Frustration driven magnetic states of A-site spinels probed by mu SR

• The normal A-site spinels MnAl2O4, FeAl2O4, CoAl2O4, as well as related mixed (Mn0.5Fe0.5Al2O4) and partially inverted (Fe1.4Al1.6O4) spinels have been studied by mu SR. The magnetic ions are subject to magnetic frustration by competing interactions. In all materials and at all temperatures the mu SR spectra consist of two signals suggesting a bimodal distribution of the fluctuation rates of magnetic moments. A characteristic temperature T (M) is found in each compound, representing either a magnetic phase transition into a long-range ordered state (MnAl2O4, Fe1.4Al1.6O4) or the formation of a spin liquid phase (FeAl2O4, CoAl2O4, Mn0.5Fe0.5Al2O4). The magnetic ground state of MnAl(2)O(4)aEuroEuroshows coexistence of antiferromagnetic and spin liquid phases. In FeAl(2)O(4)aEuroEuroand CoAl(2)O(4)aEuroEurolong-range order is suppressed altogether, the ground state can be characterized as a fast relaxing spin liquid coexisting with a small fraction of paramagnetic spins. The partial replacement of Mn by Fe in Mn(0.5)Fe(0.5)Al(2)O(4)aEuroEuroprevents long-range order and leads to a spin liquid state in the low temperature limit. The partial occupancy of B-sites by magnetic ions in Fe(1.4)Al(1.6)O(4)aEuroEurostrengthens the exchange coupling, allowing the formation of long-range magnetic order at a rather high temperature (similar to 100 K). Magnetic phase diagrams are presented demonstrating that for the studied compounds the magnetic properties are determined by the degree of frustration.

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NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

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Physics

Fysik

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