Harmonic magneto-dielectric study in doped-, double-, and layered-perovskites

Abstract

Fundamental and harmonic magneto-dielectricity studied for varied perovskite systems--Pb 0.98 Gd 0.02 (Mg 1/3 Nb 2/3 ) 0.995 O 3 (A-site co-doped PGMN magneto-relaxor), La 0.95 Ca 0.05 CoO 3 (A-site doped spin-state LCCO), and La 2 NiMnO 6 (double-perovskite LNMO multiglass) characterize intricately polarized phases. First-harmonic signal (ε 2 ʹ) of magnetically co-doped PGMN manifests finite polarization P(H) below 270K, corroborated by the measured remnant P-E traces. Second-harmonic (ε 3 ʹ) reveals the effect of random E-fields causing electrical vitreousity, latter indicated by the divergent timescale of the fundamental response. LCCO features mixed-dipoles phase over appreciable temperature window, affiliated to the coexistent lowspins (LS) and intermediate-spins (IS). Across the 65K-start of IS-to-LS state transition (SST), dc-and acconductivities of LCCO exhibit mechanism-changeovers whereas the harmonic susceptibilities evidence IS/LS-interfacial hyper-polarizations. Below the 30K-end of SST, harmonics corroborate the vitreous phase of dipoles in the LS-matrix state. In the LNMO, positive and negative (dual) magneto-dielectricity observed is respectively attributed to the charge-hopping between Ni 2+ and Mn 4+ ions and the interfacial polarization. Second-harmonic signal here also features dispersion corresponding to the activation energy required for the electron transfer between Ni-and Mn-cations. Results from three different perovskite systems signify the combined importance of first-and second-harmonics, for a detailed understanding of electrical configurations.close to the exchange energy, stabilizing the low-spin (LS) state with configuration. HS and IS states accompany Jahn-Teller monoclinic distortions in the parent rhombohedral structure [16]. Across the IS-LS spin state transition, study of the stretching modes via Raman spectra, corresponding to different spin states, confirmed the gradual change from one spin state to another, and their coexistence over a temperature window corresponds to an order of magnitude dispersive change in the dielectric properties [16]. This vast change is traced to a mixed electrical state, comprising of phase-coexistent dipoles affiliated to the respective spin-states [17]. Thus, the system qualifies for the dielectric study of the bulk electrical-interface, as the inter-domain region between two simpler electrical mediums is well-acknowledged for device applications, because it cohosts the properties of both the media [18]. Analogous to the magneto-electricity in the composites, bulkinterfaces with no centrosymmetry in structurally single-phase materials can feature properties that are absent in the respective pure bulk media. Interestingly, La-site doping has evidenced intrinsic magnetic phase separation (magnetic glass, ferromagnetic clusters), which mandates further exploration [19]. In this regard 5% Ca-doped La 0.95 Ca 0.05 CoO 3 (LCCO) is chosen for the present study. This system has been studied in literature with signatures of SST in the dielectric properti...