• PDF / 374,373 Bytes
• 5 Pages / 420.48 x 639 pts Page_size
• 95 Downloads / 243 Views

DOWNLOAD

REPORT

---

STRUCTURAL AND MAGNETIC PROPERTIES OF e--BEAM PREPARED Co.Ptl-x ALLOY FILMS

J.V. HARZER*, B. HILLEBRANDS*, I.S. POGOSOVA*, M. HERRMANN*, G. GUNTHERODT* AND D. WELLER** *2. Physikalisches Institut, Rheinisch-Westf~ilische Technische Hochschule Aachen, Templergraben 55, W-5100 Aachen, Germany. **IBM Almaden Research Center, San Jose, CA 95120, U.S.A.

ABSTRACT We have investigated structural and magnetic properties of CoPt alloy films with strong perpendicular magnetic anisotropy in the thickness range between i00A and 400A. From a detailed x-ray analysis we find highly (111)-textured CoPt microcrystallites in all samples. STM studies reveal a granular topography with grain diameters of up to 250A. Measurements of hysteresis loops yield a saturation field which increases with thickness, and which is consistent with a freely mobile domain model. Brillouin light scattering measurements of the frequencies of the surface and standing spin wave modes yield a bulk exchange constant, which is strongly dependent on the Pt content. INTRODUCTION Polycrystalline Co 1 ,Ptx alloy films have recently been demonstrated as attractive media for magneto-optical storage applications 11-4]. All magnetic parameters are strongly dependent on the film composition, the film thickness and the growth conditions. For alloys evaporated in high-vacuum at ; 200'C a perpendicular easy magnetization axis has been reported in a broad composition range of 50-90 at.% Pt [1]. From the application viewpoint, alloy films have several advantages compared to corresponding Co/Pt multilayers of the same composition ratio. Their fabrication is easier and the Kerr effect is larger, particularly in the UV region, which makes them particularly attractive for future magneto-optical storage applications [2,4]. The microstructure of CoPt alloy films is mainly determined by granular growth and its importance for magnetic properties has been recognized. For instance, Kitada and Shimizu [5] reported for sputtered Co Ptx alloys (x=0-50at.%) a linear correlation between grain sizes and the coercive fieId'strength. The exchange interaction, which is strongly related to the particular microstructure, was identified as one of the most important factors in controlling magnetic properties [6,7]. Murayama et al. [8] measured the exchange interaction in sputtered ColxPtx alloy films (x=0-14at.%) and showed that magnetic inhomogeneities caused by the distribution of grain size and their separation are closely related to the Pt content [8]. For sputtered CoNiPt alloy films the exchange constant was found to be strongly reduced compared to evaporated CoNiPt films [9]. In this paper we present for the first time data on the bulk exchange interaction constant, Aex , for perpendicularly magnetized alloy films investigated by Brillouin light scattering experiments. A structural analysis yields data on the (vertical and lateral) average grain size and the texture of Co 2 5 Pt 75 alloy films. We discuss the thickness dependence of hysteresis properties within the framework of a stripe