Role of Coulomb blockade and spin-flip scattering in tunneling magnetoresistance of FeCo-Si-O nanogranular films

Journal Article · Fri Apr 01 00:00:00 EDT 2011 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.3561438· OSTI ID:21538224

Kumar, Hardeep; Ghosh, Santanu ^[1]; Buerger, Danilo; Zhou, Shengqiang; Groetzschel, Rainer; Schmidt, Heidemarie ^[2]; Li, Lin ^[2]; Kabiraj, Debdulal; Avasthi, Devesh Kumar ^[3]

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1. Nanostech Laboratory, Department of Physics, Indian Institute of Technology Delhi, New Delhi 110016 (India)
2. Institute of Ion Beam Physics and Materials Research, Helmholtz-Zentrum Dresden-Rossendorf, P.O. Box 510119, 01314 Dresden (Germany)
3. Inter University Accelerator Centre, Aruna Asaf Ali Marg, New Delhi 110067 (India)

In this work, we report the effect of FeCo atomic fraction (0.33 < x < 0.54) and temperature on the electrical, magnetic, and tunneling magnetoresistance (TMR) properties of FeCo-Si-O granular films prepared by atom beam sputtering technique. Glancing angle x-ray diffraction and TEM studies reveal that films are amorphous in nature. The dipole-dipole interactions (particle-matrix mixing) is evident from zero-field cooled and field-cooled magnetic susceptibility measurements and the presence of oxides (mainly Fe-related) is observed by x-ray photoelectron spectroscopy analysis. The presence of Fe-oxides is responsible for the observed reduction of saturation magnetization and rapid increase in coercivity below 50 K. TMR has been observed in a wide temperature range, and a maximum TMR of -4.25% at 300 K is observed for x = 0.39 at a maximum applied field of 60 kOe. The fast decay of maximum TMR at high temperatures and lower TMR values at 300 K when compared to P{sub FeCo}{sup 2}/(1+P{sub FeCo}{sup 2}), where P{sub FeCo} is the spin polarization of FeCo are in accordance with a theoretical model that includes spin-flip scattering processes. The temperature dependent study of TMR effect reveals a remarkably enhanced TMR at low temperatures. The TMR value varies from -2.1% at 300 K to -14.5% at 5 K for x = 0.54 and a large MR value of -18.5% at 5 K for x = 0.39 is explained on the basis of theoretical models involving Coulomb blockade effects. Qualitatively particle-matrix mixing and the presence of Fe-oxides seems to be the source of spin-flip scattering, responsible for fast decay of TMR at high temperatures. A combination of higher order tunneling (in Coulomb blockade regime) and spin-flip scattering (high temperature regime) explains the temperature dependent TMR of these films.

• OSTI ID: 21538224
• Journal Information: Journal of Applied Physics, Vol. 109, Issue 7; Other Information: DOI: 10.1063/1.3561438; (c) 2011 American Institute of Physics; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
COBALT ALLOYS
ELECTRICAL PROPERTIES
GRANULAR MATERIALS
IRON ALLOYS
MAGNETIC PROPERTIES
MAGNETIC SUSCEPTIBILITY
MAGNETIZATION
MAGNETORESISTANCE
NANOSTRUCTURES
OXYGEN
SILICON
SILICON COMPOUNDS
SPIN ORIENTATION
SPUTTERING
TEMPERATURE DEPENDENCE
THIN FILMS
TRANSMISSION ELECTRON MICROSCOPY
TUNNEL EFFECT
X-RAY DIFFRACTION
X-RAY PHOTOELECTRON SPECTROSCOPY
ALLOYS
COHERENT SCATTERING
DIFFRACTION
ELECTRIC CONDUCTIVITY
ELECTRON MICROSCOPY
ELECTRON SPECTROSCOPY
ELEMENTS
FILMS
MATERIALS
MICROSCOPY
NONMETALS
ORIENTATION
PHOTOELECTRON SPECTROSCOPY
PHYSICAL PROPERTIES
SCATTERING
SEMIMETALS
SPECTROSCOPY
TRANSITION ELEMENT ALLOYS