Electronic structure and optical band gap of CoFe 2O 4 thin films grown on (001) oriented LaAlO 3 have been investigated. Surprisingly, these films show additional Raman modes at room temperature as compared to a bulk spinel structure. The splitting of Raman modes is explained by considering the short-range ordering of Co and Fe cations in octahedral site of spinel structure. In addition, an expansion of band-gap is observed with the reduction of film thickness, which is explained by the quantum size effect and misfit dislocation. Such results provide interesting insights for the growth of spinel phases. © 2012 American Institute of Physics.

Prahallad Padhan

Department Of Physics

FE CATIONS

OCTAHEDRAL SITES

Quantum size effects

RAMAN MODES

Room temperature

Short range ordering

SPINEL PHASIS

Spinel structure

Electronic structure

OPTICAL BAND GAPS

Thin films

Fulltext

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Applied Physics Letters

A ferromagnetic 120 Å thick La 0.7 Sr 0.3 M n O 3 (LSMO) film grown on (001) Si using the sputtering deposition technique demonstrates a large positive in-plane magnetoresistance (MR) at 10 K, in the field window of ± 0.084 kG to ± 0.405 kG, although the bulk LSMO exhibits negative MR. Around the coercive field (∼ 179 G), the positive MR becomes ∼ 11 %. The positive MR of the LSMO thin film is explained by the charge transfer driven localized strong antiferromagnetic coupling at the Si - LSMO interface, which favors the reduction of the Curie temperature T C of LSMO compared to that of its bulk value. The construction of the interface on the top surface of LSMO with ZnO thin films further reduces T C ∼ 30 K and the positive MR decreases to ∼ 1 % for 45 ° oriented in-plane current with the in-plane field. The coupling through Mn - O - Zn at the LSMO - ZnO interface preserves the charge state, and the weak exchange coupling at the (La / Sr) O - ZnO interface reduces the spin-dependent scattering process under the field and thereby, the negative MR. The reduced T C and in-plane low-field MR at 10 K of a series of Si / LSMO / ZnO are the same irrespective of the ZnO thickness, which confirms their interfacial origin. The presence of interfacial spin disorder at the Si - LSMO interface is further confirmed from the increase in resistance at low temperatures, which is explained by the Kondo like effect and quantum interference effect. Our investigations show that the technologically important interfacial magnetic coupling and magnetoresistance could be achieved and manipulated by the selective interfacial exchange coupling. © 2019 Author(s).

Asymmetric spin dependent scattering at the interfaces of Si / La 0.7 Sr 0.3 M n O 3 / ZnO heterostructures

The design, fabrication, and performance of an apparatus for the deposition of complex oxides with highly uniform thicknesses at controllable deposition rates over large area, even on the native amorphous SiO2 layer of (001) oriented single crystal Si, are described. The apparatus makes use of the lateral port of a spherical chamber. The port is maintained at uniform temperature, and it houses a substrate heater. The deposition process is controlled by varying different parameters such as target-to-substrate distance, sputtering power, sputtering gas atmosphere, substrate temperature, and pulsed plasma growth. The system has been tested by growing a series of La0.7Sr0.3MnO3 thin films on Si. The systematic strain relaxation and thus the tunable magnetic properties along with the presence of high-quality surface morphology of the films indicate that the designed system could be used to fabricate different components of oxide electronics-based devices over larger area. © 2018 Author(s).

Review of Scientific Instruments

Apparatus and method for the growth of epitaxial complex oxides on native amorphous SiO2 surface of (001) oriented single crystal silicon

High sensitivity low field magnetically gated resistive switching in CoFe2O4/La0.66Sr0.34MnO3 heterostructure

Applied Physics A

Optical and electronic properties of NiFe2O4 and CoFe2O4 thin films

Effect of epitaxial strain on the cation distribution in spinel ferrites CoFe2O4 and NiFe2O4: A density functional theory study

Restoration of bulk magnetic properties by strain engineering in epitaxial CoFe2O4 (001) ultrathin films

Physical Review B

MonitoringB-site ordering and strain relaxation in NiFe2O4epitaxial films by polarized Raman spectroscopy

Electronic structure and optical band gap of CoFe 2O 4 thin films

Journal	Applied Physics Letters
ISSN	00036951
Open Access	No