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Register a new userMagnetic field tuning of polaron losses in Fe doped BaTiO3 single crystals
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Artificial tuning of dielectric parameters can result from interface conductivity in polycrystalline materials. In ferroelectric single crystals, it was already shown that ferroelectric domain walls can be the source of such artificial coupling. We show here that low temperature dielectric losses can be tuned by a dc magnetic field. Since such losses were previously ascribed to polaron relaxation we suggest this results from the interaction of hopping polarons with the magnetic field. The fact that this losses alteration has no counterpart on the real part of the dielectric permittivity confirms that no interface is to be involved in this purely dynamical effect. The contribution of mobile charges hopping among Fe related centers was confirmed by ESR spectroscopy showing maximum intensity at ca Tsim40 K.
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Simultaneous co-existence of room-temperature(T) ferromagnetism and ferroelectricity in Fe doped BaTiO$_3$ (BTO) is intriguing, as such Fe doping into tetragonal BTO, a room-T ferroelectric (FE), results in the stabilization of its hexagonal polymorph which is FE only below $sim$80K. Here, we investigate its origin and show that Fe-doped BTO has a mixed-phase room-temperature multiferroicity, where the ferromagnetism comes from the majority hexagonal phase and a minority tetragonal phase gives rise to the observed weak ferroelectricity. In order to achieve majority tetragonal phase (responsible for room-T ferroelectricity) in Fe-doped BTO, we investigate the role of different parameters which primarily control the PE hexagonal phase stability over the FE tetragonal one and identify three major factors namely, the effect of ionic size, Jahn-Teller (J-T) distortions and oxygen vacancies (OVs), to be primarily responsible. The effect of ionic size which can be qualitatively represented using the Goldschmidts tolerance (GT) factor seems to be the major dictating factor for the hexagonal phase stability. The understanding of these factors not only enables us to control them but also, achieve suitable co-doped BTO compound with enhanced room-T multiferroic properties.
The search for oxide-based room-temperature ferromagnetism has been one of the holy grails in condensed matter physics. Room-temperature ferromagnetism observed in Nb-doped SrTiO3 single crystals is reported in this Rapid Communication. The ferromagnetism can be eliminated by air annealing (making the samples predominantly diamagnetic) and can be recovered by subsequent vacuum annealing. The temperature dependence of magnetic moment resembles the temperature dependence of carrier density, indicating that the magnetism is closely related to the free carriers. Our results suggest that the ferromagnetism is induced by oxygen vacancies. In addition, hysteretic magnetoresistance was observed for magnetic field parallel to current, indicating that the magnetic moments are in the plane of the samples. The x-ray photoemission spectroscopy, the static time-of-flight and the dynamic secondary ion mass spectroscopy and proton induced x-ray emission measurements were performed to examine magnetic impurities, showing that the observed ferromagnetism is unlikely due to any magnetic contaminant.
Fe doping into BaTiO3, stabilizes the paraelectric hexagonal phase in place of the ferroelectric tetragonal one [P. Pal et al. Phys. Rev. B, 101, 064409 (2020)]. We show that simultaneous doping of Bi along with Fe into BaTiO3 effectively enhances the magnetoelectric (ME) multiferroic response (both ferromagnetism and ferroelectricity) at room-temperature, through careful tuning of Fe valency along with the controlled-recovery of ferroelectric-tetragonal phase. We also report systematic increase in large dielectric constant values as well as reduction in loss tangent values with relatively moderate temperature variation of dielectric constant around room-temperature with increasing Bi doping content in Ba1-xBixTi0.9Fe0.1O3 (0<x<0.1), which makes the higher Bi-Fe codoped sample (x=0.08) promising for the use as room-temperature high-k dielectric material. Interestingly, x=0.08 (Bi-Fe codoped) sample is not only found to be ferroelectrically (~20 times) and ferromagnetically (~6 times) stronger than x=0 (only Fe-doped) at room temperature, but also observed to be better insulating (larger bandgap) with indirect signatures of larger ME coupling as indicated from anomalous reduction of magnetic coercive field with decreasing temperature. Thus, room-temperature ME multiferroicity has been engineered in Bi and Fe codoped BTO (BaTiO3) compounds.
The magnetic properties of two-dimensional VI3 bilayer are the focus of our first-principles analysis, highlighting the role of trigonal crystal-field effects and carried out in comparison with the CrI3 prototypical case, where the effects are absent. In VI3 bilayers, the empty a1g state - consistent with the observed trigonal distortion - is found to play a crucial role in both stabilizing the insulating state and in determining the inter-layer magnetic interaction. Indeed, an analysis based on maximally localized Wannier functions allows to evaluate the interlayer exchange interactions in two different VI3 stackings (labelled AB and AB), to interpret the results in terms of virtual-hopping mechanism, and to highlight the strongest hopping channels underlying the magnetic interlayer coupling. Upon application of electric fields perpendicular to the slab, we find that the magnetic ground-state in the AB stacking can be switched from antiferromagnetic to ferromagnetic, suggesting VI3 bilayer as an appealing candidate for electric-field-driven miniaturized spintronic devices.
Room temperature ferromagnetism was observed in n-type Fe-doped In2O3 thin films deposited on c-cut sapphire substrates by pulsed laser deposition. Structure, magnetism, composition, and transport studies indicated that Fe occupied the In sites of the In2O3 lattice rather than formed any metallic Fe or other magnetic impurity phases. Magnetic moments of films were proved to be intrinsic and showed to have a strong dependence on the carrier densities which depended on the Fe concentration and its valance state as well as oxygen pressure.
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