MAGNETIC-PROPERTIES OF TM-ZR MULTILAYERS

A 600 Angstrom film of thulium and Tm-Zr multilayers in which the Tm l ayers are separated by 30 Angstrom non-magnetic Zr layers were evapora ted on superficially oxidized silicon substrates under ultra-vacuum co nditions. The thickness of the Tm layers was varied between 8 and 30 A ngstrom. X-ray diffraction gives evidence for a columnar growth along the c axis of the HCP structure, with in-plane compression of Tm layer s thinner than 20 Angstrom. The magnetic structure of the film is quit e similar to that of bulk Tm. On the contrary, the c-axis modulated an tiferromagnetic phase which takes place in the film at T-N approximate to 54 K is not observed in the multilayers. This phenomenon is prefer entially attributed to an enhancement of the ferromagnetic coupling at the edges of the thulium layers, which favours a structure close to t he squared 3-4 antiphase ferromagnetic arrangement of the magnetic mom ents displayed by the bulk below 30 K. A marked trend to ferromagnetis m is observed as the Tm layers become thinner. Contrary to that observ ed in Dy-Zr and Ho-Zr multilayers, the interface and volume anisotropi es do not compensate each other for 8 Angstrom Tm layers. The c-asis m agnetic anisotropy of Tm is preserved whatever the thickness of the Tm layers. The estimated anisotropies are compared with the results of p oint-charge crystal-field calculations. (C) 1998 Elsevier Science B.V. All rights reserved.