Search

The magnetic interaction between BiFeO 3 and SrRuO 3 layers in a heterostructure grown on (0 0 1) oriented SrTiO 3 substrate is investigated. A two-step magnetization reversal was observed in M−H hysteresis loop measurement of the heterostructure at 10 K. The first step in the hysteresis loop is associated with the switching of the free SrRuO 3 moments whereas the second step arises from the switching of the pinned moments. The total amount of the pinned SrRuO 3 moment was observed to decrease with increasing thickness of the BiFeO 3 layer. The presence of exchange bias effect in the heterostructure was confirmed by the field cooled M−H measurements where only the second step of hysteresis loop was observed to shift along the field axis. The coercivity of the second step of hysteresis loop decreases with increasing temperature and merges with that of the first step above 100 K which infers the desertion of the pinned magnetic moments. Temperature dependent capacitance measurement shows a kink at the ferromagnetic transition temperature of SrRuO 3 and a pronounced dip was observed in the second derivative of capacitance with respect to temperature, indicating a strong magneto-electric coupling between the two layers.

Epitaxial BiFeO(3)thin films with different thicknesses were grown on SrTiO3(001) substrate. The fllm exhibits a structural transformation from ``R-like'' phase with out-of-plane lattice parameter 4.06 ANGS; to a ``T-like'' phase with out-of-plane lattice parameter 4.65 ANGS; on increasing the thickness from 16 nm to 60 nm. The parasitic gamma Fe(2)O(3)phase was avoided by using slightly higher oxygen pressure during the growth. The ``R-like'' phase is shown to exhibit significant magnetic anisotropy and enhanced saturation magnetization which vanishes with the appearance of the ``T-like'' phase.

Large area MoS2 and WS2 van der Waals epitaxial thin films with control over number of layers including monolayer is grown by pulsed laser deposition utilizing slower growth kinetics. The films grown on c-plane sapphire show stiffening of A(1g) and E-2g(1) phonon modes with decreasing number of layers for both MoS2 and WS2. The observed stiffening translate into the compressive strain of 0.52% & 0.53% with accompanying increase in fundamental direct band gap to 1.74 and 1.68 eV for monolayer MoS2 and WS2, respectively. The strain decays with the number of layers. HRTEM imaging directly reveals the nature of atomic registry of van der Waals layers with the substrate and the associated compressive strain. The results demonstrate a practical route to stabilize and engineer strain for this class of material over large area device fabrication. (C) 2017 Elsevier B.V. All rights reserved.

We have carried out extensive comparative studies of the structural and transport properties of CaRuO$_3$ thin films grown under various oxygen pressure. We find that the preferred orientation and surface roughness of the films are strongly affected by the oxygen partial pressure during growth. This in turn affects the electrical and magnetic properties of the films. Films grown under high oxygen pressure have the least surface roughness and show transport characteristics of a good metal down to the lowest temperature measured. On the other hand, films grown under low oxygen pressures have high degree of surface roughness and show signatures of ferromagnetism. We could verify that the low frequency resistance fluctuations (noise) in these films arise due to thermally activated fluctuations of local defects and that the defect density matches with the level of disorder seen in the films through structural characterizations.