Magnetic field-induced dielectric hole burning in Mn-doped SrTiO₃

In Sr_0.98Mn_0.02TiO₃, successive spin (~34K) and structural glass (T_g~38K) transitions were previously found. The leading cause of magneto-electricity is the biquadratic coupling between antiferroelectrically paired dipoles (created by the off-centered occupation of Mn at Sr sites) with their corresponding antiferromagnetically paired Mn²⁺ spins. Here, to investigate the glassy magneto-electric correlation, the electrical third harmonic (|ε₃|) permittivity—the instantaneous dipolar response —has been measured across T_g by two ac field excitations, 1.4 and 4.2 kVm^-1, and each ac field measurement was performed under constant magnetic fields 0 T, 0.1 T, and 4.0 T. For this purpose, first, ac field-induced change is calculated for a particular magnetic field as δ|ε₃|_xT= (|ε₃|_4.2kV/m-|ε₃|_1.4kV/m)/|ε₃|_1.4kV/m, where x=0,0.1,4.0. Then the magneto-capacitance change is calculated as, Δ|ε₃|_xT= (δ|ε₃|_xT-δ|ε₃|_0T)/δ|ε₃|_0T, where x=0.1,4.0. Below the T_g, Δ|ε₃|_xT spectra show an anomaly in the 40-80 kHz range, especially for 0.1 T. The anomaly in Δ|ε₃|_xT spectra indicates the heterogeneous energy absorption by the biquadratically coupled spins and dipoles from the higher electric field is significantly influenced by the applied magnetic fields below the T_g.