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Dependence of exchange bias field and coercivity on spacer layer thickness in FeMn/NiFe/Cu/NiFe spin valve structures

B. PARVATHEESWARA RAO1,2, S. ANANDA KUMAR3, O. F. CALTUN4, CHEOLGI KIM3,*

Affiliation

  1. Research Center for Advanced Magnetic Materials, Chungnam National University, Daejeon, Korea
  2. Department of Physics, Andhra University, Visakhapatnam, India 530003
  3. Department of Materials Science and Engineering, Chungnam National University, 220 Gung-Dong, Yu-Seong Gu, Daejeon, 305-764, South Korea
  4. Faculty of Physics, A.I. Cuza University, Iasi, 700506 Romania

Abstract

Magnetization reversal mechanisms in sputter deposited Cu(5)/NiFe(7)/CoFe(0.3)/ Cu(t)/CoFe(0.3)/NiFe(6)/Fe(20)/ Cu(2) spin valve systems on silicon substrates for different values of t in between 2.0 and 3.0 nm have been studied using vibration sample magnetometry (VSM) and magneto optic Kerr effect spectrometry (MOKE) in surface (longitudinal) and transverse geometries. The exchange bias field matches in magnitude in both the experiments and shows an oscillatory behaviour of interlayer coupling with alternative ferromagnetic and antiferromagnetic alignments, while displaying the highest Hex value for Cu thickness of 2.2 nm in the investigated thickness range. The coercivity also follows an oscillatory trend with enhanced values for successive Cu thicknesses. However, the coercivity values obtained by MOKE are found to be larger compared to VSM, which is attributed to the presence of highly polarized CoFe protective layer in either side of the Cu spacer. The variations in exchange bias fields are discussed in terms of the confinement of quantum well states at the two interfaces of the Cu spacer layer..

Keywords

Exchange coupling, Coercivity, MOKE study, Spin valves.

Submitted at: April 1, 2008
Accepted at: July 1, 2008

Citation

B. PARVATHEESWARA RAO, S. ANANDA KUMAR, O. F. CALTUN, CHEOLGI KIM, Dependence of exchange bias field and coercivity on spacer layer thickness in FeMn/NiFe/Cu/NiFe spin valve structures, Journal of Optoelectronics and Advanced Materials Vol. 10, Iss. 7, pp. 1881-1884 (2008)