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This paper reports the observation of hexagonal phase of barium titanate by Mn doping and its effect on dielectric and magnetic properties. Ceramic samples of Ba 0.98 Zn 0.02 Ti 1− x Mn x O 3 (where, x = 0.04, 0.06 and 0.08) were prepared by traditional solid-state reaction route. The hexagonal phase is stabilized in the composition Ba 0.98 Zn 0.02 Ti 0.92 Mn 0.08 O 3 and a very feeble M – H loop is also observed in that composition. This induced magnetism is expected due to the exchange interactions between magnetic polarons formed by oxygen vacancies with Mn ions. The dielectric constant as well as the ferroelectric to paraelectric transition temperature is systematically decreased with increasing of Mn doping concentration. Further to that, the temperature dependent dielectric constant curve is also broadened at transition temperature with increasing of Mn concentration. However, the ferroelectric to paraelectric transition temperature is well above room temperature. [ABSTRACT FROM AUTHOR]

Ceramic samples of BaTi 0.95− x Hf 0.05 Co x O 3 (where, x =0.05, 0.1, and 0.15) were prepared through a solid state reaction route and structure, morphology, magnetic and ferroelectric properties have been investigated. Defects play a key role in influencing magnetic as well as the electric properties in the above compositions. Magnetism observed in doped compositions is significantly depended upon Co ion concentration and oxygen vacancies. With increasing of Co ion concentration, the concentration of oxygen vacancies is increased and as a result of which enhanced magnetic effect is observed. The presence of oxygen vacancy forms defect-dipoles with Co and Hf. These defect-dipoles prominently influenced the polarization and coercive field in doped compositions. Although remnant polarization is decreased noticeably in doped compositions, but the ferroelectricity is observed well above room temperature. These results clearly demonstrate the importance of the contribution of defects for observation of room temperature multiferroic properties in Co based BaTiO 3 ceramics. [ABSTRACT FROM AUTHOR]

Abstract: We report the observation of room temperature magnetism and ferroelectricity in polycrystalline BaTi0.95−x Hf0.05Co x O3 ceramics, where x=0.05, 0.1, and 0.15. Magnetic and ferroelectric hysteresis loops are strongly influenced by Co ion doping concentration. Magnetization of doped compositions is enhanced with increasing of Co ion concentration. Room temperature ferromagnetism is also observed in BaTi0.8Hf0.05Co0.15O3. Simultaneously, the saturation electric polarization value is decreased with the increasing of Co ion doping concentration. Our XPS results have revealed the presence of oxygen vacancies in doped samples. Oxygen vacancies have significant influence on magnetic and ferroelectric properties of doped BaTiO3. Observation of room temperature magnetism in our samples may be due to the exchange interactions of cobalt ions through oxygen vacancies. [Copyright &y& Elsevier]

Abstract: Cobalt (Co) doped HoMnO3 (HMO) bulk ceramics having structural formula HoMn1−x Co x O3 (x=0, 0.025, 0.05, 0.1) are prepared using a conventional solid state reaction route and the effect of Co substitution at Mn site for the improvement of its structural, dielectric and multiferroic properties is studied. Optimizing the dopant concentration of Co (x=0.1), hexagonal phase (P63cm) of HMO is completely transformed to orthorhombic (Pbnm) structure. From magnetic measurement, it is observed that incorporation of Co atoms into HMO shows low temperature ferromagnetic behavior around 10K and its origin is attributed to the double exchange interaction between Mn3+- and Mn4+ ions. The materials also exhibit a sharp dielectric anomaly well above the room temperature around 530K at the concentration of x=0.1. Shifting of both magnetic transition as well as dielectric anomaly curve towards higher temperature is a clear indication for the existence of strong correlation between magnetic and electric dipole ordering. From XPS spectrum, it is found that oxidation state of Co atoms is +2 state and Mn atoms are both in +3 and +4 mixed state. [Copyright &y& Elsevier]

Abstract: Our paper reports structural, magnetic and ferroelectric properties of Ni doped barium titanate. Ceramics samples of BaTi1−x Ni x O3 (here, x=0, 0.05, 0.1, and 0.15) were prepared through solid state sintering technique. It is revealed from structural studies that the phase transformation from tetragonal to hexagonal phase is strongly influenced by Ni doping concentration. Magnetism is induced in doped composition and the value of magnetism is dependent upon Ni ion concentration. This enhanced magnetic effect is likely to originate from carrier-mediated exchange interactions. Ferroelectricity was observed in all samples at room temperature, but it was decreased by Ni doping. [Copyright &y& Elsevier]

Polycrystalline Zn 1-x Cr x O (0.01 ≤ x ≤ 0.09) samples synthesised by solid state reaction technique were sintered at different temperatures following slow step sintering schedule, investigated for optical and magnetic properties using suitable characterisation techniques. Cr 2 O 3 and CrO 2 phases have been detected in the Raman spectra of Zn 1 -x Cr x O samples with x ≥ 0.05. Photoluminescence study indicated improved optical property of the samples compared to undoped ZnO. While low percentage Cr doped samples show diamagnetic behaviour, different types of magnetic orderings are observed in the samples with higher percentage of dopants (x ≥ 0.05) for different sintering temperatures. The spin system and magnetic properties were analysed through Electron Spin Resonance study; g-value of 1.97 indicates Cr in 3+ valence state in ZnO. Presence of both Cr3+ and Cr4+ in ZnO understood to facilitate super exchange interactions to promote room temperature ferromagnetism. ESR study ensures improved magnetic homogeneity through slow step sintering process. [ABSTRACT FROM AUTHOR]

We have optimized Gd ion substitution in BiFeO 3 (BFO) and observed prominently change in structural, electrical and magnetic behavior of Bi 1+2x Gd 2x/2 Fe 1−2x O 3 ceramics synthesized through slow step sintering schedule. It is observed that with the increase in concentration of Gd (x=0.1), original structure of BFO is transformed from rhombohedral R 3 c space group to orthorhombic Pn 21 a space group. Surprisingly, unit cell volume is drastically contracted (35% for x=0.2) and the sintered specimen showed enhanced room temperature ferromagnetic behavior although the original BFO is normally G-type antiferromagnetic in nature at 643 K. It is expected that intrinsic chemical pressure within the bulk body built by the substitution of Gd in presence of excess bismuth greatly supported through unidirectional movement of electrical dipole moment with in each individual domain as a result of which suppression of leakage current with enhanced dielectric and ferroelectric hysteresis is observed. [ABSTRACT FROM AUTHOR]