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Register a new userReversible room-temperature ferromagnetism in Nb-doped SrTiO3 single crystals
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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.
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We investigated the reversible ferromagnetic (FM) behavior of pure and Co doped CeO2 nanopowders. The as-sintered samples displayed an increasing paramagnetic contribution upon Co doping. Room temperature FM is obtained simply by performing thermal treatments in vacuum at temperatures as low as 500^{circ}C and it can be switched off by performing thermal treatments in oxidizing conditions. The FM contribution is enhanced as we increase the time of the thermal treatment in vacuum. Those systematic experiments establish a direct relation between ferromagnetism and oxygen vacancies and open a path for developing materials with tailored properties.
Ab initio studies have theoretically predicted room temperature ferromagnetism in crystalline SnO2, ZrO2 and TiO2 doped with non magnetic element from the 1A column as K and Na. Our purpose is to address experimentally the possibility of magnetism in both Sn1-xKxO2 and Sn1-xCaxO2 compounds. The samples have been prepared using equilibrium methods of standard solid state route. Our study has shown that both Sn1-xCaxO2 and Sn1-xKxO2 structure is thermodynamically unstable and leads to a phase separation, as shown by X-ray diffraction and detailed micro-structural analyses with high resolution transmission electron microscopy (TEM). In particular, the crystalline SnO2 grains are surrounded by K-based amorphous phase. In contrast to Ca: SnO2 samples we have obtained a magnetic phase in K: SnO2 ones, but no long range ferromagnetic order. The K: SnO2 samples exhibit a moments of the order of 0.2 {mu}B/K /ion, in contrast to ab-initio calculations which predict 3{mu}B, where K atoms are on the Sn crystallographic site. The apparent contradictions between our experiments and first principle studies are discussed.
Atomically thin transition metal dichalcogenide (TMD) semiconductors hold enormous potential for modern optoelectronic devices and quantum computing applications. By inducing long-range ferromagnetism (FM) in these semiconductors through the introduction of small amounts of a magnetic dopant, it is possible to extend their potential in emerging spintronic applications. Here, we demonstrate light-mediated, room temperature (RT) FM, in V-doped WS2 (V-WS2) monolayers. We probe this effect using the principle of magnetic LC resonance, which employs a soft ferromagnetic Co-based microwire coil driven near its resonance in the radio frequency (RF) regime. The combination of LC resonance with an extraordinary giant magneto-impedance effect, renders the coil highly sensitive to changes in the magnetic flux through its core. We then place the V-WS2 monolayer at the core of the coil where it is excited with a laser while its change in magnetic permeability is measured. Notably, the magnetic permeability of the monolayer is found to depend on the laser intensity, thus confirming light control of RT magnetism in this two-dimensional (2D) material. Guided by density functional calculations, we attribute this phenomenon to the presence of excess holes in the conduction and valence bands, as well as carriers trapped in the magnetic doping states, which in turn mediates the magnetization of the V-WS2 monolayer. These findings provide a unique route to exploit light-controlled ferromagnetism in low powered 2D spintronic devices capable of operating at RT.
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.
We prove a spontaneous magnetization of the oxygen-terminated ZnO (0001) surface by utilizing a multi-code, SIESTA and KKR, first-principles approach, involving both LSDA+U and selfinteraction corrections (SIC) to treat electron correlation effects. Critical temperatures are estimated from Monte Carlo simulations, showing that at and above 300 K the surface is thermodynamically stable and ferromagnetic. The observed half-metallicity and long-range magnetic order originate from the presence of p-holes in the valence band of the oxide. The mechanism is universal in ionic oxides and points to a new route for the design of ferromagnetic low dimensional systems.
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