Direct Measurement of Rotatable and Frozen CoO Spins in Exchange Bias System ofCoO/Fe/Ag(001)

Abstract

The exchange bias of epitaxially grown CoO/Fe/Ag(001) was investigated using Xray Magnetic Circular Dichroism (XMCD) and X-ray Magnetic Linear Dichroism (XMLD) techniques. A direct XMLD measurement on the CoO layer during the Fe magnetization reversal shows that the CoO compensated spins are rotatable at thinner thickness and frozen at larger thickness. By a quantitative determination of the rotatable and frozen CoO spins as a function of the CoO film thickness, we find the remarkable result that the exchange bias is well established before frozen spins are detectable in the CoO film. We further show that the rotatable and frozen CoO spins are uniformly distributed in the CoO film.

Determination of the Fe magnetic anisotropies and the CoO frozen spins in epitaxial CoO/Fe/Ag(001)

“…3 The switching of the 4-fold anisotropy easy axis in AFM/FM system was also reported in other AFM/FM system [44,45,46] and was attributed to the interfacial spin frustration. This result is consistent with our previous result [31]. By comparing the result of Fig.…”

“…Fortunately a systematic temperature dependent study on the anisotropies was already performed on Co/FeF 2 system [34] although XMLD cannot be applied to FeF 2 layer. We also notice an exchange bias field of 300 Oe in the d CoO =4.0nm sample, which is quite similar to the value reported in the literature [31]. The hysteresis loop result suggests that the AFM order of the CoO film after field cooling induces different Fe film magnetic anisotropies at different CoO thicknesses.…”

“…1 shows that the CoO AFM order after field cooling in the Fe[100] direction produces K 4 only in thin CoO thickness regime but all K 1 , K 2 , and K 4 in thick CoO regime. In a previous work, we showed that the CoO spins consists of rotatable and frozen spins with respect to the Fe magnetization rotation, the amount of the frozen spins increases with the CoO thickness, and the exchange bias is not directly correlated to the CoO frozen spins [31]. Then the interesting question is which of the K 1 , K 2 , and K 4 is directly correlated to the CoO frozen spins?…”

“…Although it is expected that the rotatable spins occur at thinner CoO thickness and the frozen spins occur at thicker CoO thickness, it is surprising that neither the exchange bias nor the coercivity of the Fe film follows the amount of frozen spins in the CoO layer [31].…”

Magnetic anisotropy at the buried CoO/Fe interface

“…11 Among O/FM systems, those containing antiferromagnetic (AF) oxides have been the subject of a great number of both experimental and theoretical investigations. [12][13][14][15][16] The preparation conditions, as well as the growth order, are of great importance to understand and control their magnetic properties. 17 In particular, the CoO/Fe(001) interface has been a workbench for many investigations related to AF/FM systems with reactive interfaces, ranging from the exchange bias mechanism, 14,18 to the influence of structure and stoichiometry on the magnetic properties, 19 to the realization of peculiar magnetic configurations, like vortices.…”