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Register a new userMonoatomic magnetic interfaces in IrMn/Cr/Co thin films probed by grazing incidence X-ray absorption spectroscopy
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Added by
Narcizo Souza-Neto M
Publication date
2013
fields
Physics
and research's language is
English
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We present depth-resolved experimental results on the atomic and electronic structures of the Co-Cr interface on four IrMn/Cr/Co thin films with variable thickness of the Cr layer. Grazing incidence X-ray absorption near edge structure near the Cr K-edge was used, and an Angstrom resolved depth-profile for this layer was obtained. An interdiffusion between chromium and cobalt layers was observed in all films, being more pronounced for samples with thinner Cr layers, where Cr behaves as an amorphous material. This causes a contraction in coordination distances in Cr near the interface with Co. In this region, a change in the electronic structure of chromiums 3d orbitals is also observed, and it appears that Cr and Co form a covalent bond resulting in a CrCo alloy. Ab initio numerical simulations support such an interpretation of the obtained experimental results.
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Surface magnetic properties of perovskite manganites have been a recurrent topic during last years since they play a major role in the implementation of magnetoelectronic devices. Magneto-optical techniques, such as X-ray magnetic circular dichroism, turn out to be a very efficient tool to study surface magnetism due to their sensitivity to magnetic and chemical variations across the sample depth. Nevertheless, the application of the sum rules for the determination of the spin magnetic moment might lead to uncertainties as large as 40% in case of Mn ions. To overcome this problem we present an alternative approach consisting of using X-ray magnetic circular dichroism in reflection geometry. Fit of the data by using a computer code based in a 4X4 matrix formalism leads to realistic results. In particular, we show that surface and interface roughness are of major relevance for a proper description of the experimental data and a correct interpretation of the results. By using such an approach we demonstrate the presence of a narrow surface region with strongly depressed magnetic properties in La2/3Ca1/3MnO3 thin films.
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We studied the structural and magnetic properties of FeC~thin films deposited by co-sputtering of Fe and C targets in a direct current magnetron sputtering (dcMS) process at a substrate temperature (Ts) of 300, 523 and 773,K. The structure and morphology was measured using x-ray diffraction (XRD), x-ray absorption near edge spectroscopy (XANES) at Fe $L$ and C $K$-edges and atomic/magnetic force microscopy (AFM, MFM), respectively. An ultrathin (3,nm) $^{57}$FeC~layer, placed between relatively thick FeC~layers was used to estimate Fe self-diffusion taking place during growth at different Ts~using depth profiling measurements. Such $^{57}$FeC~layer was also used for $^{57}$Fe conversion electron M{o}ssbauer spectroscopy (CEMS) and nuclear resonance scattering (NRS) measurements, yielding the magnetic structure of this ultrathin layer. We found from XRD measurements that the structure formed at low Ts~(300,K) is analogous to Fe-based amorphous alloy and at high Ts~(773,K), pre-dominantly a tifc~phase has been formed. Interestingly, at an intermediate Ts~(523,K), a clear presence of tefc~(along with tifc~and Fe) can be seen from the NRS spectra. The microstructure obtained from AFM images was found to be in agreement with XRD results. MFM images also agrees well with NRS results as the presence of multi-magnetic components can be clearly seen in the sample grown at Ts~= 523,K. The information about the hybridization between Fe and C, obtained from Fe $L$ and C $K$-edges XANES also supports the results obtained from other measurements. In essence, from this work, experimental realization of tefc~has been demonstrated. It can be anticipated that by further fine-tuning the deposition conditions, even single phase tefc~phase can be realized which hitherto remains an experimental challenge.
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