Ferroic superglasses: Relaxor ferroelectrics PMN and SBN vs. CoFe superspin glass

AbstractRandom electric fields (RF) due to charge disorder are at the origin of polar nanoregions (PNR) in the cubic relaxor PbMg1/3Nb2/3O3. They initiate Lacroix-Bene-type Cole-Cole semicircles, which achieve Cole-Davidson skew and dynamic power law criticality upon approaching superdipolar glass freezing. Below Tg ≈ 240 K percolation of PNR into microdomains is evidenced by interfacial creep and relaxation via Cole-Cole diagrams. Similar behavior occurs in uniaxial Sr0.8Ba0.2Nb2O6 (Tg ≈ 301 K). In contrast, matrix isolated ferromagnetic nanoparticles in CoFe/Al2O3 multilayers without RF interaction lack all of these effects except superglassy critical dynamics at Tg ≈ 46 K.