Properties and preparation of magnetic materials for bubble domains
- PDF / 2,815,089 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 73 Downloads / 259 Views
d
~
(AK)I/2 M2
w h e r e A is the m a g n e t i c coupling c o n s t a n t , K is the a n i s o t r o p y c o n s t a n t and M is the s a t u r a t i o n m a g n e t i z a tion. Since M and K depend on t e m p e r a t u r e it can be s e e n that for d o m a i n size to r e m a i n c o n s t a n t e i t h e r the t e m p e r a t u r e m u s t be c o n t r o l l e d , or K, and e s p e c i a l l y the s a t u r a t i o n , m u s t be i n d e p e n d e n t of t e m p e r a t u r e near room temperature. IV) The d o m a i n s m u s t be m o b i l e . F o r a given s i z e , m o b i l i t y d e t e r m i n e s the bit r a t e at which a m e m o r y m a y be o p e r a t e d . Although d o m a i n m o b i l i t y can be t r a d e d to some e x t e n t for s m a l l e r d o m a i n s i z e , a goal of a m e g a c y c l e bit r a t e will r e q u i r e a m o b i l i t y of about 100 cm p e r sec oe for a 0.3 m i l d o m a i n V) The m a g n e t i c p r o p e r t i e s of the bubble d o m a i n m a t e r i a l m u s t not be so t e m p e r a t u r e s e n s i t i v e a s to change the size of the d o m a i n s d u r i n g o p e r a t i o n . If d o m a i n size v a r i e s too much the d o m a i n s will not move r e l i a b l y a m o n g the c i r c u i t e l e m e n t s . Given these r e q u i r e m e n t s , the m a g n e t i c m a t e r i a l s now a v a i l a b l e which fulfill them a r e few. The r e q u i r e m e n t s for m a t e r i a l s which a r e t r a n s p a r e n t in thin s e c t i o n s and p o s s e s s a m o m e n t at r o o m t e m p e r a t u r e r e s t r i c t us to the following: I) Hexagonal f e r r i t e s MFe12019; II) F e F s , FeBO3, S p i n e l s MFe204; III) O r t h o f e r r i t e s (R.E.)FeOsi I V ) G a r n e t s (R.E.)sFesO12. The hexagonal f e r r i t e s have been i n v e s t i g a t e d suffic i e n t l y 4'5 to e s t a b l i s h that they have v e r y low d o m a i n m o b i l i t i e s and a r e difficult to p r e p a r e a s l a r g e , high q u a l i t y single c r y s t a l s . F e F s and FeBOs have not yet b e e n p r e p a r e d as l a r g e single c r y s t a l s so t h e i r use in bubble d o m a i n d e v i c e s is s t i l l q u e s t i o n a b l e . 6 S p i n e l s have r e c e i v e d little a t t e n t i o n b e c a u s e they a r e cubic; i . e . , they have no u n i a x i a l m a g n e t i c p r o p e r t i e s . In addition, the p e r f e c t i o n of a v a i l a b l e c r y s t a l s is inadequate.
Orthoferrites The o r t h o f e r r i t e s , which a r e o r t h o r h o m b i c , have r e ceived the m o s t e x t e n s i v e a t t e n t i o n to date, and t h e i r p r o p e r t i e s make them at l e a s t a good t r a i n i n g m e d i u m for bubble d o m a i n work. Since a l l the r a r e e a r t h s , plus y t t r i u m , will f o r m o r t h o f e r r i t e s , it was hoped that f r o m the fifteen o r t h o f e r r i t e s , or the m a n y additional c o m b i n a t i o n s t h e r e o f , an ideal bubble d o m a i n m a t e r i a l m i g h t be found.
Data Loading...
