the spin of itinerant carriers through localized moments, leading to competing canted AFM and FM RKKY interactions. A magnetic field–dependent spin-flop transition of Eu3+ spins within host TCI SnTe is evident in the anomalous M–H curves and AC susceptibility at low temperatures (2.9 K). These anomalous magnetic behaviors of the Eu³⁺ spin, magnetic anisotropy energy, along with SOC induced spin canting and charge transfer among Eu, Sn, Te, and Sn vacancies, are further supported by density functional theory (DFT) computation.