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

Abstract

Random electric fields (RF) due to charge disorder are at the origin of polar nanoregions (PNR) in the cubic relaxor PbMg_1/3Nb_2/3O₃. They initiate Lacroix-Béné-type Cole-Cole semicircles, which achieve Cole-Davidson skew and dynamic power law criticality upon approaching superdipolar glass freezing. Below T_g ≈ 240 K percolation of PNR into microdomains is evidenced by interfacial creep and relaxation via Cole-Cole diagrams. Similar behavior occurs in uniaxial Sr_0.8Ba_0.2Nb₂O₆ (T_g ≈ 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 T_g ≈ 46 K.

KEYWORDS:

• Relaxor ferroelectrics
• random fields
• polar nanoregions
• dynamic criticality
• superdipolar glass
• percolation
• interfacial creep
• segmental relaxation

Acknowledgment

Thanks are due to Seweryn Miga for his assistance in the dielectric measurements.

Funding

The work at Katowice was supported by the Polish Ministry of Science and Higher Education under the project “Magnetic and ferroelectric multifunctional materials for electronics”.