Origin of magnetovolume effect in a cobaltite

The layered perovskite ${\mathrm{PrBaCo}}_{2}{\mathrm{O}}_{5.5+x}$ demonstrates a strong negative thermal expansion (NTE) which holds potential for being fabricated into composites with zero expansion. NTE was found to be intimately associated the spontaneous magnetic ordering, known as magnetovolume effect (MVE). Here we report compelling evidence that continuouslike MVE in is intrinsically of discontinuous character, originating from magnetoelectric transition an antiferromagnetic insulating large-volume (AFILV) phase ferromagnetic less-insulating small-volume (FLISV) phase. Furthermore, (ME) shows high sensitivity multiple external stimuli such temperature, carrier doping, hydrostatic pressure, field, etc. In contrast well-known ME colossal magnetoresistance and multiferroic involve symmetry breaking crystal structure, cobaltite purely isostructural. Our discovery provides pathway realizing well NTE, may find applications new techniques.