PHN 9795 1 25--5~1981
~Devic e for prop~gating magnetic dornains".
The invention rela-tes -to a device for propagating
magnetic domains, including a monocrys-talline non-magnetic
substrate bearing a layer of an iron garnet capable of
supporting local enclosed magnetic domains, said layer
having a uniaxial magnetic anisotropy induc~d substantial-
:ly by growth and having been caused to grow epi-taxi.ally
on the non-magnetic substrate, said iron-garnet bei.ng
of -the class o~ iron garnet materials comprising ir,~ the
dodecahedral sites o~ the garnet lattice at least a large
and a small occupant.
I~ magnetic "bubble" domain devices it holds
that the smaller the bubble diameter, tne larger th.e in-
formation storage density which can be achieved. Iron
garnet 'bubble domain materials are pre~erred in bubble do-
main technology because small diameter bubble domains are
stable in these materials. For a bubble domain material
which must be use~ul for -the manu:facture of bubble domain
devices, it is important that the bubbles ~ormed ,in the
material should have a h.igh wall mobility so that compara~
~ tibely small driving :~ields can ca.use rapid bubble movements.
T~lis property permits the use o~ high ~requencies t~ith low
energy dissipQtion,
It :Ls a:Lso lmport;ant that -t;he ma,gnetic bubble
domain mat~:rials shou:l.d have a h.ig:h unia,xial an:isotropy.
This proves to be necessary to avoid spontaneous nucleation
o:f bu'bbles. This is o~ great importance ~or reliab.le in-
f'ormation storage and processing-within the bubble domain
material.
The overall uniaxial anisotropy (Ku) may have con-
tribu-tions o~ stress or strain induced (Ku) and of ,,rowth-
induced (Ku) terms. This rneans tha-t
KU ~ KU -~ Kg ( 1 1
3~
PHN 9795 -2~ 25-~_1981
In the usual bubble domain rnaterials, Ku is rn~Linly
determined by -the grow-th-induced term. In choosing ions -to
occupy dodecahedral sltes in the lattice of' a bu'h'ble garnet
material in order to increase the gro~th-induced anisotropy,
the choice in the past was restricted to magnetic rare ear-th
ions, because -the accepted theory f`or growth~anisotropy
demanded the use of` magnetic ions. However~ the magne-tic
rare earth ions used provide a contrib-ution to the damping,
so that this choice does no-t lead to an op-timum domain
mobility. It is even so that the srnaller the -bu'bble
domain becomes, -the more damping ions ha~e to be incorporat-
ed to reali~e the required high uniaxial anisotropy.
Netherlands Patent ~pplication 7514832 discloses
a bubble domain device in which the bubble domain material
comprises lanthanum and lutetium in dodecahedral sites so as
to ensure the high bubble domain wall mobility which is
desira'ble for operation at high f`requencies of` bu'bble
domairl devices. A f`ilm of this known material proves to have
a growth-induce~ uniaxial anisotropy (Ku) of 6800 erg/cm3,
which is suff`icient to enable s-table device behaviour with
a bubble domain cross-section down to a minimum of 4 /um.
The high growth-induced uniaxial anisotropy
(I~u) of films of this known material is ascri'bed to -the com-
bination of lanthanum (the largest of the rare earth ions)
with lutetium (the srnallest o~ the rare earth ions), while
the high bu'bble domaln wall mo'bili-ty :is a result of the
~act that'both lanthanum and :Lutetium do not contribute
to the ~amping or only contribute to a sma:L:L exten-t. ~Iow-
e~er, a dLsadvanta,~e o~ th:is mater:ia'l :is that lanthanum
can he incorporated in the garnet lattice only to a
res-tricted extent, as a result of which the ef`fect of` the
combination of a large rare earth ion and a small rare
earth ion in the dodecahedral latt:ice sites caNno-t be
-used optically.
It has surprisingly been found that the occupation
of dodecahedral sites by a non-magnetic ion not belonging
to the class of -the rare ear-th ions, namely bismuth, iII
combinatiorl w:ith small rare earth ions, leads to a material
PHN 9795 3~ 2~ 5-'1981
having a comparab:Le mobility to the known rnaterial but
with an approximately l0 x higher uniaxial anisotropy,
so -that it is sui-ta'ble ~or use in bu'bble domain de~ices
having bub'hle domains with a dlameter as small as 0.~ /um.
As small rare earth ions in combinatlon with
bismuth may be utilized lutetium, ytterbium an~ thulium.
Layers o~ iron garnet with a com'bination of
bismu-th ions and small rare earth ions in dodecahec]ral
sites can ~e epitaxially grown on various substrates, in
lD whieh matehing o~ the lattice constant takes place by
a suitable choiee o~ the ratio large ion/small oceupant
in the docLecahedral sites. Grow-th has generally been on
Gd3Ga~01~ (lattice constant aO = 12.38 A.) ,~u-t other
materials which may be utiled are e.g. Eu3Ga5012
(aO - 12.40 ~) Sm3Ga5012 (aO = 12.43 ~) and Nd3Ga5012
(aO = 12.50 ~) or mixed crystals thereof. A face parallel
to -the crystallographic (111) ~ace may serve as a
deposition face.
In those eases in whieh the darnplng o~ the above-
deseribed iron garnet nrlaterial with Bi ions occupyinga part of -the dodecahedral sites is smaller than is in
~act necessary ~'or the applieation in ~iew, on0 has the
liberty o~ subs-tituting, if` desired, damping ions in a
part o~ t'he dodeca'hedral s:ites. If, ~or e;~arnple, Sm or Eu
is used f'or this purpose, the un:Laxial anisotropy constant
may bc ~urther lncreased (by appro~:imately -15%) ~
A pre~erred mater:ial for minirrlizing the growth-
indueed an:Lsotropy is Bi, Y, M ~3 GayFe5_y whereill
is Lu ancL/or Trn and/or Yb. With a fi~ed Ga content in
the layer, the anisotropy constant of layers in which
Lu ~ Tm or Yb) is gradually replaeed entirely by Lu -turned
out to reach a maximum at a Lu : Y weight ratio in ~he
me:it o~ approximately 'I : 1, which corresponds wi-th a
Lu : Y ratio in the iron garnet layer o~ approximately
'I : 2 e:Lements other -than gallium can be substitutecL ~or
iron to reduee the magr1etization o~ the resulting garnet
la~er,and a gerLera:L ~orlmlla ~or ttliS material is
~i, Y, M~3 QyFe5~y0l2, wh~rein Q is a non-rnagnetic ion
g3~
P~IN 9795 ~~~ 2~ 19~1
which preferably occupie.s tetri~hedral lattice sites,
0 ~ y ~ 5, and ~5-~) is suf~iciently large in order tha-t
the material '~e magne-tic at -the operating -tempera-ture~
When a subs~iitution is realized in the iron sites ~ith
an ion having a charg~ of more than ~3, charge compensation
may require that a charge-compensa-ting ion be incorporated
in the dodecahedra~si-tes~ so tha-t a material is provided
o:~` the composition {Bi, Y, M~3_z Jz Qy F~5_yO12,
J is a charge-compensating ion having a charge o~ ~1 or ~2
and which prefera'bly occupies dodecahedral si-tes, Q is a
non-magrletic ion ha~ing a charge of more than ~3, 0 ~ z ~ 3,
and 0 ~ y ~ 5~ In this case also, -the material mus-t be
magnetic at the operating temperatureo~ -the device.
For growth on a rare earth-gallium garnet sub-
.strate, the inventi.on makes i-t possible to choose a nominal
composition of` the bubble domain layer which provides a
minimum deviation ( ~C1.6 x 10 3 nm~ betwe0n the lat-tice
constant o~ the bubble domain layer and the lattice con-
stant of the substrate, as a resul-t o~ which -the stress
or strain in the Pilm is maintained at a su:~ficiently
small value to restrict the possi'bilit~ of cracking and
tearing of the layer. As appears .from the formula which
indica-tes the nominal composition of the present bub'ble
,aomain materials~ there is started from the assumption
that bismu'th~ yttrium, lutetium, thulium and ~tterbium
e~cllls:i~ely substltute in clodecahecL:ral lattice sites. I-t
has 'been ~ound, howe~er, t'hat in the present materials a
small part of the smal.L rare earth ions subst:ihl-tes in
octa'hcdraL 9i~es :i:n t:he :Latt:ice, ~hic:h g:ives :rise to an
imp:ro~ecl temperature dependence of both the satura-tion
magnetisation and the collapse field.
The invention will be described in greater
detai.l~ by way o~ example, with re~erence ~o the ~o].lowing
examp:Les and the drawing.
Figure 1 is a graphic representation of the way
i.n which the ad.apta~on o:f the lattice constant o.~ a
bismuth-containing bu'bble clomain layer to -the la-ttice
constant o:f a GGG-su'bstxa-te (denoted by ~ a) depends on
PHN 9795 -5- 2,~5~'19$1
the weight ratio Y203/Lu203 in the mel-t and on the growth
temperature Tgo
Figure 2 shows dlagrammatically a 'bu'bble domain
device.
Films o~ the nominal composition (Biz~xLu3 x ~)
(Fe5 yGay) 12 were made to grow ~rom a melt by liquid
phase epitax~ techniques while using a PbO/Bi203 flux.
In this case x was varied ~rom 0 to '1.2 and ~ was varied
between 0.-1 and 0.7 on the one hand by varying the ratio
Y203/Lu203 in -the melt and on the other hand by growing
layers at dif~`erent grow-th -ternperatures with a given ratio
Y203/l;u203 in the mel-t. (The lower -tile temperature of the
meltl the more Bi is incorporated in the layer.) ~t is
always possible -to find such combinations of Y203/Lu203
in the melt and growth temperature T that the grown
layers have a lattice constant which di~fers by con-
siderably less than 1.6 x 10 3 ~Lm ~rom the lattice constant
of -the substra-te on which -the layer is grown. A difference
in lattice constant of 1.6 x 10 3 nm has been assumed as
-the limit within which layers o,f good quality can be grown
withou-t cracks or -tearsO All this is explained in t'he
case o:f the use o~ Gd3Ga5012 substrates with refererlee to
Figure 1~ in which the area between the solid lines in-
dicates the conditions in which good layers were de~posited
on the relevant substra-tes without cracks or tears.
The -top line :Lnd:icates ln what c:ircumstances layers were
~ormod w:ith a m:is~:it ~ a o~' approx:i1nately ~'1.6 x '10 3 nm
(these layers were in i;ension),and the bottom line indicat
es in what c:ircu111stances :Layers were formed with a misfit
~ a o~ approximate:Ly -'1.6x'l0 3 nm (-these layers were in
compression).
The layers were rnade to epitaxially grow on sub-
strates immersed horizontally in -the melt at temperatures
'between 680 annd 970C ~or periods varying from 0.5 - 5
35 minu-tes9 the substrates 'being rotated at 100 r.p.m~,the
direction o~ rotation being reversed a~ter every 5
revolut:ions. The layer thicknesses varied f`rom 0.5 to 4 /um.
_
3~
P~IN 9795 -6- 25 ~ 1981
EXAMPLE I.
F~r the growth of a layer having the nominal
composition ~Bi, Lu)3 (Fe, Ga)5O12, the f`ollowing oxides
were weighed out in -the ~ollowing quantities:
Bi2O3133.47 g
P'bO3'19.71 g
LU23 2.35 g
Ga23 4O13 g
Fe23 29.85 g
The mixture was melted and heated to a temperature
of` 723C, A Gd3Ga5O12 substrate having a (11'l) oriented
depos:ition ~ace was dipped in the melt, and a 2 /um thick
layer hacl deposited on it in 3 minutes.
EXAMPLE II.
- For t'he growth of a layer having the nominal
c~omposition (Bi, Y~ Tm)3 (Fe, Ga)5 12~ the following
oxides were weighed out in the followi~g quantities:
Bi23 133.47 g
PbO 319.71 g
Y2O3 1OO35 g
Z 3 5 g
Fe23 29.85 g
Ga23 2.'l3 g
The mixture was melted and hea-ted to a temperature
o~ 855C. A Gd3Ga5Ol2 substrate llavlng a (111) oriented
cleposition ~ace ~as clippecl in the melt, and a 1.'16 /um
thick lLyer had deposited on it in I mimlte.
EXAMPL,E :CIC
For the growth ol` a layer having the nominal
corllposit:ion (Bi~ Y, Lu)3 (Fe~ Ga)5O12~ t~le ~ollo~ing
ox:ides were weighed out in t'he ~ollo~ing quan-tities:
''l33.~7 g
PbO 3'19.71 g
Y2O3 'l.O35 g
Ga2O3 2.13 ~`
Fe23 29.85 g
Lu O l-5 g
PHN 9795 7 2~5-1981
The mix-ture was mel-ted and'heated to a temperature
of 828 C. A Gd3Ga5012 su'bs-trate having a (1'l1) oriented
deposition face was dipped in the melt~ and a layer having
a thickness of 1.96 /um had deposited on it in 1 minute.
EX~MPLE IV
For -the growth o~ a layer having -the nominal
compo5ition (B;, Y, Lu)3 (Fe, Ga)5012, the ~ollo~ lg
oxides we~re weighed out in the following quantities:
Bi23133. 47 g
10 PbO3't9.71 g
Y2031.035 g
LU23 2.00 g
Fe2329.85 g
2 3 3 g
The mi~ture was melted and heated -to a temperature
of 810~C. A Gd3Ga50l2 substrate having a (111) oriented
deposition facewas dipped in the melt, and a layer having
a thickness of 2.38 /um had deposited on it in 45
seconds~
EXAMPLE V
For the growth of a layer having the nomirlal
composition ~Bi~ Y, Lu ~ (Fe~ Ga)5012, the following
oxides were weighed out in -the following quanti-ties:
~i23l33. L~7 g
25 PbO3~9.7l g
Y203'l.635 g
2o31.200 g
2329.85 g
Ga23 1l.5 g
The mixture was melted and heated -to a temperature
of 766 C. An Sm3Ga5012 substrate (lat-tice constan-t
aO = 12.432 ~) ha~ing a ( 111 ) oriented depos,ition ~`ace
was dipped in the melt for 1-1- minu-tes producing a layer
ha~ing a thickness of 3.80 /um.
The said layers hacl the following~ properties:
PHN 979~ -8- 25-~-1981
TABLE
Layer No. i I ~ III . IV ¦ V
~ a (~) ~0.001 _o.007~ 0.00'l-0.002~0.00'l
B(/um) 1.6 1 o.83 2.25 2~63
5 K (erg.cm 3) 3.5~104.36x104 5.2x10 5.4x10 7.9x104
~ H (Oe) j 8 '16 3 1 3 8
4 ~MS(Gauss) 1~ 821 791 1 471 427
(m sec Oe ) ~ l _
__
In the above Table, B is the s-table s-trip domain
width~ .K~ is the uniaxial anisotropy cons-tant, ~ H :is
the ferromagnet:ic resonance line width at 10 GHz, 4~r M
is the satura-tion magnetization and /u is the bubble domain
mobility.
The unia~ial aniso-tropy cons-tan-ts of the resulting
layers were determined by means o.f a torsion magnetome-ter.
Values up to 5.4'x 104 erg/cm3 were thus realized for
(Bi, Y, Lu~3 (~e, Ga)5012 films on GGG, while i-t has been
~ound that these values can be approxima-tely 1.> x as large
20 for the same films on SGG.
Elerewith a ne~ -type o:f bubble domain mater:Lal has
been provided with - also as regards ~ine ~idth and
mo'bility - properties which make it excep-tionally sui.table
for use in bubble domain propagation devices ~ith 1 to 2/um
25 bu'bbl.e domains. 'L`hose ski:Lled in the presellt tecl~lc~)gy
will be capab:l.e o~ varying the composition o~` the bubble
cdoma:ir.~ layer wh:;le using -the gene:ral composition
~B:i~ Y~ M)3_zJz Qy Fe5_yO.!2 withou-t clepart:ing I'rom I;he scope
o:f the p:reserlt :invelltion. Consequent:Ly, the 'E~amples llave
30 'been glven only 'by ~ay Or illustration and are hence not
limiting.
In one embodiment in accordance wi-th the invention,
a substrate 'I and a bu'b'ble domain layer 2 ~or the ac:tive
storage ancl movement of magnetic clomains have a common
35 i.nter~ace 3 9 each bei.ng characterized'by a special. nQ-ture
a:nd 'by an above-clescribed mutua:l. relationship. The ~I.ayer
2 h.as an upper surf'ace 4 rernote :frorn the interface 3, -the
sur:~ace l~ bear:ing certa:in convent:ional elelrlents for the
3~
PHN 9795 9 ~_l981
excita-tion propagation and sensing o~ domains. The l<ayer
2 for the storage or rnovement.o~' magnetic domains,
generally speaking, may 'be the place of any of the va~ious
processes for digital logi.cs, as -these were elaborz.-tely
descri.bed in Patent Specifications and o-ther techni.cal
literature. For exan1ple, reference may be made -ro The
Bell System Technical Journal XLVI, No. 8~ 1901-1925
('19~7) which comprises an article enti-tled "Prope.rties
and Device Applications of Magnetic Domains in Ortho~erri~7
es"~
Figure 2 of the accornpanying drawing shows a
rather simp].e con:E`ig~lration which represents only a.
f`ragment of a normally larger construc-tion comprising
a layer 2 for storage and movement of magnetic domains
and various conventional elements for the excitation7
movement and sensing of magnetic domains. Figure 2 may be
considered to represent a shift register 5 in which.,
according to the invention, a layer 2 of a magnetic material
having a high uniaxial magnetic anisotropy and high domain
7.0 mobility is used~ The easy axis of magneti~a.tion o~ the
layer 2 is perpendicular to the surface 4. The general
magnetiza-tion condition of the layer 2 ls denoted by minus
signs 'lO wh:ich i:ndicate the li:nes of magnetic :E`lux directed
perpendicu:Lar to -the sur:race L~. Magne-tic ~lux lines
s:ituated inside the domains and directed oppositely are
:indicated 'by plus sig:ns~ :E`or exalllplc the plus sign 6
with:Ln condLLcto:r loop 7,
Conductors 'l2, 'l3 and 'I Ll governed 'by a domain
transmltter 9 can be connected to or 'be present in the
irnrnediate pro~irnity of the surface 4 of the layer 2 for
magnetic domains~ in a pre-viously chose:n usual manner.
The conductors 'l2, 'l3 and 'I L~ are coupled respectively to
successive triads of conduc-tive loops, for example, the
loops 8, 8a~ 8b of a ~'irs-t o:E` such a -triad, e-tc. An array
o~ rows and colurnns o~ such multiple l.oop arrangeme:nts
is often used .in storage systems~ A mag:net:ic b:ias fi.eld
~or stabil:i~lng axided domai.ns is provided in a conven-tional
manner, :~or exarllple, by using o:E` a coil or coi:l.s (:not
?~
PHN 9795 -10- ~5~5 l981
shown) surrounding the substrate-bubble domain layer con-
figura-tion, or by the use of permanent magnets
During operation of the device the magne~ic
domains are e~cite~ by means o~ a conventional domain
generator 20 combined with a loop 7 which is sub-
stantial]y coaxial with a loop 8. A stable, cylindrical
domain, ~or example, the position of the dornain indicated
by the plus sign 6, can be propagated in incremental
s-teps from the location of the loop 8 to the location of
the loop 8a, then to that of loop 8b, etc., by successive
excitation of the conductors 12, 13 and 14 etc. by the
domain propagator 9. ~hen a propagated magnetic domain
reaches loop 8n, it can be detected by means of domain
sensor 21. It will be obvious that other digital logic
func-tions can easily be carried out while using the same
~nown methods as those ~lich are used in the example of
the shift register 5.
Flnally, bubble domain layers ~ere deposited from
one melt in a thickness of approximately 1 /um on a ~GG
substrate ~lattice constant a = 12.38 ~) 7 a SGG s~bstrate
(aO ~ 12.43 ~) and a ~GG s-ubstrate (aO = 12.50 ~)0 ~y
varying the growtn temperatures (these were 832 C, 742 C
and 699 C, respec-tively) it wa~ ensured that the lattice
parameter o~ each layer was~dapted as much as possible to
the :Lattice parame-ter of the substrate on which it was
deposited. The rnelt contained 0.9 g of` Y203, l.O g of Lu203
and 2 g of Ga203 a-tld furthtl hacl the salrle compositioll as
that of` example ~. This experirnen-t cdemonstrates that~ by
means o~ the invention, bubble domain layers with very
h:igh uniaxial anisotropy constants (these were 6 x 10
erg~cm 3, 9.l2 x lO erg.crn 3 and 1.1-~ x 105 erg cm~~3
~cspeetively) in combination with high wall mobililies
for which low line widths (these were 4 Oe 7 4 Oe and 1 Oe,
respectively)are characteris-tic , are possible.
