L. E. FERNANDEZ-OUTON¹, G. VALLEJO-FERNANDEZ¹, S. MANZOOR², K. O’GRADY^1,*

Abstract

In the recent past it has become clear that one reason for the lack of understanding of the exchange bias phenomenon is the fact that the antiferromagnet is not stable against thermally activated changes. Therefore extreme care is required when measuring these effects. In this paper possible origins of thermal instabilities will be discussed and data shown from measurements undertaken using carefully defined measurement protocols which enable reproducible and therefore interpretable data to be obtained. One interesting feature of the study of these materials is that the actual state of the antiferromagnet cannot be measured directly and must be inferred from the behaviour of the ferromagnet after careful sequence of field and temperature cycling. We report on a study of the thermal stability of exchange bias systems, IrMn/CoFe and FeMn/NiFe, with different thicknesses and grain sizes. The influence of the grain size has been studied and shows that coercivity and exchange bias have different origins. Training effects studied over a range of temperatures from 4.2K to 400K indicate different contributions to thermal instabilities in the exchange biased system from the magnetic state of the antiferromagnet..

Keywords

Exchange bias, Anisotropy, Training effects, Thermal activation, Grain-size effects.

Submitted at: Jan. 25, 2007
Accepted at: April 15, 2007

Citation

L. E. FERNANDEZ-OUTON, G. VALLEJO-FERNANDEZ, S. MANZOOR, K. O’GRADY, Thermal instability in exchange biased materials, Journal of Optoelectronics and Advanced Materials Vol. 9, Iss. 4, pp. 1127-1132 (2007)

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