Unveiling quantum superparamagnetism by interacting monodomains in multiferroic Er-doped bismuth ferrate nanostructured particles

Abstract

In the last few years, the quantum superparamagnetic (QSP) phenomenon has been reported in isolated ultrasmall nanoparticles. In this work, a QSP state and superparamagnetic (SP) state in nanostructured Er-doped BiFeO3 particles, attributed to the Bi substitution by Er, that leads to structural distortion and the growth of single-phase ferromagnetic nano-monodomains with critical size, are discussed. A systematic study of the structural and magnetic properties of the Bi1–xErxFeO3 (0.0 ≤ x ≤ 0.12) nanostructured particles obtained by the sol–gel route is presented. Rietveld refinement and Raman spectroscopy analysis revealed structure distortions with Er incorporation, and the nanostructured nature of the samples is demonstrated by transmission electron microscopy. For x = 0.04 and 0.08, the zero-field cooled and field cooled magnetization analysis reveals a SP behavior at room temperature while, at cryogenic temperatures, a magnetic phase transition from a blocked SP state to a QSP state through quantum tunneling of magnetization takes place. Such phenomena are regulated by the interaction between the spin-glass surface layer at the boundaries of the monodomains. For x = 0.12, an anomalous transition from paramagnetic to QSP states was observed. Such SP behaviors have great potential for developing high-performance thermoelectrical materials, magnetoelectric devices, and biomedical applications.