Spin glass behaviour in an antiferromagnetic non-frustrated lattice: Sr2FeNbO6perovskite

Investigation of new magnetoelastic and magnetic transitions accompanied with magnetoelectric coupling in [Formula: see text] multiferroic

A new multiferroic solid solution [Formula: see text] has been developed and characterized for structure, phase transition, magnetoelectric and magnetoelastic coupling. Temperature dependent measurement of dc-magnetization [Formula: see text] on [Formula: see text] ceramic shows two magnetic transitions one around [Formula: see text]42 K and the second at [Formula: see text]130 K. The real part of dielectric permittivity exhibits step like change at the magnetic anomaly temperature ([Formula: see text]130 K) which indicates the presence of magnetoelectric coupling. The change in the value of dielectric permittivity on the application of magnetic field confirms the presence of magnetoelectric coupling in [Formula: see text] ceramic. The room temperature polarization (P)-electric field (E) hysteresis loop measurement shows week ferroelectric nature of sample while the magnetization (M) versus magnetic field (H) measurement suggest weakly ferromagnetic character. The ferroelectric nature of sample was further confirmed by calculating remanent polarization using PUND measurement. The Rietveld structural analysis of low temperature x-ray powder diffraction data does not reveal any crystallographic phase transition in terms of peak splitting or new reflections. However, temperature dependence of lattice parameters, tetragonality, unit cell volume, [Formula: see text] octahedral tilt angle ([Formula: see text]), [Formula: see text] bond length and [Formula: see text] bond angles reveal discontinuous changes at both the magnetic transitions observed in temperature dependence of magnetization. This confirms that both the magnetic anomalies (around [Formula: see text]42 K and [Formula: see text]130 K) exhibit magnetoelastic coupling accompanied with isostructural transitions.

Structural manipulation and tailoring of dielectric properties in SrTi1-xFexTaxO3 perovskites: Design of new lead free relaxors

We report composition dependent structure evolution from SrTiO3 to SrFe0.5Ta0.5O3 by powder X-ray and neutron diffraction studies of SrTi1-2xFexTaxO3 (0.00 ≤ × ≤ 0.50) compositions. Structural studies reveal cubic (Pm3m) perovskite-type structure of the parent SrTiO3 for x up to 0.075 and cation disordered orthorhombic (Pbnm) perovskite-type structure for x ≥ 0.33. A biphasic region consisting of a mixture of cubic and orthorhombic structures is found in the range for 0.10 ≤ × ≤ 0.25. Dielectric studies reveal transformation from a normal dielectric to relaxor like properties with increasing Fe(3+) and Ta(5+) concentration. Dielectric response is maximum at x = 0.33 in the series. The results establish a protocol for designing new lead-free relaxor materials based on the co-substitution of Fe(3+) and Ta(5+) for Ti(4+) in SrTiO3. A complex interplay of strain effects arising from distribution of cations at the octahedral sites of the perovskite structure controls the dielectric properties.

Low-Temperature Magnetic Behavior of Perovskite Compounds PbFe1/2Ta1/2O3 and PbFe1/2Nb1/2O3

The isostructural perovskite compounds PbFe(1/2)Ta(1/2)O3 and PbFe(1/2)Nb(1/2)O3 have been known for long time, and they are part of the important class of materials called multiferroic, where ferroelasticity, ferroelectricity, and ferromagnetism coexist. In the literature regarding PbFe(1/2)Ta(1/2)O3 and PbFe(1/2)Nb(1/2)O3, an "anomaly" of their low-temperature magnetic behavior has not always been reported. Moreover, both the origin of this behavior, and the cause for which it was not always observed, were never completely explained. In this paper, the magnetic behavior of the two compounds at low temperature has been extensively studied and explained as the occurring of a spin-glasslike transition.