Abstract
We report the results of measurements of the low-temperature specific heat Cp(T) and the ac susceptibility χac(T) in low applied magnetic fields for a series of samples of Eu1-xCaxB6. The anomalies in Cp(T), together with the results for χac(T) and M(H), confirm the onset of phase transitions to long range magnetic order for x < 0.7 and provide evidence that for x ≥ 0.7, the Eu moments, which are captured in large magnetic clusters with magnetic moments of the order of 260 μB, adopt a spin-glass type ground state. The data set allows to establish the low-temperature [ T,x] phase diagram of this alloy series.
Highlights
The phenomenon of magnetic order in solids is most often based on periodic arrays of magnetic moments on regular lattice sites, here denoted as magnetic sites, of the crystal structure of the respective material
The Eu ions, each carrying a magnetic moment of 7 μB due to the half filled S = 7/2 4f electron shell [3], occupy the centers of cubes whose corners are decorated with B6 octahedra
In summary we provide experimental evidence that for x > 0.7 and below the site percolation limit, the magnetic ground state of Eu1−xCaxB6 is reached via the freezing of moments of sizable Eu-rich clusters
Summary
The phenomenon of magnetic order in solids is most often based on periodic arrays of magnetic moments on regular lattice sites, here denoted as magnetic sites, of the crystal structure of the respective material. The present work is devoted to investigating the influence of the random removal of magnetic moments on the onset of magnetic order at low temperatures. The hexaboride compound EuB6 may be regarded as a model system for studying this site percolation problem. It crystallizes with a simple cubic structure. The chemical composition may be changed by, e.g., replacing the rare-earth element Eu by the alkaline earth element Ca. The chemical composition may be changed by, e.g., replacing the rare-earth element Eu by the alkaline earth element Ca Because both type of ions adopt a divalent configuration, the substitution is in first order expected to be isoelectronic and provoking a dilution of magnetic moments. Published results of electronic transport measurements and their interpretation based on theoretical modelling suggested the influence of site percolation on the magnetic and transport properties of Eu1−xCaxB6 [4]. The reader should consult ref erences [4,8,14]
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