575. 16.0. 10. 760 441 stripes. 910. 1.4. 555. 14.3. 8. 1230. ____. 6. 5. 413. 820. 6.5. 615. 16.4 .... cbservations in the field free state show the magnetic history.
IEEE TRANSACTIONS ON MAGNETICS, VOL. MAG-23, NO. 5 , SEPTEMBER 1987
2055
DOMAIN STUDIES OF C o C r WITH PERPENDICULAR ANISOTROPY J.C.
Lodder, D. Wind, Th.J.A.
Popma, A.
Hubert*
U n i v e r s i t yo fT w e n t e , P . O . Box 2 1 7 , 7500 AE Enschede, The N e t h e r l a n d s . 7 , D-852 E r l a n g e n , FRG. * U n i v e r s i t yo fE r l a n g e n - N a r n b e r g ,M a r t e n s s t r a s s e
Cbtract. R.F. blagnetron sputtered CoCr films (79121 at%) with various thicknesses are magnetically characterized. Thedorcain structure is observed by d i g i t a l l y enhanced Kerr microscopy and &penas on the Hc/Hk values of the samples. For o lw and high axxcivity films a comprison i s made between the measured VSN hysteresis, domain period and a theoretical domain d e l . The b i n shape is a function of the magnetic historyofthe sample and the benaing created by the deposition process.
reversal d e above the critical thickness of magnetron sputtered CoCr layers (5Ld0-808 nm) cl01.Unfortunately(spike-) dorains cannot be r e a l l y v i s u a l i d by neutron depolarization. EXPERIMENTAL PRCCEWRE
The CoCr layers are deposited on Si-substrates by RF mgnetron sputtering, having a 3" target, back pressure1.5~10-7 nbar and P a r = 6x10-3 mbar. The film carpsition is around 21 a t %C r and the thickness (h) i s determined by Magnetic treasurements are carried out by VSM and torque magnetcmeter. i s si (100) single crystal 10x10 mn2. -strate material -ins are observed by a d i g i t a l l y enhanced Kerr microscop. lhelayersare covered with an evaporated 114 ZnS layer. FOughness and beding of the deposited substrate can be nmsured w i t h the Slcan Dektak3030 Stylusinstmnent. Column diamter and lrorpholcgy are determined by STE3 observation using a Jeol 280 cx microsmpe. The relevant sample p r c p r t i e s are given i n Table I.
XRF.
INI'RODUCPION
The reversal mechanism of magnetization i n sputtered CoCr has s t i l l not been layers for perpendicular recording mnpletelyclarified. Studying thedaminconfiguration can contribute t o the solution of t h i s problem. The magnetic properties of C c C r layers are strongly influenced @ variations microstructure, in mrpholcqy and chemical karogeneity. Initial layer effects, C r segregations a t the colunni bwndaries and surface are very important for the final tzhaviour of the danains. The mrpblogy also depends on the sputtering mthcd and parameters used (mainly substrate tanperature and Ar gas pressure). Fran the perpendicular (e.a. hysteresis loop, measured with the VSM, we have i n sane cases, observed a typical shoulder which indicated bubble-stripe dmains.Inorder t o understand m r e a t o u t t h e m i c r a g n e t i c s of such layers one has to correlatethe morphology, rmqnetic prameters and domains. brentz transmission electron lrricrosc~py and d i g i t a l l y enhanced Kerr microscopy have been lsed for damin observations i n CoCr layers. A 1 MeV TIP4 has t o be used for observing Cocr layers thicker than 0.1pm, up t o a m m iu m of 0.3pm [1,2]. A specially designed sample stage to exclude a perpendicularlensfieldfronthe specimen during brain observations is essential [1,31. Different d m i n amfigurations w i t h in-plane magnetization a r e observed i n t h i n ( < 60 nm) CoCr layers C2-41. Tkis can be explained by variations the in preparation methds and consequently differences in mrphology, structure and chemical h q e n e i t y . For a None of the samples used has a well oriented hcpaxis. g x d textured layer (Co77Cr23), having a thickness of50 nm, stripe damins w i t h a width of 0.1pm were observed [21. A maze CfiMin pattern, Iupm fran bubble-like materials, is observed i n films of 8.1 pm thickness having a caoposition of Co82Cr18 [51.Very thin layers (30 mn) w i t h in-plane magnetization show theso-calledripplestructureinCF9Crll C41 and Co79Cr21 C5l. Differentdamin formswere observed i n films w i t h much batter orientation and increased thickness ( > 0 . l p m ) C2-51. A magnetic black-and-white dot structure with a distance between the dots of the same order a s the colunmar diameter has been shown byC31. In this case the film mrphology (one column mnsists of s e v e r a l c r y s t a l l i t e s ) i s t o t a l l y d i f f e r e n t fmthe m a x e d C r y s t a l structure present in [2] which shws a s t r i p e chnain width i n the order of the crystal size. CoCr films i n the range between 17-30 at%C r w i t h a C r segregation i n t o t h e Co~uItmboundaries shOd dot-like Lorentz h g e s which have the Same Sizeas the c o l m diameter [SI. Stripe d m i n widths ( < 0.1 pm) having the s a m size as the colm-diameter are a l s o abserved i n [I]. I t w a s a l s o shcwn t h a t frcsn relatively thick films (0.3 prd, which are mre realistic for remrding applications,the d m i n width i s the satre as the calm s i z e [21 and it i s suggested that the d m i n structure consists of a chain of crystals. Based on neutron depolarization experiments and M.O. t o e a s u r m t s of the surface of our C& films it can ke concluded that thedamin width i s proportional to hX, there x is atout 0.8 for RF magnetron sputteredfilms C6-101. This value i s closer t ot h ec a l c u l a t e d m e r of 2/3 for a branched domain structure [ill than 112 predicted for the Kittel configuration [l2]. I t can also be concluded t h a t reversed spike damins can e x i s t and w i l l influence the
x
1
T a b l e 1: P r o p e r t i e s of the CoCr samples.
Sample
M s kA/m
1 2
410
3 4 5 6 7
423 415 413
8
h
nm
Hc
Kl
kA/m
J/m3*l&
520 4028 13.2 1230 8 14.3 10 16.0 760 441 14.8 18 700 15.5 1300 24 46 1220 16.0 60 700 434 18.4 40 1436 426 16.4 M.O.
Hk
kA/m
Hcjm Pmr d m i n nm
%
shape
525 1.5 660 lo? 555 1.4 910 stripes 575 1.7 790 555 3.2 730 short 4.0 960 stripes 5 9 5 ___ 850 6 1 F 7.5 dot675 8.9 840 like 615 6.5 820
-
KERR OBSERVATIONS
The f i r s t Kerr observations on CoCr layerswithdivergent prqrties are published i n C131. There a specially designed w i t h an irrage processing digitally enhanced Kerrmicrosmpe system is used. The films used have a c a p s i t i o n f r m 17 to 21 a t %C r , thicknesses f r m 96-622 nm and coercivities from 1060 kAjm with one sample of 90 kA/m. They a l l s W a m r e o r less s t r i p e - d m i ns t r u c t u r ea t rsmnence. It was concluded from this that a l l samples reversed by d m i n - w a l l m v m t a s a continuous medium. Using the s a m microscope mentioned above, w caw t ot h e conclusion with our preliminary r e s u l t s C141 that we have t od i v i d e our W r layersinto 3 categories lw H c (longstripe), medium H c w i t h short s t r i p e s mely: o coercivity films w i t h a dot-like (20
