The compound, Fe 2 TiO 5 (FTO) is a well-known uniaxial anisotropic spin-glass insulator with two successive glassy freezing temperatures i.e. transverse (T TF = 9K) and longitudinal (T LF = 55 K). In this article, we present the results of measurements of complex dielectric behavior, electric polarization as a function of temperature (T), in addition to characterization by magnetic susceptibility and heat-capacity, primarily to explore magnetoelectric (ME) coupling and multiglass properties in uniaxial anisotropic spin cluster-glass FTO. The existence of two magnetic transitions is reflected in the isothermal magnetodielectric (MD) behavior in the sense that the sign of MD is different in the T regime TT TF . The data in addition provide evidence for the glassy dynamics of electric-dipoles; interestingly, this occurs at much higher temperature (~100-150 K) than T LF with high remnant polarization at 10 K ( 4000C/m 2 ) attributable to short-range magnetic correlations, thereby offering a route to attain ME coupling above 77 K.
We have investigated the complex dielectric and impedance properties of magnetoelectric compound Fe 2 TiO 5 (FTO) as a function of temperature (T) and frequency (f) to understand the grain (G) and grain boundary (G b ) contributions to its dielectric response.The temperature and frequency dependent dielectric permittivity (') data shows a sharp increase in permittivity above 200K accompanied with a frequency dependent peak in tan.At T<175K, only G contribution dominates even at lower frequency (~100Hz), but for T175K, the G b contribution starts appearing at low frequency. The value of critical frequency distinguishing these two contributions increases with increasing temperature. The observed non-Debye dielectric relaxation follows thermally activated process and is attributed to polaron hopping. Further the frequency dependence of ac conductivity follows the Jonscher's power-law. The temperature dependency of critical exponent 's' shows that the correlated barrier hopping model is appropriate to define the conductivity mechanism of FTO in the studied temperature regime.
Low-frequency dielectric relaxation in BaTiO3 (BTO) ceramics has been studied under the applied and dc-field cooled conditions in the frequency domain spanning from 5 mHz to 20 kHz in the temperature range of 85 K to 430 K. We observe the coexistence of broad as well as sharp maxima in the dielectric loss (tanδ) across each of the three phase transitions. The broad tanδ maxima were found to shift to higher temperatures at higher frequencies following Arrhenius behaviour with activation energies ranging from 0.18 eV to 0.23 eV. Each of the tan δ maxima slowly merged and finally vanished above the corresponding phase transitions. Both the permittivity and the tanδ loss were found to suppress and shift towards lower frequencies as a function of applied dc-field and dc-field cooled conditions. This has been attributed to the relaxation of the mesoscopic ferroelectric sub-domains/domain boundaries forming and rearranging differently across each phase transition in BTO. We also observe low-frequency relaxation above the Curie temperature. Arrhenius analysis owes its origin to the space-charge relaxation across the barrier layer formed between the electrode and the sample. The broad relaxation maxima in the tetragonal regime appear to be due to sub-domain polar-regions, which might appear due to the atomic-level mismatch of the accommodation strain appearing during tet-cubic martensitic phase transition. These regions further reform across the successive tet-ortho and ortho-rhombo phase transitions giving rise to corresponding relaxation maxima.
Tunability of the partially ordered double perovskite (PODP) and coexisting spinglass phase in SrMn1-xWxO3 (x=0.20 to 0.40) have been studied using neutron powder diffraction (NPD), muon spin relaxation (SR), and magnetic susceptibility (measurements. Structural studies reveal that SrMn1-xWxO3 undergoes a quasicontinuous transformation from simple perovskite (Pm-3m) to PODP (P21/n) phase as x increases. dc and ac measurements show a sharp cusp-like peak at a spin glass transition, Tg. The muon relaxation rate (λ) peaks at Tg following a critical growth, given by λ=λ (0).t -w [t=(T-Tg)/Tg]. However, no long-range magnetic order is observed in NPD below Tg. These measurements confirm a tunable spin-glass freezing in SrMn1-xWxO3 with Tg monotonously decreasing with W content, which we attribute to tuning the relative concentration of the coexisting Mn-O-Mn and Mn-O-W-O-Mn anti-ferromagnetic super-exchange pathways altering the geometric frustration.
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