Exchange Bias, Memory and Freezing Effects in NiFe2O4 Nanoparticles

  • K. Nadeem
  • H. Krenn
Original Paper


Single-phase NiFe2O4 nanoparticles embedded in SiO2 matrix have been synthesized by sol-gel method. Average particle size lies in the range 8–12 nm. Magnetic measurements are taken by SQUID-magnetometer with a maximum applied field of ±7 T and temperature down to 4.2 K. An exchange bias effect in nanoparticles is due to the existence of strong core-shell interactions and it vanishes as the particle size decreases (<4 nm). Spin disorder and frustration appear at the core-shell interface due to broken bonds on the surface. We have observed the exchange bias effect via hysteresis loop shift, when the sample is cooled in an applied field of 5 T. In both AC and DC fields, our system exhibit memory effects at the halted temperatures. Furthermore, a sharp increase of coercivity at low temperatures (<50 K) is observed, which is attributed to increased surface anisotropy at low temperatures. For saturation magnetization vs. temperature data, Bloch’s T 3/2 law (M(T)=M(0)⋅(1−BT b )) is fitted well and yields: B=4×10−05 K−3/2 and b=1.53. All these measurements prove the presence of exchange bias (core-shell interactions), memory effects, validation of Bloch’s T 3/2 law and freezing effects in nickel ferrite nanoparticles dispersed in SiO2 matrix.


Ferrite nanoparticles Core-shell Spin-glass SQUID-magnetometry 


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  1. 1.
    Kodama, R.H., Berkowitz, A.E., McNiff, E.J., Foner, S.: J. Appl. Phys. 81, 5552 (1997) CrossRefADSGoogle Scholar
  2. 2.
    Nadeem, K., Traussnig, T., Letofsky-Papst, I., Krenn, H., Brossmann, U., Würschum, R.: J. Alloys Compd. 493, 385 (2010) CrossRefGoogle Scholar
  3. 3.
    Kodama, R.H., Berkowitz, A.E., McNiff, E.J., Foner, S.: Phys. Rev. Lett. 77, 394 (1996) CrossRefADSGoogle Scholar
  4. 4.
    Martinez, B., Obradors, X., Balcells, Ll., Rouanet, A., Monty, C.: Phys. Rev. Lett. 80, 181 (1998) CrossRefADSGoogle Scholar
  5. 5.
    Kodama, R.H., Makhlouf, S.A., Berkowitz, A.E.: Phys. Rev. Lett. 79, 1393 (1997) CrossRefADSGoogle Scholar
  6. 6.
    Eftaxias, E., Trohidou, K.N.: Phys. Rev. B 71, 134406 (2005) CrossRefADSGoogle Scholar
  7. 7.
    Winkler, E., Zysler, R.D., Vasquez Mansilla, M., Fiorani, D.: Phys. Rev. B 72, 132409 (2005) CrossRefADSGoogle Scholar
  8. 8.
    Jönsson, P., Hansen, M.F., Nordblad, P.: Phys. Rev. B 61, 1261 (2000) CrossRefADSGoogle Scholar
  9. 9.
    Bisht, V., Rajeev, K.P.: J. Phys. Cond. Matter 22, 016003 (2010) CrossRefADSGoogle Scholar
  10. 10.
    Winkler, E., Zysler, R.D., Vasquez Mansilla, M., Fiorani, D., Rinaldi, D., Vasilakaki, M., Trohidou, K.N.: Nanotechnology 19, 185702 (2008) CrossRefADSGoogle Scholar
  11. 11.
    Tackett, R.J., Bhuiya, A.W., Botez, C.E.: Nanotechnology 20, 445705 (2009) CrossRefADSGoogle Scholar
  12. 12.
    Bloch, F.: Z. Phys. 61, 206 (1931) ADSGoogle Scholar

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© Springer Science+Business Media, LLC 2010

Authors and Affiliations

  1. 1.Institute of PhysicsKarl-Franzens University GrazGrazAustria

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