Structure and magnetic properties of sputtered Tb/Co multilayers

• Published in: Journal of magnetism and magnetic materials 1992-07, Vol.113 (1), p.227-237
• Main Authors: Ertl, L, Endl, G, Hoffmann, H
• Format: Article
• Language: English
• Subjects: Applied sciences; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Magnetic properties and materials; Magnetic properties of surface, thin films and multilayers; Metals. Metallurgy; Physics
• ISSN: 0304-8853
• DOI: 10.1016/0304-8853(92)91271-T

Multilayers of Tb/Co with equal thicknesses of the single layers ( d Tb = d Co) were prepared on water-cooled quartz and glass substrates by means of a two-source rf-sputtering method. Small-angle X-ray diffraction analysis and transmission electron microscopy on cross-sections of the films revealed a layered structure in all samples with d Tb , d Co ≥ 15 A ̊ . The films with d Tb , d Co ≤ 10 A ̊ behaved as homogeneous TbCo alloys. The existence of compensation points in the temperature dependence of the magnetization of the multilayers indicates a magnetic order in the Tb layers with an antiferromagnetic coupling between the Tb and Co atoms in spite of the fact that pure Tb is paramagnetic at room temperature ( T C = 219.5 K). The extension of the magnetically coupled regions in the Tb layers was calculated from the dependence of the saturation magnetization M S and the compensation temperature T comp on the layer thickness d L of the Tb/Co multilayers. It is about 15 Å at each boundary of the Tb layers and therefore much larger than one would expect from the direct exchange interaction in the ferromagnetic transition metals. The magnetic anisotropy constant K u eff of the films was determined by a torque magnetometer. The linear dependence of K u eff on the inverse layer thickness 1/ d L of the multilayers indicates the existence of a surface anisotropy at the Tb/Co interfaces. The surface anisotropy constant is about K s = 0.46 erg/cm 2.