Stabilization of surface spin glass behavior in core/shell-Fe67Co33/CoFe2O4 nanoparticles

ORAL

Abstract

Magnetic properties of Co33Fe67--CoFe2O4 (core-shell) nanoparticles are presented. Both dc magnetization and ac susceptibility measurements indicate a spin glass (SG) like transition occurring at $T$F $\sim $175 K. The SG nature of the transition is also confirmed by the field dependence of the freezing temperature $T$F(H) following the well known Almeida--Thouless line, $\delta T$F$\sim $H$^{2/3}$. Additionally, the particles exhibit a large exchange bias ($H$EB $\sim $ 1357 Oe) arising from the core-shell (ferromagnetic-SG) coupling. The unusually high SG transition temperature and large exchange bias effects are attributed to a combination of several factors including the thickness of the amorphous oxide shell and large values of the exchange and anisotropy constants associated with the CoFe2O4 shell.

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Authors

  • Hassnain Jaffari

    Department of Physics and Astronomy, University of Delaware, Newark DE 19716

  • Syed Ali

    Physikalisches Institut (IIA), RWTH Aachen University, 52056 Aachen, Germany

  • Syed Hasanain

    Department of Physics, Quaid-i-Azam University, Islamabad 45320, Pakistan

  • Gernot G\"untherodt

    Physikalisches Institut (IIA), RWTH Aachen University, 52056 Aachen, Germany

  • S.Ismat Shah

    Department of Physics and Astronomy, University of Delaware, Newark DE 19716, Department of Materials Science and Engineering, University of Delaware, University of Delaware