Defects and Magnetic Properties: The Cr/Fe(001) Interfaces
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ABSTRACT We report self-consistent band-structure calculations for the magnetism of Cr overlayers adsorbed on Fe(001) in order to study the role played by imperfect Fe-Cr interfaces, at the microscopic and macroscopic scales, on the total magnetisation. The surprisingly large reduction of the total magnetisation (= - 5 9tB/interfacial atom) recently observed in Cr/Fe(001) through in situ magnetometer measurements is shown to be reproduced only when an interchange of one Cr and Fe monolayer at the interface after deposition of the second Cr monolayer occurs. The magnetic behaviour in artificial structures has been extensively studied both theoretically and experimentally during the last years. One of the most astonishing cases is the FeCr system which has been investigated in overlayer systems as well as in multilayers. The discovery in Fe/Cr multilayers of the giant magneto resistance [1] and the oscillating interlayer coupling [2] effects has stimulated a large number of studies motivated by the desire to progress in the fundamental understanding of the mechanism and by the promising industrial applications like magnetic sensors components. It is now well established [3] that the layered antiferromagnetic (LAF) order, consisting of parallel magnetic planes with antiferromagnetic coupling, in thick Cr layers is stable up to high temperatures (550 K) and is at the origin of the short period in the oscillations of the interlayer couplings [4, 5]. Although the recent experimental results for Cr ultra thin films deposited on a Fe (001) substrate obtained with different techniques [3, 6, 7, 8] are in good qualitative agreement with each other, the magnetic behaviour during the deposition of the first few Cr monolayer on Fe is found to be completely different from that obtained for thicker coverage. Indeed, when the LAF order in Cr is obtained, the magnetisation of the topmost atomic layer changes its sign with the parity of the number of deposited Cr monolayers, but in some cases such a behaviour is not observed for Cr thicknesses smaller than 5 monolayers [6]. Moreover, a change of approximately -5 I.tB/interfacial atom in the total magnetisation has been observed by Turtur and Bayreuther through in situ magnetometer measurements when a few Cr monolayers are deposited on a Fe(001) substrate [7]. This large reduction has been tentatively ascribed to a strong deviation with 247
Mat. Res. Soc. Symp. Proc. Vol. 384 0 1995 Materials Research Society
respect to the LAF order. These authors have suggested that the magnetic moments of the first two Cr monolayers are both opposite to the magnetisation of the Fe(001) substrate, the LAF order being recovered only with the deposition of the third Cr monolayer. Using this hypothetical magnetic moments profile with a Monte Carlo simulation of a non-layer-by-layer growth process, the observed variation of the total magnetisation with the Cr thickness was reproduced [7]. However, the model-profile used by these authors does not result from band-structure calculations. It does not t
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