A relaxor ferroelectric consists of many polar nanoregions that only give rise to a net electric dipole moment when the polar nanoregions are co-aligned using an external electric field. In the double perovskite La3Ni2SbO9 we found the magnetic equivalent of a relaxor ferroelectric as long-range magnetic order only occurs on the application of a magnetic field. In our quest to understand what factors are key in determining whether relaxor ferromagnetism occurs we have synthesised a series of Cr-containing AA’2Cr2BO9 perovskites. This was to enable us to study the effect on the magnetic properties of changing the superexchange pathway from being σ-mediated in La3Ni2SbO9 to being π-mediated in AA’2Cr2BO9 . Here we present the results of powder x-ray and neutron diffraction, electron microscopy and SQUID magnetometry measurements on LaSr2Cr2SbO9 and PrSr2Cr2BO9 (B=Sb, Ta, Nb). Both LaSr2Cr2SbO9 and PrSr2Cr2SbO9 appear to order ferrimagnetically below ~150 K whereas PrSr2Cr2NbO9 and PrSr2Cr2TaO9 display magnetic properties more akin to a spin glass with two magnetic transitions evident at 150 K and 20 K.

Moving beyond La3Ni2SbO9: The search for relaxor ferromagnetism in LaSr2Cr2SbO9 and PrSr2Cr2BO9 (B=Sb, Ta, Nb)

254th National Meeting (2017)

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