Cr[sub 2]O[sub 3] surface layer and exchange bias in an acicular CrO[sub 2] particle

Zheng, R. K.; Hui Liu; Wang, Y.; Zhang, X.X.
February 2004
Applied Physics Letters;2/2/2004, Vol. 84 Issue 5, p702
Academic Journal
It has been found by electron diffraction and high-resolution transmission electron microscopy that each commercial CrO[sub 2] particle is enclosed by an epitaxial Cr[sub 2]O[sub 3] layer ∼2.5 nm thick. The epitaxial relationships of Cr[sub 2]O[sub 3] layers on CrO[sub 2] particles have been identified. Magnetic hysteresis loops measured at different temperatures (5–300 K), after the sample was cooled from 350 K with a 50 kOe field, were found to be perfectly symmetrical, i.e., no exchange bias was observed, which is unexpected for ferromagnetic/antiferromagnetic core/shell structured particles. To gain a deeper understanding of the phenomenon, the “as-received” commercial CrO[sub 2] particles were annealed at 600 °C in air for 1 h to thicken the Cr[sub 2]O[sub 3] shells. Exchange bias was clearly observed in the annealed particles with thicker Cr[sub 2]O[sub 3] shells. At 5 K, the exchange bias field reached 220 Oe. These experimental observations can be explained well within the framework of the random field model. © 2004 American Institute of Physics.


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