Zr(Fe1-xMx)y(M = Co, A1) IN THE TRANSITION REGION : SPINGLASS OR LONG RANGE MAGNETIC ORDER ?

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Zr(Fe1-xMx)y(M = Co, A1) IN THE TRANSITION REGION : SPINGLASS OR LONG RANGE

MAGNETIC ORDER ?

G. Wiesinger, R. Grössinger, G. Hilscher, E. Wohlfarth

To cite this version:

G. Wiesinger, R. Grössinger, G. Hilscher, E. Wohlfarth. Zr(Fe1-xMx)y(M = Co, A1) IN THE TRAN-

SITION REGION : SPINGLASS OR LONG RANGE MAGNETIC ORDER ?. Journal de Physique

Colloques, 1980, 41 (C1), pp.C1-209-C1-210. �10.1051/jphyscol:1980165�. �jpa-00219734�

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JOURNAL DE PHYSIQUE Colloque Cl

,

supplbment au n O 1, Tome 41, janvier 1980, page C1-209

Z ~ ( F ~ ~ - & ) ~ ( M = Cot ~ 1 ) I N 7HE TRANSITION REGIDM

:

SPINGLASS OR LONG RANGE MAGNETIC ORDER

?

G. Wiesinqer, R. GrBssinqer, G. Hilscher and E.P. ~ o h l f a r t h ' I n s t i t u t fUr ExperimentaZphysik, T . U. Vienna, Austria

+

on leave from Imperial CoZlege, London, U.K.

.Zr(Fel-xC~x)y (y is usually 2) is a model sub- stance f o r investigating a magnetic phase transition: The system crystallises in the cubic C15 (MgCu2) structure over the whole concentration range and becomes paramagnetic a t T = 4.2 K f o r

~ ~ 0 . 7 6 , whereas the Fe rich cmpounds exhibit f e m a g n e t i s m /1, 2/. In the region 0.5<x ~ 0 . 7 6 the magnetic properties depend strongly on the sample preparation and on stoichimetry.

In Zr(Fel-xAlx)2 the situation is similar: A t T = 4.2 K paramagnetism occurs f o r x>0.54. How- ever, the crystal structure depends on x: C15 f o r 0 <x<0.25, C14 f o r 0.3<x<0.8, C15 f o r 0.85<x<0.95, ZrA12 is again hexagonal (C14).

In the present investigation emphasis was laid on the region, Mere the onset of magnetic ordering occurs: 0 . 5 c x ~ 0 . 7 6 f o r the Co canpounds and 0.3cxq0.56 f o r the Al compounds. For x = 0.5, 0.6 and 0.7 also Co compounds with Z r excess

(y = 1.8) and (Fe, Co) excess (y = 2.03) were prepared. Weight losses a f t e r the melting pro- cedure were 0.1 %. Metallurgical and x-ray exa- mination of the stoichimetric compounds did not reveal the presence of any second phases. Drastic changes in the magnetic properties occur in Zr(Fe, Col2 f o r 0.5< xe0.75 i f the Z r amount is enhanced (y = 1.8 ): 1 ) the anisotropy f i e l d r i s e s approximately by a factor three; 2) while at T = 4.2 K the average hyperfine f i e l d is reduced by-25 % the ordering tempewture determined frcm MWbauer measurements decreases to about 1/3

(fig. 1-3)

.

^Results^frombulk magne t i c and Moss- bauer measurements indicate clearly that the compounds with y = 2 and y = 2.03 order ferrmagneti- cally a t ordering temperatures which coincide with the temperatures where magnetic hyperfine s p l i t t i n g occurs in the Kossbauer spectra.

Off-s toichicmetric compounds ~ r ( F e , CO) .8 show f o r x > 0.5 no magnetic long range order. For the concentration range 0.5c x c 0 . 7 different magnetisation curves were obtained a f t e r cooling the smple with and without the presence of an ex-

ternal f i e l d prior t o the measurement. This re- s u l t together with the appearance of a maximum in the low f i e l d susceptibility indicate a spin freezing and magnetic history effects a s observed in mictmagnetic alloys. Similar results have been obtained by'Muraoka e t al. /I/. But in con- trast to our experivents they claim mictmagnetic behaviour f o r the stoichfometric Zr(Fe, Coj2 ccmpounds, whereas we find f r a bulk magnetic measurements f o r the stoichimetric cmpounds

in the concentration range 0.5 c x c 0.7 long range order, no indication of mic tcmagne t i c behaviour

.

A s d d i t i o n a l p m f Mijssbauer spectra were re- corded on the s t o i c h i m e t r i c samples with x = 0.6 and x = 0.72 in a longitudinal external f i e l d of 5 T a t various temperatures. The shape of the spectra is strongly influenced by the magnetic f i e l d , Mich makes the assunption of micto- magnetism unlikely. Thus we conclude that long range magnetic o d e r is evident f o r s t o i c h i m e t r i c

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1980165

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a - 2 1 0 JOURNAL DE PHYSIQUE

Zr(Fe, C O ) ~ whereas mictcmagnetisn occurs f o r the &at also in Zr(Fe, A 1 ) 2 long range magnetic order off-s toichicme t r i c (Zr excess) canpounds which takes place a t T = 4.2 K f o r ~ ~ 0 . 5 4 .

could be due to a charge transfer f m the additio- n a l Z r atoms. A t the c r i t i c a l concentration the hyperfine f i e l d s f o r ~ r ( F e , A l ) ~ do not jmp as significantly as they do f o r Zr(Fe, C O ) ~ . Approxi- mately in the first 10 % of the magnetically ordered region only very mall hyperfine f i e l d s are observed on only a limited number of iron atoms. Heff increases then more rapidly f o r x x 9.46 which is also evident by the observation of

magnetocrystalline anisotropy in hexagonal Zr(Fe, 0 100 300 T(K)

Al) 2 w i t h this value of x. The ordering tempera- FIG. 2.

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Average hyperfine f i e l d vs. temperahre tures determined frcm bulk magnetic measurements of Zr(Fe. 5Co )

.5 Y generally coincide within a few degrees with the

temperature where magnetic hyperfine s p l i t t i n g occurs in the FTossbauer spectra. This indicates

FIG. 1.

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Magnetisation vs. temperature of Zr(FeS5Co ) f o r different y-values.

.5 Y

FIG. 3.

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Average hyperfine f i e l d vs. temperature of Zr(Fea4Co _{0 6}) _Yf o r different y-values. (@)

...

magnetic s p l i t part of spectra, (0)

. ..

^whole

absorption area.

ACKNOW-

We thank Prof. U. Gonser f o r using the magnetic f i e l d equipment of h i s laboratory.

REFERENCES

/I/ G. Hilscher, H. Kirchmw, Phys. Stat. Sol.(a) 29 (1 975) K 169.

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/2/ Y. Muraoka, M. Shiga, Y; Nakamura, J. Phys. F, in press.