Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userEmergence of Ferromagnetism Through the Metal-Insulator Transition in Undoped Indium Tin Oxide Films
72
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present a detailed study of the emergence of bulk ferromagnetism in low carrier density samples of undoped indium tin oxide (ITO). We used annealing to increase the density of oxygen vacancies and change sample morphology without introducing impurities through the metal insulator transition (MIT). We utilized a novel and highly sensitive Corbino-disk torque magnetometry technique to simultaneously measure the thermodynamic and transport effects of magnetism on the same sample after successive annealing. With increased sample granularity, carrier density increased, the sample became more metallic, and ferromagnetism appeared as resistance approached the MIT. Ferromagnetism was observed through the detection of magnetization hysteresis, anomalous Hall effect (AHE), and hysteretic magnetoresistance. A sign change of the AHE as the MIT is approached may elucidate the interplay between the impurity band and the conduction band in the weakly insulating side of the MIT.
rate research
Read More
Tin doped indium oxide (ITO) thin films are being used extensively as transparent conductors in several applications. In the present communication, we report the electrical transport in DC magnetron sputtered ITO thin films in low temperatures (25-300 K). The low temperature Hall effect and resistivity measurements reveal that the ITO thin films are moderately dis-ordered (kfl~1) and degenerate semiconductor. The transport of charge carriers in these disordered ITO thin films takes place via the de-localized states. The disorder effects lead to the well- known metal-insulator transition; this transition is observed at 110 K in ITO thin films. The metal-insulator behaviour is explained by the quantum correction to the conductivity (QCC); this approach is based on the quantum-mechanical interference effects in the disordered systems. The insulating behaviour is attributed to the combined effect of the weak localization and the electron-electron interactions.
Magnetic and magnetotransport properties of oriented polycrystalline Pr0.58Ca0.42MnO3 thin films prepared in flowing oxygen and air ambient has been investigated. The magnetic ground state of both the films is a frozen cluster glass. In the air annealed film charge order (CO) is quenched and ferromagnetic (FM) transition, which appears at TC=148 K is followed by antiferromagnetic (AFM) transition at TN=104 K. This film shows self-field hysteretic insulator-metal transition (IMT) at TIMC=89 K and TIMW=148 K in the cooling and warming cycle, respectively. Application of magnetic field (H) gradually enhances TIMC and TIMW, reduces the thermoresistive hysteresis and TIM diminishes. In contrast, the film annealed in flowing oxygen shows a CO transition, which is followed by FM and AFM transitions. This film shows appreciably smaller magnetic moment and does not show IMT upto H=20 kOe. As H is increased to H=30 kOe, IMT having strong thermoresistive hysteresis and sharp resistivity jumps appears in the cooling and warming cycles. As H increases to higher values the thermoresistive hysteresis is reduced, resistivity jumps are observed to disappear and TIM decreases. In the lower temperature regime the resistivity first decreases slowly with H and then shows sharp drop. The virgin cycle is not recoverable in subsequent cycles. The decrement far more pronounced in the oxygen annealed film and occurs at much higher H suggesting that the frozen cluster glass state is more robust in this film. The microstructural analysis of the two set of films shows CO quenching, FM transition and self-field IMT in air annealed film is caused by higher density of microstructural disorder and lattice defects. The difference in growth ambience of the two films could give rise to such microstructural perturbations.
Transport in ultrathin films of LaNiO3 evolves from a metallic to a strongly localized character as the films thickness is reduced and the sheet resistance reaches a value close to h/e2, the quantum of resistance in two dimensions. In the intermediate regime, quantum corrections to the Drude low- temperature conductivity are observed; they are accurately described by weak localization theory. Remarkably, the negative magnetoresistance in this regime is isotropic, which points to magnetic scattering associated with the proximity of the system to either a spin glass state or the charge ordered antiferromagnetic state observed in other rare earth nickelates.
Heteroepitaxy offers a new type of control mechanism for the crystal structure, the electronic correlations, and thus the functional properties of transition-metal oxides. Here, we combine electrical transport measurements, high-resolution scanning transmission electron microscopy (STEM), and density functional theory (DFT) to investigate the evolution of the metal-to-insulator transition (MIT) in NdNiO$_3$ films as a function of film thickness and NdGaO$_3$ substrate crystallographic orientation. We find that for two different substrate facets, orthorhombic (101) and (011), modifications of the NiO$_6$ octahedral network are key for tuning the transition temperature $T_{text{MIT}}$ over a wide temperature range. A comparison of films of identical thickness reveals that growth on [101]-oriented substrates generally results in a higher $T_{text{MIT}}$, which can be attributed to an enhanced bond-disproportionation as revealed by the DFT+$U$ calculations, and a tendency of [011]-oriented films to formation of structural defects and stabilization of non-equilibrium phases. Our results provide insights into the structure-property relationship of a correlated electron system and its evolution at microscopic length scales and give new perspectives for the epitaxial control of macroscopic phases in metal-oxide heterostructures.
The nature of the metal insulator transition in thin films and superlattices of LaNiO3 with only few unit cells in thickness remains elusive despite tremendous effort. Quantum confinement and epitaxial strain have been evoked as the mechanisms, although other factors such as growth-induced disorder, cation non-stoichiometry, oxygen vacancies, and substrate-film interface quality may also affect the observable properties in the ultrathin films. Here we report results obtained for near-ideal LaNiO3 films with different thicknesses and terminations grown by atomic layer-by-layer laser molecular beam epitaxy on LaAlO3 substrates. We find that the room-temperature metallic behavior persists until the film thickness is reduced to an unprecedentedly small 1.5 unit cells (NiO2 termination). Electronic structure measurements using x-ray absorption spectroscopy and first-principles calculation suggest that oxygen vacancies existing in the films also contribute to the metal insulator transition.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
