Perpendicular Magnetic Amsotropy in Ultrathin Fe(110) Films on Cr(110)
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PERPENDICULAR MAGNETIC ANISOTROPY IN ULTRATHIN Fe(ll0) FILMS ON Cr(110)
HELMUT FRITZSCHE AND ULRICH GRADMANN Physikalisches Institut, Technische Universiltt Clausthal, D 3392 Clausthal-Zellerfeld, Germany.
ABSTRACT In contrast to Fe(1 10)-films on W(I 10), which are magnetized always in the plane as a result of easy-plane magnetic surface anisotropies (MSA), Fe( 1I0)-films on Cr(1 10) show perpendicular magnetization up to a thickness of roughly 3 monolayers, as a result of a perpendicular MSA of the Fe(ll0)/Cr/(l10) interface. Acoordingly, Fe(l10)-films on W(I10), covered with Cr(110), show asymmetric MSA, the easy-plane MSA of the W(I 10)/Fe(1 10)-interface opposing the perpendicular one of the Fe(1 10)/Cr( 110)-interface. It turns out that MSA is asymmetric too in Fe(1 10) films on W(l 10) covered by Cu, Ag, Au or UHV.
INTRODUCTION Extended experimental work on (out-of-plane) magnetic surface anisotropy (MSA) of bcc a-Fe [1-61 shows perpendicular MSA for Fe(100)-interfaces with Ag, Au and UHV I151, but easy-plane MSA in Fe(lI0)-films on W(1l0), covered with Ag, Au, Cu and UHV 161. Surprisingly, despite of the extraordinary interest in the Fe/Cr-system in connexion with indirect coupling phenomena observed in it 17-111, experimental work on MSA of Fe/Cr-interfaces is missing. The present work will close part of this gap. Following the examples given above, one might guess that the sign of MSA is determined by the ferromagnetic film itself (its material and its orientation) and is independent on the nonmagnetic substrate or coverage material. An inspection of Ni( 111), which shows always easy plane MSA for Cu, Ag, Pd and UHV coverages 1121, and of Co(1 11), which shows always perpendicular MSA 113-151 for interfaces with Ag, Au, Cu, Ir, Mo, Pd and Pt, apparently confirms this rule that the sign of MSA is independent on the contact material (for a general review of ultrathin magnetic films and MSA in them see 1161). We were surprised to find that this rule is broken by Fe(1 10) on Cr(1 10), which shows perpendicular MSA in contrast to the easy-plane MSA of Fe(l 10) on W(l 10). Even more, MSA is of perpendicular type for all known interfaces of Fe(l 10), with the only exception of the Fe(l10)/W(l10)-interface, which shows easy-plane MSA with an exceedingly large magnitude of 1.7 mJ/m 2 which dominates in all films prepared on W(1 10) and makes them easy plane. All Fe(110)-films on W(110) therefore show an asymmetric MSA, perpendicular in one interface and easy plane in the other one, a phenomenon which has not been reported before.
Mat. Res. Soc. Symp. Proc. Vol. 313. c 1993 Materials Research Society
672
PREPARATION Experiments were done using sandwiches of type W(l10)/Fe(1l0)/X and W(ll0)/Cr(110)/Fe(II0)/X, X representing a final Cr-coverage or UHV. The films were prepared in UHV by evaporation (p < 10-10 Torr) onto atomically smooth and clean W(l10)-surfaces, with growth rates of the order of 0.5 ML/min, at substrate temperatures of 300 K, except for Cr base layers, which were prepared with temperatures ra
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