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MA: Fachverband Magnetismus

MA 19: Poster I (Bio- and Molecular Magnetism/ Magnetic Particles and Clusters/ Micro- and Nanostructured Magnetic Materials/ Magnetic Materials/ Multiferroics/ Magnetic Shape Memory Alloys/ Electron Theory of Magntism/ Spincaloric Transport/ Magnetic Coupling and Exchange Bias/ Magnetization Dynamics/ Micromagnetism and Computational Magnetics)

MA 19.81: Poster

Tuesday, March 15, 2011, 10:45–13:00, P2

Exchange bias due to surface-stabilized spin glass in Co₃₃Fe₆₇-CoFe₂O₄ core-shell nanoparticles — •Syed Rizwan Ali¹, Ghulam Hassnain Jaffari², Syed Khurshid Hasanain³, Gernot Güntherodt¹, and Syed Ismat Shah² — ¹Physikalisches Institut (IIA), RWTH Aachen University, Aachen 52056, Germany — ²Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716, USA — ³Department of Physics, Quaid-i-Azam University, Islamabad 45320, Pakistan

We investigate the magnetic and exchange bias (EB) properties of Co₃₃Fe₆₇CoFe₂O₄ (core-shell) nanoparticles [1]. Both dc magnetization and ac susceptibility measurements indicate the onset of a spin glass (SG) like transition at the freezing temperature of T_F=175 K. The SG transition is also supported by the field dependence of T_F following the well known Almeida-Thouless line, i.e. T_F~H^2/3. Moreover, the particles exhibit a large EB field, H_EB=1357 Oe arising from the core-shell (ferromagnetic-SG) coupling. The unusually high T_F and large EB effects are attributed to several factors including the thickness of the amorphous oxide shell and large values of the exchange and anisotropy constants associated with the CoFe₂O₄ shell.

[1] G. H. Jaffari, S. R. Ali, S. K. Hasanain, G. Güntherodt, and S. I. Shah, J. Appl. Phys. vol. 108, pp. 063921 (2010).