A STUDY ON THE PREPARATION OF LOW RATE EVAPORATED CoCr PERPENDICULAR MAGNETIZATION FILM

Abstract

Serious selective evaporation exists for CoCr films during low rate electron beam evaporation (LREBE), and causes composition discrepancies so that the ratio of x(Crwt%) of the film to X( C1.'I'1t%) of the ingot lies within a ra..'1ge 2.0-3.0. Relations of x with other experiment's factors are given. The reasons for the selective evaporation and composition discrepancies are discussed. On the bases of measured results and micrographs, comparison between the microstructures and magnetic properties of good and poor samples is made. It can be concluded, that many factors influence x and the microstructure of the film and thus also the magnetic properties of the film. Therefore, it is more complicated to control x and the microstructure than in the high rate case. However, the basic theories are similar, and it is useful for studying the basic aspects of CoCr films. In our case, good perpendicular magnetization film (PNF) "\vith I,Is better than 360 (emu/cc) , perpendicular coercivity Hep better than 600(Oe), 4&(50) arround 10(deg) can be obtained. Selective evaporation may exist during deposition, but in papers on high rate electron beam evaporation (HREBE) (1000A~s, beam power 16K'll), where very good CoCr PMFs have been reported[l), we have not seen any mention of this problem. However, if these conditions are not avaible, as in our experiments ,dth LREBE (less than 60Acrs and O.5K1'l) ,and which suffer from other crucial conditions, eg., background pressure pbg of 10E-6 to,rr; no cooling for the substrates ; a distance between ingot and substrate less than 15cm; etc., ca.'} GoCr PNF be acheived? Though the deposition rate compare to that of HREBE is low, it is still usable and is comparable with that of sputtering, but is it still can be used for studying the basic aspects of the CoCr PI·;]'? ;,'hat problems will happen during the deposition?Study of these aspects will have practical significance for the extension of perpendicular magnetic recording applications. EXPERIMENTALThe CoCr PI,IF deposition is made by a home made GlJ;!-450 EB evaporator, with pbg of (2-4)x10E-6 torr, onto glass substrates vTithout cooling. For the deposition rate Rd not to be too low, the distance between the substrates and source had to be ''1i thin 15cm. Halogen lamps were arranged for heating the substrates to desired temperature. The relative substrate temperature Ts which was monitored by a thermocouple is lower than the real substrate temperature.The CoCr percentage "\'las measured by W 5550 :ESl-IA. Film magnetization loops "\'Tere measured by LDJ'9500 ViSN. Torque curves were measured by TP.T-2 'm. Replica micrographs were made by JEM200cx Ta". XDA and Ae(50) .Tere measured by D/max-RB XDA. Film thicknesses t were measured by o(-step200.Through these measurements, it was found that selective evaporation seriously existed during LREBE, and there are many factors ,.;hich can influence the x( Crwt';:) ,deposi tion rate Rd and the microstructure of the films,eg., X(Crwt%) of the ingot and its homogenei ty,the evaporating ti...