Thermal stability of magnetization in perpendicular thin film media

Abstract

Inbodnetion The anal densim of hard disk drives mav exceed ZOGWid arnirnd the yew 2000. The future nCOrdi i~~iediu i '~ & & d i i G a t h G e F & & g l i y G i G iduoed Ai&c-cryitaliine size and magnetic exchangedecoupled s l ~ ~ c t u r e . However. the decrease in gram size increascs the effect of thermal fluctuation[lJ. Perpendicular recording has a high potential for the application to very high areal density magnetic recording. sin= we can employ a thicker recording layer than with the longitudinal recording. Furthermore, the demagnctlzation working between the adjacent recording bils decreases with increasing !he linear recording density. These baric propcrlico are desirable in keeping the thermal stability of w r d e d information especially at high areal densities. Lo this paper, we report on the lhcnnal decay charactetis!ics of perpendicular media and discuss on their future possibilities. Results and DLsrussion We have developed the COCI-alloy pcrpcndicular media with high squmness (Mr/Mu0.95). moderate coercivities (Hc:2.4kOe) and low noise charactcristico[2.3]. The recording and the signal dccay characteristics are compared with those of CoCr Pl longitudinal media with dfferenl thicknesses(20, 16. Sum). The normalized roll-off curyes %oE that the recording resolution is 2€-30% higher with the perpendicular media(thiclmcss-2Snm). The medium SIN at 300kFCI is in the order: CaCrPt(L,Rnrn) > CoCrTa(P.2Snm) or CoCrPt(L,lbnm) > CoCrPt(L,Xnm) > CoCrPt(P.25nm). Here L and P denote longitudinal and perpendicular, respectively. The recorded signal decay characteristics measured at m m temperature for 40 and 400 kFCI recordings arc wmpared in Fig. 1. At 400 kFCI, the longitudinal media showed more than lO%/l@ s. o l signal dmp when the rewrding layer was thinner than I6nm. On L e conwry. the CoCrh perpendicular medium with the high MrlMs showed little signal &cay for all linear dcnrilies. I t is possible lo suppress he demagnetization of perpendicular recording at low h e a r dcnsilm hy employing the high squareness media[2.4,51. With increasing the linear density. the demagnetization becomes weaker with perpeudicular recording mode and the ourput signals at high density rccordmg (Fig.2) showed almost DO signal decay. We have also to lake mto acwuut of the efTect of almosphenc temperahre on signal deca) characteristic[61. The dccay rate of longitudinal recordmg is reponed to be enhanced at higher temperatures more than that expected from a proportional scaling with tempcrature[7l. Thermal stability is discussed based on the KuV/kT value of magnetic swilchmg unit which can be regarded as a crystalline grain core in low noise medtm[8.9], though a careful attention should be payed in delennming the Ku value for polycrystalline magnetic lhin filmr[lOl. Table I shows the Ku values caperimentally determined using the well defmed smgle crystal magneuc thin filmsll I] . 'Ihe Ku values decrease more than 20% by increasing the tempcrature from 290 to 400K. The decrease in Ku value will funher enhance the signal decay. The temperature effect on the recorded signal of perpendicular recording will also bediscussed.