Fozia Aziz

Effects of Ti-doping on evolution of coexisting magnetic phases in BaFeO3–δ thin films at room temperature

BaFeO3–δ (BFO) thin films are deposited on different MgO single-crystal substrates with (001), (110), and (111) structural orientations and investigated for the structural and magnetic properties. These films show weak ferromagnetism and magnetocrystalline anisotropy, where (111) axis is found to be hard-axis of magnetization. As Ti-doping should reduce oxygen deficiencies, we have studied the effects of Ti-doping on BFO/MgO (001) system. This doping of nonmagnetic Ti4+ ions (with 3d0 orbital) at Fe-site in BaFeO3−δ largely enhances the magnetization at room temperature. After oxygen annealing of the undoped and doped films deposited on MgO (001), the films show further alteration of magnetization and structure depending on Ti-doping. These films either show a pinched magnetic hysteresis at zero field or a larger coercivity, which was otherwise absent in the untreated thin films. Our results reveal that such changes in magnetic hystereses take place due to the magnetocrystalline anisotropy and/or coexiste...

Contrasting effects of doping on insulating and metallic states of NdNi1−xMnxO3 thin films

We have deposited NdNi1−xMnxO3 (0 ≤ x ≤ 0.10) thin films on SrTiO3 (001), NdGaO3 (001), and YAlO3 (100) substrates and studied the effects of Mn-doping and strain on the charge transport. The majority of charge carriers are holes. Both the in-plane strain and the Mn-doping affect the electrical transport of the films. The metallic state completely vanishes at Mn-doping of x = 0.10. All the films, including x = 0, deposited on SrTiO3 are insulating throughout the temperature range. We find that the resistivity data of all the insulating films fit to two different models, i.e., variable range hopping and Arrhenius equation, in two different temperature regions. The mechanism of charge-transport in the insulating films changes from one type to another and the temperature range of fittings depend on the level of Mn-doping. The results and analyses clearly show that there are contrasting effects of Mn-doping in the metallic and the insulating regions: on one hand, the resistivity increases with increasing Mn-d...

Competing effects of Mn-doping and strain on electrical transport of NdNi1−xMnxO3 (0 ⩽ x ⩽ 0.10) thin films

We have deposited NdNi1−xMnxO3 (0 ≤ x ≤ 0.10) thin films on two different substrates, YAlO3 (1 0 0) and NdGaO3 (0 0 1), respectively, to explore the effects of Mn-doping with compressive and tensile strain. These films show metal–insulator transitions, except for two films with x = 0.10. The Hall coefficient measurements show that the majority of charge carriers are holes in these films. Increasing Mn-doping linearly decreases the temperature coefficient of resistance in the conducting temperature-region. The resistivity increases systematically with increasing Mn-doping in the films with tensile strain, whereas it non-monotonically decreases with doping in thin films with compressive strain. This study reveals competition and combination of different effects of the Mn-doping and of the strain, where the competition and the combination depend on the temperature-region and the type of strain. In addition to the effects of electronic configuration of Mn ions on the free carrier concentration, we find that the effects of Mn-doping on the resistivity are also mediated by the structure, and moulded under the influence of strain. The effects of Mn-doping and strain are distinguished and explained here.

Charge transport in NdNiO3 thin films: Effects of mn-doping versus tensile strain

We have performed a comparative study of total three films, two films of NdNiO3 deposited on SrTiO3 (STO) and NdGaO3 (NGO) single-crystals and one 10% Mn-doped thin film of NdNi0.9Mn0.1O3 deposited on NGO. We find that both, the enhanced tensile strain and the Mn-doping drive the system to an insulating state from a metallic state at high temperatures. NdNiO3/NGO film shows a metal-insulator transition, which disappears in the other two films due to opening of charge-transfer gap. These results reveal that the effect of tensile strain on the resistivity of NdNiO3 is profound at low temperatures, whereas Mn-doping clearly dominates at high temperatures.

Ion-irradiation–induced relaxation of tensile strain and change in directionality of magnetic domains in BaFeO3−δ thin films

Perovskite (BFO) thin films , deposited on MgO (001) single-crystal wafers, were irradiated by ion beams of: i) 200 MeV (Series-1) and ii) 100 MeV (Series-2). These films are investigated for structural, morphological, and magnetic properties. There is a systematic variation in the morphology of the BFO films with increasing beam fluence, resulting in relaxation of tensile strain. The Magnetic Force Microscopy (MFM) images show stripe-like magnetic domains of the remanent magnetization, which were studied by Fast Fourier Transformation. With increasing ion fluence, the formation of stripe domains gradually changes the direction from one crystallographic plane to two planes. MFM patterns of Series-2 show gradually diffusing directionality of magnetic domains with increasing ion fluence. The simultaneous and systematic changes in strain and magnetic properties due to ion irradiation indicate the correlated properties of BFO thin films.

Contrasting effects of compressive and tensile strain and doping-induced opening of charge-transfer gap in NdNi0.90Mn0.10O3 thin films

We have studied the effects of Mn-doping in a series of NdNi1−xMnxO3 (x = 0, 0.10) thin films deposited on NdGaO3 (001) and YAlO3 (100) substrates, respectively with tensile and compressive in-plane strains. Interestingly, only 10% Mn-doping totally suppresses the metallicity in both the thin films indicating an opening of charge-transfer gap. In addition, we have also observed contrasting effects of compressive and tensile strains on electrical transport of Mn-doped thin films. There is an enhancement in magnetization as a result of Mn-doping.

Sharp metamagnetic and correlated electronic transitions in manganites: A systematic effect of cation disorder

We have studied a series of Nd0.5Ca0.5-xBaxMnO3 (x = 0.02, 0.03, 0.05 and 0.10) manganites to explore the effects of A-site cation disorder on antiferromagnetic charge-ordered state at low temperatures. Sharp and multiple metamagnetic transitions are observed in these manganites, which are found to be correlated to sharp resistivity drops at low temperatures. In spite of no significant change in average cation radius at A-site, isovalent substitution of Ba at Casite caused considerably large effects on the charge-ordering and the metamagnetic transitions. Here, we report some systematic trends of features evolving from metamagnetic transitions, as a function of increasing cation disorder.