Abstract
We estimate the thickness and ordering temperature of an antiferromagnetic and passivation surface oxide through exchange bias coupling. The surface NiO, which is generated through the exposure of a Ni/Cu(001) surface to oxygen, is taken as a model system on which to perform the estimation. Since no exchange bias is found in the surface NiO/Ni/Cu(001), we have built a sandwich structure of NiO/n ML Ni/10 ML Co/Cu(001) to measure the n dependence of exchange bias. With n ⩽ 2, a large exchange bias field is found above 300 K, which could be due to the direct contact between the oxides and the Co layer. With 3 ⩽ n ⩽ 6, a smaller exchange bias field is found with a blocking temperature of 190 K. This implies that the thickness of NiO is, at most, 3 ML. Discovering the thickness and ordering temperature of the surface NiO provides us to explore the potential applications by using surface NiO.
Highlights
The surface oxide generated by the exposure of ferromagnetic (FM) thin films, such as surface Ni oxide (NiO), to oxygen is important because it leads to surface passivation and induces magnetic transitions, such as the spin re-orientation transition (SRT) from in-plane to perpendicular directions at temperatures below 200 K.1–3
The ordering temperature can be obtained by analyzing the exchange bias through introducing an FM layer to generate an FM/AF bi-layer, which results in a shift of the magnetic hysteresis loop and its coercivity (Hc) enhancement)
This could be because the structure of the surface NiO is amorphous or because the surface is covered by oxygen adsorbates that hinder the diffraction
Summary
The surface oxide generated by the exposure of ferromagnetic (FM) thin films, such as surface Ni oxide (NiO), to oxygen is important because it leads to surface passivation and induces magnetic transitions, such as the spin re-orientation transition (SRT) from in-plane to perpendicular directions at temperatures below 200 K.1–3 The surface NiO reduces the critical thickness of the SRT in CoxNi1−x/Cu(001) film systems.[4,5,6] The perpendicular magnetic anisotropy that enhances storage density is important for magnetic storage devices.[7,8,9,10,11,12,13,14,15] characterization of the basic properties, such as the thickness and ordering temperature of the surface NiO, is fundamental in clarifying the mechanism that drives magnetic transitions.[4,5,6]The ordering temperature can be obtained by analyzing the exchange bias through introducing an FM layer to generate an FM/AF bi-layer, which results in a shift of the magnetic hysteresis loop (exchange bias field, Hex) and its coercivity (Hc) enhancement). The surface oxide generated by the exposure of ferromagnetic (FM) thin films, such as surface Ni oxide (NiO), to oxygen is important because it leads to surface passivation and induces magnetic transitions, such as the spin re-orientation transition (SRT) from in-plane to perpendicular directions at temperatures below 200 K.1–3. The surface NiO reduces the critical thickness of the SRT in CoxNi1−x/Cu(001) film systems.[4,5,6] The perpendicular magnetic anisotropy that enhances storage density is important for magnetic storage devices.[7,8,9,10,11,12,13,14,15] characterization of the basic properties, such as the thickness and ordering temperature of the surface NiO, is fundamental in clarifying the mechanism that drives magnetic transitions.[4,5,6]. Resolving the temperature dependence of Hex and Hc allows us to reveal, for example, blocking temperatures (Tb) in the FM/AF system.[16,17,18,19,20]
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