PHYSICA Phystca C 235-240 (1994) 2056-2057

North-Holland

Surface barrier effects in non-resonant microwave absorption by superconducting thin films of YBa2CuaOr_a Annt Rastogi a, V.V. Snniv,tsu", M.S. Hegde b and S.V Bhat"

"Depar tmer , t of Physics, lndmn Ins t i tu te of Smm,ce, Banga lore 560 012, India

t'Solid S ta te m,d S t tuc tura l Chemis t ry Unit, Indian l n s t P u t e of Science, BangMore 560 012, htdbt.

We present an unusual tempe~atmxe dependence of h~sterests m the non ~esonant mmrowave ab~mpt~on (NRMA) mgnals trom supmconductmg thin films of YBaaCuaOr- , , We observe thaL the h3stetesis z n c r e u s e s a~th increase m

t, emperatu~e tdl T~ wluch we mtmp~et as evidence fm the plesence of Bem,-L~wngston sulface bamms (BLSB) m the ~mglc clystalhne hhns

i. I N T R O D U C T I O N 3 . R E S U L T S

According to Bean ~tnd Livingston [1], throe emst,~ ,t b , u n e r to the flux peneua tmr , a~,d al.~o to expulsioI, due to the smface x~htch keeps the flUX from pei,etratit~g n, <t supeicoI~ductmg >~tm- ple upto a field Ho lugher than I-]¢]. Konez 3 kowsk~ et a], have reported the eMstence of BLSB ~n single crystal of YBa2(.'u~Or_~ [2]. The3 ob- serve zero magnet~zatiov nt :e~c~se field ~ e e I) ~tnle m fo t~a td ~ c e p flux pene t ra tes at a held t-lp g~eate~ thorn H,: l(ecentl\ Zuo et al [3] haxe tepo, ted the p~e.-ence of >utface b~tniel> In N d~- , ( : e u~ ; (ue O , ,/ \'ke ~epult here the vx,.- tence of BLSB m thin hhns of Yl3aeCuaO,_,, ob- served using the technique of NRMA [4]

2. E X P E R I M E N T A L

Thin superconduc t ing him> el gBa2 ( ' u307 a x~exe deposi ted b\ pul~ed l~tsm abla t ton method [5] on Y-ZrO2 sub>t~au,. 1'he c-axt> ermined hl.ns vr'l'~, - - v:,-,x,.,'R"'W) \k t ' i , t h d i ~ t ( . . . . . ,..t h, , .ul b',, X-l . t '~

ddhact~ot~ alUt four l)~,~be ~e>i~t~xitx ltlt'd'~tll('- llleI ' :Lb

' l he .NttM.\ ~_lg],M>_ ~xete te~mcled u.thg ,t B~ukm 171(2001) X-I).u~d 121'1( .tw(t~on,,t, ,1 cqtupped \~tth <tn ( ) \ to ld ('1"1200 hehunt thin (l\OSttdl The dllOt, tlUlt of tit tllAgllCtlC held ~aa-, pardllcl to the ':-<L\I'.~ ot lht' "~,mplc 'l'he & I~t:t~,It~'tl~ h':'td x~:~- ,x~cl)l ])('IV,('('II -{- ~() ( i \ \ l l ] l l(:

(l 0t}kl D.)m**dul,ttluh

F igure 1 shows the N R M A signals reco,_'ded at v m m u s tempelat tue- . . It is obsmved tha t the zero field h3steresls (dehned as the vmtical separa t io t , be tween for x~ a~ d i t l td 1 evel se sweep sign,d-, a ' zel u field) into eases ~ ith incl ease in temper~u tn e u pro T, while the ~ign,d in tens i ty falls dowr,

A

I/I

c

O

"I- "O I I . "O

R ! ! I -30 0 30

Field (Gauss)

lhgm, ' l \ I~\1 \ "~lgnal5 fol folv.<ud aml lc'X'<.'l.~(' "~vel~> ,~t ~]w held al dlfh'tc'~t tenll)Ct,o m('.~

lIl hgm(' 2 ~<' h,tx~' I)lou('d the ttollll<tllLed h~-,- tme.~l-. (dvlmv, I .~-. tlu, l , t t lo <,~ 7he :c to held I,~-,- I O l e ~ l " , t t ) t ho . . , l~ l l ,~ l i l l l ~ , l l ~ l l \ ) , tg , l l l lml ( ' l" - ' l ) o , ,1,

I l C l l l ~ 14' l l i ]~t ' l , l l i l l , ,)~ , II, ' - . l l l l l ) i ' : . I'll,: ' I1()1 l l l , . I ] [ zcd

h \ > t ( ' t t'..-q.-, t ip I,'+t'.,,,~ q",.lJ~Hl~'llt i,~llx ,t-, ~ , , , t l>pto,ttlt

0921-4534/94/$07 00 © 1994 - Elsevmr Science R V All nghts reserved. SSDI IY)21-4534(94)01594-5

d Rastogt et al/Phystca C 235-240 (1994) 2056-2057 205"

To. The solid l ine in figure 2 is the fit to the equat ion :

Y = 6.1 e x p ( - l . 7 (7~ - T) ° ~') (1)

( / I

B z 0.5 (To_ T)1/2 3.0

Figure 2. F i t of eqn. (1) to the normal ised xeru-

cal hysteresis (see text)

appl ied field and a i tuxon near the ~mlace It varies ~ e x p - ( x / ~ ) , )~ being ~he pen,'tt,ltU,,l d e p t h and x is the d i s tance of th,xon hot, the -,m face. 2) a t t rac t ive in t e rac tmn bet~eetl the [htxolt and ~ts image. It ~anes as e x p - ( 2 l / ~ \ )

For high-T0 su p e rco n d u c to r s the pene t ra t ion d e p t h A c,. (1 - T/Tc) -°~ [6]. The, 'e lore the i,i- t e rac t ions are t e m p e r a t u r e dependent A~ A in- creases with increasing t empera tu re , the mtel- ac t ion also increases leading to an tnciease nl the hysteresis with increas ing t e m p e r a t u r e a.-, ob- served here in the case of thin siugle crystal l ine fihns of YBaeCuaOr-~.

T h e fit of equa t ion (1) to the exl>mituehtal poin ts sho~n in hgure 2 Indicate~ tile c'~'.elfll,tl cor rec tness of this approach .

A C K N O W L E D G E M E N T S T h e au thors v, ould like to thank the (?oum'll ol Scientific and Indus t l i a l l (eseatch and I)epal t- merit of Science and Technolog~ india tot hna . -

clal supl)ol t

4. D I S C U S S I O N

Nmmal ly h3 s tmesis m the NRMA signal> al ~ea due to t r app ing of fluxons. T h e f luxons enter into the sample and get pinned during incle.~suig field Usually a> the tempm~ttme increases the flux(ms get more and mine thermal enetg3. If th> tllel- mal energy is sufficient enough to ovmcome the pruning force, the re is lesa u appiug of fluxons and lesser hysteresis. T ins h.vstmesis due to bulk pru- ning leads to NR~,IA signals for froward and re- verse magne t ic h e l d . weeps at dd te l en t x,due~ of the held (lateral hysteresis). Such h3 stm e>> > ab- sent tit our sample lit the t e m p e r a t u l e tange st tid- ied i l tdlcatmg negligible bulk pinning Instead, a d isplacement of the Mgnals along the x-~t.\l> (xel- ttcal hysteresis) is observed and thin hx sire es,> hi- creases with the ihcl ease m t empe~ at ut e, The ex- planation fol thi~ uitu.',u,d beha~ tout can loe -, ,tl

ht tel I11~ of .-,ut fd.ce I)<u I lel etl('cl '., Bean and [.l\lng>to:l [1] h,~\e .-.uggc>ted that

the Ollglll of >IIch b,tlllel> lies [I1 tv.o I~.llld'~ Ol IIl- t(.'taCttOl:S 1) Iel)U[',t\e ttttel+tCtl<m I)ctx~<'<:tt tlw

R E F E R E N C E S

1 C P Bean and , I D L l \ m ~ < , m Pll~- lh'~ Left 12 (196: ) 1t

2 M l(onez.3kox~skI, l.. lhnl.<hk,_,x ~ '~,'-llll- run :rid 1" l]o}lz{~Ol- }'h\-, 1{~'~ {} 1 { ,1991~

13707 3. F. Zuo S Ktuze toex , Xiugu,mg Iitlng, .I {,

Peng and t t L. Greene , l>h~ ,, l/.¢.~ l,ett 72

(1994) 1746. -1 S V BheLt, P Gangul~, 1'\. I{.,n,aktl.hl.~n

and ( ' N 1~_ Rao a Ph3~ (' 20 (19871 1.55q 5 D ~\1 lIu&ltg, T . Venk~tte.~an ( ' ( ('han,~. I.

Nazm, X I ) \~u A Inanl at .I \[ S Ih%~h' .~ppl Ph3s Lett 5-1 (19q9) 1702

6 E J . Pakuha, R I. S.tn<l._t~,lm 1' ( ' l .~l¢lhlul +trial 11- 13 I,albOX~ ttZ. \l)pI I'll\-, I,oll ~,7 ( lq90) r)t0