ISSN:
1089-7550
Quelle:
AIP Digital Archive
Thema:
Physik
Notizen:
We have measured the transmission Mossbauer spectra of Fe/Ag(100) single crystal multilayers with large thicknesses (∼100 ML) of intervening Ag as a function of both temperature and magnetic field applied perpendicular to the surface. In contrast to earlier work on samples with less silver between layers, ordering temperatures are much reduced and the initial relaxation effects observed on cooling down appear to set in with a very small or zero order parameter.1,2 Measurements with a magnetic field applied perpendicular to the film surface showed a single well defined order parameter, which rules out superparamagnetizatism as the source of the observed relaxation effects. As an example, a sample measured earlier with 2.4 ML of Fe and 4 ML of Ag exhibited a well defined order parameter in zero field with a transition temperature near 200 K. In the present case a 3.0 ML Fe sample with ∼100 ML of intervening Ag exhibited relaxation effects setting in near 100 K, with a nonzero order parameter below ∼60–70 K. Measurements in a magnetic field showed clear evidence for long range spin–spin correlations even at temperatures above 100 K. Our interpretation is that for the films with relatively thin (∼4 ML) Ag layers between the Fe, there is sufficient coupling between layers to drive an essentially 3-d magnetic transition. With a very thick Ag interlayer separation, the characteristics of the film become much more like an ideal 2-d Heisenberg model, which builds up very long range spin–spin correlations at low temperatures, but whose actual magnetic ordering transition is depressed to T=0 (finite T with anisotropy).3 Presumably the transition which we estimate to be at 60–70 K is driven by the fact that the perpendicular anisotropy is not zero, but in fact is larger than the demagnetizing field.〈ks〉
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1063/1.347833
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