Journal of Magnetism and Magnetic Materials 69 (1987) 199-205 199 North-Holland, Amsterdam MAGNETIC HYPERFINE FIELDS NEAR THE W(ll0)/Fe(ll0)-INTERFACE M. PRZYBYLSKI *, U. GRADMANN and J. KORECKI * * Physikalisches Institut der Technischen Universitiit Clausthal, Fed Rep. Germany Magnetic hyperfine fields near the W(ll0)/Fe(ll0)-interface were analyzed by Monolayer Resolution Conversion Electron M6ssbauer Spectroscopy(MR-CEMS) of 21-layers Fe(ll0) of 21-layers Fe(ll0) films on W(ll0), coated by Ag. Monolayer Probe analysis could not be performed because of enhanced layer-layer-intermixing, caused by misfit dislocation networks. Monolayer Resolution analysis was possible nevertheless because Bht changes strongly from layer to layer. The ground state value is reduced, in the first monolayer, to Bhta(0) ffi 21.4 T, in comparison with 34.0 T in the film center. This agrees with data from diluted W-Fe-alloys. In the second monolayer, an enhancement to BhC2(0)ffi 34.3 is observed, thus clearly establishing spatial oscillation of Bhf(0 ). Temperature dependence of Bhf(T ) can be described by a T 3/2 law. The spin-wave parameter of the W/Fe-interface, like that of the Fe/Ag-interface, is enhanced roughly by a factor 2 in comparison with that of the center. 1.1ntroducfion The unique rank of M~Sssbauer spectroscopy in surface magnetism is given by several advantages: Magnetic hyperfine fields, as indicators of mag- netic order, can be measured, using M~Sssbauer spectroscopy, with high accuracy; in addition, they can now be calculated, in combination with the local magnetization near surfaces and interfaces, using modem methods of band calculation [1,2]; further, it has been shown recently that true monolayer resolution becomes possible near Fe- interfaces using Conversion Electron MiSssbauer Spectroscopy in combination with Monolayer Probes of 57Fe (MP-CEMS). Monolayer probes can be prepared using modem methods of molecu- lar beam epitaxy and can be analyzed using MP- CEMS in situ in UHV (MP-CEMS [3-5]); finally, M~ssbauer spectroscopy, like magnetometric methods, has the advantage of being applicable to interfaces [6], in contrast to spin polarized electron probes of surface magnetism, which are restricted * Permanent address ( * * present address): Solid State Physics Department, Academy of Mining and Metallurgy, Cracow, Poland. to external surfaces and analysis under UHV con- ditions. This seems important with respect to fu- ture applications in ultrathin magnetic film de- vices for ultrahigh density information storage. MP-CEMS has been applied both to the free surface of Fe(ll0) and to Fe(ll0)/Ag interfaces [3,4]. For the case of the free surface, strong inhomogeneities of the magnetic hyperfine field Bhf could be detected, with spatial oscillations as predicted previously [1] for the case of Fe(100). For the case of the Ag-coated surface, no oscilla- tions could be observed in agreement with the general theoretical picture that they are caused by the conduction electrons, which are cut in space for the case of the free surface, but persist at the Ag-coated surface. However, a slightly enhanced hyperfine field was observed, in the ground state, for the first Fe-layer, BhC1 = 34.9 T, to be compared with the bulk value Bht, b = 34.0 T, with monotoneous decrease from Bhf,a to BhCb in a few atomic layers. The aim of the present paper is the extension of this type of analysis to the case of Fe coated by a transition metal, for which strongly changed be- haviour of Bhf near the interface can be expected as a result of interactions between both d-bands. Actually, a strong reduction of Bhf in the surface of polycrystalline Fe-films was observed as a re- 0304-8853/87/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)