Ferromagnetic spin fluctuations in quasi-2D—EuCu9Mg2

The ternary intermetallic compound EuCu9Mg2 has been synthesized. The magnetic properties have been investigated by magnetization measurements and 151Eu Mössbauer spectroscopy. Europium is divalent and a spin freezing is observed at 25 K. However, this spin freezing is characterized by the onset of strong magnetic irreversibility, which suggests a cluster-glass freezing. The Mössbauer spectra can be analyzed as the superposition of two subspectra of Eu2+ ions, which is consistent with a cluster-glass freezing. A transition to the ferromagnetic state is induced by application of a magnetic field the order of 0.5 T. This anomalous feature is attributed to quantum spin fluctuations that oppose the long-range ferromagnetic ordering, due to the two-dimensional topology of the geometric arrangement of the Eu2+ ions. This 2D-topology is also evidenced by a quadratic variation of the specific heat as a function of temperature down to 2.7 K. The electrical resistivity is also analyzed in the framework of intermetallic compounds dominated by ferromagnetic spin fluctuations above the spin-freezing temperature.

Research highlights▶ Magnetic properties Mössbauer spectra and specific heat are consistently modeled. ▶ These properties are characteristics of a quasi-2D system. ▶ Transition to 3D long-range ferromagnetic ordering induced by the magnetic field. ▶ Investigation of inhomogeneous and progressive spin freezing upon cooling at small field, in relation to the 2D-character, by both the static and the dynamic magnetic properties, and Mössbauer spectroscopy.