Abstract

Magnetization M(T,B), specific heat cp(T), and electrical resistivity ρ(T,B) show ferromagnetic ordering in Eu2CuSi3 single crystals below the Curie temperature TC=34 K. Temperature T and magnetic field B-dependent M(T,B) data give evidence for a sizable magnetic anisotropy in the AlB2-derived hexagonal structure at T<TC. The increase in |dM/dT| at TC for B=50 mT along the easy magnetic c axis (⟨001⟩) is more than twice as large as for B along the a axis (⟨010⟩). The analysis of cp(T) in the magnetically ordered phase reveals signatures of a spin-reorientation process at T≈10 K below which the magnetic anisotropy in M(T,B) almost vanishes. Measurements of electron-spin resonance (ESR) on Eu2+ ions reveal the anisotropy of the resonance field and the additional narrowing of the ESR signal at T<100 K that prove appreciable short-range ferromagnetic correlations far above TC. These lead to a large negative magnetoresistance observed in the ρ(T,B) measurements even up to a temperature T≈100 K. Below 50 K the ESR line starts to split due to the emergence of two magnetically nonequivalent Eu sites. The onset of magnetic order is manifested in the ESR spectrum by nucleation of a third line. Below T≈10 K, where thermodynamic data suggest a transformation of the ordered spins to a state with strongly reduced anisotropy, the ESR spectrum evolves into a featureless broad asymmetric peak.

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