Magnetization $M\left(T,B\right)$, specific heat $c_{\text{p}}\left(T\right)$, and electrical resistivity $\rho \left(T,B\right)$ show ferromagnetic ordering in ${\text{Eu}}_2{\text{CuSi}}_3$ single crystals below the Curie temperature $T_{\text{C}}=34\text{K}$. Temperature $T$ and magnetic field $B$-dependent $M\left(T,B\right)$ data give evidence for a sizable magnetic anisotropy in the ${\text{AlB}}_2$-derived hexagonal structure at $T<T_{\text{C}}$. The increase in $\left|dM/dT\right|$ at $T_{\text{C}}$ for $B=50\text{mT}$ along the easy magnetic $c$ axis $\left(⟨001⟩\right)$ is more than twice as large as for $B$ along the $a$ axis $\left(⟨010⟩\right)$. The analysis of $c_{\text{p}}\left(T\right)$ in the magnetically ordered phase reveals signatures of a spin-reorientation process at $T\approx 10\text{K}$ below which the magnetic anisotropy in $M\left(T,B\right)$ almost vanishes. Measurements of electron-spin resonance (ESR) on ${\text{Eu}}^{2+}$ ions reveal the anisotropy of the resonance field and the additional narrowing of the ESR signal at $T<100\text{K}$ that prove appreciable short-range ferromagnetic correlations far above $T_{\text{C}}$. These lead to a large negative magnetoresistance observed in the $\rho \left(T,B\right)$ measurements even up to a temperature $T\approx 100\text{K}$. 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 $T\approx 10\text{K}$, 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.

• Received 19 November 2009

DOI:https://doi.org/10.1103/PhysRevB.82.134446