Magnetism of frustrated A-site spinels

Abstract: In the A-site spinels (, Fe, Co) the A-site sublattice is subjected to strong frustration, putting all three compounds on the verge between long-range and short-range magnetic order. The spectra of the three compounds show two signals at all temperatures examined and a dramatic change in spectral shape at characteristic temperatures. Above this temperature, one signal (slowly relaxing) is typical for free paramagnetic spins, the other (fast relaxing) for highly correlated paramagnetic spins. For the ratio of their intensities is 1:3 independent of temperature and the spectral change occurs around 40K ( from neutron data) where the strongly correlated fraction enters into long-range order and the free paramagnetic fraction into a glassy spin state. For or Fe, the free paramagnetic fraction increases from to 85% with rising temperature. At the cusp temperatures observed in magnetization (5 or 12K) the dominating, highly correlated paramagnetic fraction turns into a dynamic short-range ordered magnetic ground state. In all three compounds substantial local spin disorder and persistent spin fluctuations characterize their magnetic ground states, typical features of highly frustrated magnets. [Copyright &y& Elsevier]