IEEE TRANSACTIONS ON MAGNETICS, VOL. MAG-17, NO. 6 , NOVEMBER 1981 3079

MAGNETIC PHASE DIAGRAM IN Fe, Snlmx AMORPHOUS ALLOYS

D. Teirlinck, M. Piecuch, J. F. Geny , G. flarchal, Ph. rangin and Chr. Janot

prepared by a vapour deposition technique and the i r magnetic properties have been investigated. Corrpeti- t ion of f e r n - and antifemmagnetic interaction re- su l t s in quite a coqlex behaviour : x > 0.45 c o m s - pmds to alloys with a typical femmagnetic order and a t r ans i t i on t o a parmgnet ic s ta te at a Wietempe- rature Tc ; at intemdiate composition (0.40 < x < 0.45) the alloys exhibit a double transition : a f i r s t one a t TM is a spin-glass-like transition and a second one a t Tc > TM is from ferro- to parmgnetism; the al- loys on the tin side (0.25 < x < 0.40) transform direc- t l y from spin-glass t o paramagnetic s ta te at 31 or re- rrain parmgnet ic (x < 0.25) whatever the temperature.

Abstract - Amrphous Fex alloys have been

. INTRODUCTION

Simultaneous presence of different mgnetic irter- actions in an a l loy ( fe rn- and ant i ferrompet ism for

phases such as spin-glass or cluster glass states. instance) my result in the appearance of new mgnetic

ta l l ized materials mde of magnetic impurities i n non- mgnet ic mtr ices , in which the competition cones f r o m the coexistence of two types of rragnetic atoms (Pd Fe k [I] for instance) o r arises via mschanisT(& Fe [21 or &J [3]).

A similar behaviour has been recently observed in mrphous alloys Fex Pd B2-x Si16 [41 , (Ni l , o -x FeX)T9 P13Bg [SI ( i n which Fe is the "mgnetic impur~ty" i n non-magnetic Pdg2Si18 o r Ni79P13B8 mtr ices) and in (Fe, kI-X)75P16Bs A 1 3 [ 6 ] (in which Fe and k are two mgnetic species).

sured i n Fex S ~ I - ~ amorphous alloys which have been pre- In th i s paper are reported mp.etic da ta as ma-

?xed in a rather large coqosit ional range (0.20 < x < 0.75). As the comspor,ding crystallized equi1ibriu.n phases can be f e m m g n e t i c (Fe3Sn) or antiferromgne- t i c (Fe Sn and Fe 3-12) , competing short range interac-

result in disordered mgnetic phases, similar t o t h a t tions are expected in the mrphous mterial and my

previously reported [4] [51 [61.

Such a behaviour has been m s t l y observed in c rys -

EXPERIMENTS AND RESULTS

Amrphous iron-ti? f i m have been ?repaEd by the vapour quenching mthcd [71 181 [91 C l O l . Evapo-

kapton polyimide ribbon cooled t o the 1iquid.nitrogen ra ted t in and iron atoms are deposited on an adhesive

rurperature. Tne m r y h o u s t a t e of the samples is characterized by electron diffraction ard electrical res i s t iv i ty neasulrenmts . Further crystallization is avoided by keeping the alloys in liquid nitrogen.

Fagnetic data have been collected using a Foner mgnetoreter, at temperatures ranging from 2 t o 300 K

table samples have beer. obtained by p i l l ing up the and w i t h an applied rrapetic field up t o 20 kOe. Sui-

evaporated f i lm in rectangular prism shape ( 6 x 1 2 x 0.7 m). In order to account for demgnetization ef- fects, the mgnetization u (9) has been masured for each sample at T = 4 .2 K and H = 1300 Oe, as a function

h u s c r i p t received March 4 , 1981

Laboratoim de Physique du Solide (L. A. 155) C. 0 . no 140 - 54037 - NANCY-CEDEX (France)

'I - x

Fig. 1. C20m-b.y of the mgnetization mgasuremnts.

of the orientation 9 of H with respect. t o t he sample surface (fig. 1). Changes of u ( 0 1 , between 0- a t e i = 90° and or,, at e l = 180°, are shown in E?e figure 2. Tne demagnetizing factors N1 , N2 , N3 have been also detenrined in the directions of the Ox, Gy, Oz axes as sham in the figure 1, using hys-ceresis loop data f r o m strangly mgnetic samples ( usat > 120 m / g

7 0

5 0

3 0

Fig; 2. Dependence on the sample orientation of the mgnetization value.

Fe at 4.2 K which corresponds t o x > 0.45). Indeed, Mdssbauer investigations have previously given ev?:Lden- ces [lo1 of a uniaxial mgnetic anisotropy in these arrorphous alloys, with the easy direction pewndku- lar to the film plane. A multidorrain structu-r my be suggested. Tnen the rraxirmun slope (do/dH),, in the hysteresis loop is given by fqe reciprocal demgr-eti-

t icular orientmior. of the sample. We have reasured : zing factor l/N [111 (f ig . 3) corresponding t o t h e p a r

N1 ( e l ) = 1.5 and N2 ( e 2 ) = 11.7 ; N 3 cannot be experi- m t a l l y obtained due TO geomtrical constri?s of the e x p e r k r t s but has been estirrated. to be about 0.2 tlxough the surface ratio of the sample faces. 'The sm. N 1 + N2 + Ns = 13 . 4 i s -hen not too far from +he 1 2 . 6 theoretical value.

Fig. 3. Determination of the demagnetizing factor using the maximum slope in rhe hysteresis loop.

0018-9464/81/1100-3079S00.75 0 1981 IEEE

3080

The samples being in the 81 orientation experi- m t s have been carried out as the following :

(i) nngnetization c u r ~ s have been recorded f r o m 4.2 t o 300 K with H up t o 20 kCe. These curves exhibit l inear parts between 15 and 20 kOe whose extrapolation to H = 0 gives saturation values us (x) versus composi- t ion (see f ig. 4 corresponding t o us (x) at 4 .2 K and

Fig. 4. Saturation mgnetization data at 4.2 K as a function of the iron concentration.

which is a refinement of preliminay data previously published [81). "High field" susceptibil i t ies are also deduced f r o m the slopes of these linear parts (fig. 5).

with a constart 1CO Oe external f ie ld . After dem- gnetization a-c room temperature the sanples am coo-

applied and u (TI is m a s u e d f r o m 4.2 K t o 250 K led ir zem field <om to 4.2 K, t5en H = 100 Oe is

and from 250 K t o 4.2 K. Three different -d-iemm- gnetic behaviour have been obtained :

iron (x .L 0.45) the sa-ation rragnetization is (a) For alloys relatively r ich in

rather large ( us > 120 em/g Fe) and the high f i e l d suscegtibility is smaller than 3.5 x IO-'+ em/cm3. The t h e m m g n e t i c curve e A i b i t s a smeared mximm ( f ig . 6 ) . Such a behaviour is typical of a f e m m - m e t whose Curietenprature T, can >e ?etermi?ed as shmn in figure 6. lhe comsgonding value u/H (Tc) is not too f a r from Lts theoretical lhit l / N i 1121.

(ii) t h e m m g n e t i c curves have keen recorded

0 TOlJ 5 0 100 150 2G- 250 3x0

Fig. 5. T h e m r a p e t i c curve u(T) obtaimd f r o m a Feo.4sSno,ss mrphous alloy with a 100 Oe ZP- pl ied f ie ld .

(b) In t he i n t emdia t e compositional range (0.40 < x < 0.451, os ranges from 70 to 120 emu/g Fe and the high f ield swceptLbiliq f r o m 3.5 x t o 6.5 x m/cm3. The o(T) curve

r a m (T & 60 K) similar t o t ha t of the prev5ous (f ig . 7) has a reversible evolution at high tempe-

(a) case, and an irreversible trend below Tx (see figure 7) , o(T) remining practically unchanged when T decreases towam& zero.

Fig. 7. Typical t k m m g n e t i c c w v e in the intemedia- te compositional range.

(c) F-er to the t in s ide (0.25 < x c

emu g/Fe with a larger high field susceptibility 0.40) the mgnetization becores poorer ( os < 0.70

(x 6.5 x IO-^ em/cn3). me themrragnetic c1-e exhlbits a single quite sharp -near TH at

nished when returning to 4.2 K ( f ig . 8 . increasing terperature. This rraximum completely va-

4 1 p F G a _____.__

Fig. 8 . Typical t h e m m g n e t i c curve a t lower iron con- centration.

CONCLUSION

loys can be proposed by plott ing the composition de- A magnetic phase diagram of the Fe, s ~ - ~ al-

pendences of Tc (x) and TM (x) as previously deter- mined (f ig . 9). The ferromgnetic behaviour observed

Fig. 9. Magnetic phase diagram of the Fe, S ~ I - ~ mr-

tism ; SG spin-glass state). phous system (P = pararagnetism ; F = ferrumgne-

n i t e c luster of iron atom. In the intermediate com- for x > 0.45 rray result of the existence of an infi-

positional range (0.40 < x < 0.45), the in f in i te ferromagnetic cluster coexists with a number of fi- nite clusters or isolated iron atom which x e an- t i f e m g n e t i c a l l y coupled through Fe-s-Fe bridges. Tnen TM would be a blocking temperature for the fi- nite clusters : i n the T < TM range the alloys have a spin-glass behaviour and the f in i te c lus te r sus- cept ibi l i ty keeps on i n m a s i n g up t o Tc the c r i t i - cal temperature f o r the infinite cluster. Thus i3-1ez-e would be two transitions : one a t TM corresponding to the deblocking of the finite cluster and a second one f m m f e r n t o pararragnetism at T,. With less i ron in the alloys (0.25 < x < 0.40) the mfini te c luster has k e n spread out into smll clusters and the remaining transition is from spin-glass like behaviour t o para- mgnetism at TM.

tion mchanism m n g atoms of the sane chemical specie i n concentrated alloys, due t o the coexistence of di- rect femmgnet ic i s te rac t ions Fe-Fe and indirect an- tifernmagnetic interactions Fe-Sn-Fe which are "ran- domly" nixed in the mrphous state. Magnetization ma- surements up t o 150 k0e will be c h e d out i n a next fu tum to determine the cluster sizes.

Thus we have observed f o r Lhe first tire frustra-

REFERENCES r11 G. J. Niewenhws . B. H. Verbeek and J. A. Kvdosh. _ _

J. Appl. Phys. , 50; 1685 (1979). [21 €3. R. Coles, B . 7 . B. sarkissian and R. H. Taylor,

3081

D l Ph. hgin, M. Piecuch, G. Mal and Chr. Janot,

191 Ph. kgin, G. Marchal, C. burey and Chr. Janot,

[lo] B. Rodmacq';-f(i: Piecuch, Chr. Janot , G. Marchdl and

[I11 D. W. Carnegie Jr, C. m a n c h i t a and H. Claw,

C121 H. Claw, phys. Rev. Lett., 2, 26 (1975).

J. Phys., E, 2085,(1978). Phys. Rev. B 21, 3047 (1980).

ph. Mangin, Phys. Rev. B 21, 1911 (1980).

J. Appl. fiys., so, 7318 (1979).

Philos. &g., 2, 489 (1978). 1, 95 (1969).

131 J. Souletie and R. Tournier, J. Law Temp. Phys.,

L41-G. Dublon, Phys. Status Sol idi (a), 6 0 , 287 (1980). [SI J. brand , Rev. Phys. Appl., 15, 1036 (1980). E61 Y. Yeshurun, M. B. S a l m n , K.V. Rao and H. S.

171 G. M a l , Ph. hgin and Chr. Janot, J. Fbys., men, Phys. Rev. Lett., E, 1366 (1980). C 2 , 91 (1974). -