MAGNETIC FIELD DEPENDENCE OF THE 57Fe HYPERFINE INTERACTION IN Y(Fe0.1Co0.9)2 AND (Ho0.1Y0.9) (Fe0.1Co0.9)2

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MAGNETIC FIELD DEPENDENCE OF THE 57Fe

HYPERFINE INTERACTION IN Y(Fe0.1Co0.9)2

AND (Ho0.1Y0.9) (Fe0.1Co0.9)2

R. Haferl, W. Steiner, H. Ortbauer

To cite this version:

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JOURNAL DE PHYSIQUE

Colloque

C1,

supplkment au

n

O 1,

Tome

41,

janvier

1980,

page

C1-195

N4GNETIC FI

EU)

DEPENDENCE OF ME 5 7 ~ e HYPERFI

NE

INTERACTION IN

Y

( ~ e ~ .

l ~ ~ o .

9) 2 AND (HQ,. 1~0.9) ( ~ e ~ . l~oO. 9)

+

R. Hafer1,W. Steiner and H. Ortbauer

Ins t i t u t fUr ~ x p e r i r n e n t a ~ ~ k ~ s i k + , Ins t i t u t fUr Angewrmdte Phy s i k , T . U. Wien.

Starting with YCo2 a c r i t i c a l Fe

and

Ho concentra-

tion

(> 10%) was obtained f o r the appswance of long-range magnetic order /1,2/. MictaMgnetism has

t o

be concluded frdn bulk magnetic and neutron de- polarization measurements for both samples. T h e r e fore Mijssbauer measurements without

and

with applied f i e l d s up

t o

1.72Thave

been

performed i n the temperature range 5 to 300K.

The m a t w e TM (determined by the maxjnnnn i n the ttsnperature dependence of the magnetization

reasurea in 1u.v

fields, i f the sanples are cooled to 4.2 Kwithout an applied f i e l d

s)

and the temperature TA (determined by the vanishing of the magnetic hyperfine s p l i t t i n g ) coincides f o r

Y

(Fee.

lCoo. 9) 2, whereas TM <TA i s obtained for the

Fig.1: Temperature dependence of the magnetization for Y(Fe0.1C~0.9)2 (1) and ( H o ~ . ~ Y ~ . ~ )

(Fee.

1

(2)

.

1 (2) cooled without any field t o 4.2 K (2 K) and measured in 0.056 T (0.17 T)

full symbols, cooled in 0.056T (0.17T) open symbols.

Fig.2: Induced hyperfine field H. versus the H /T A

ratio for Y (Fe 0.1C00.9)2 ( 0 ) and

(Hog. IY0.9)(Fe0. 1C00.9) (+I

-

Ho containing s q l e ( f i g

.

I )

.

For T > T ~ a quadruple s p l i t t i n g of 0.44 mn/s (independent of the measuring I r p e r a t u r e ) is observed for both canpounds, i n good aqrement with the value determined f o r YFe2 above the Curie temperature (TC) /3/. Since a l s o for the line-width a value of 0.24 m/s was obtained, the influence of the varying Fe content on the electrostatic interaction

i n Y (Fe ,Co)

is

n g l i g i b l e

.

For both ccqounds the values of the isamer s h i f t (-0.29mn/s a t 300Krela- t i v e to 5 7 ~ o ~ ) and the quackupole s p l i t t i n g are independent of both the different Fe environments and the Ho content.ReinvestigationofY(Feo

.

_.

9)2

leads to the conclusion t h a t the quadruple s p l i t spectrum exhibiting a r e l a t i v e intensity o f - 10% and a different i s m s h i f t /2/ is due to a small

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C1-196 JOURNAL DE PHYSIQUE

amount of Fe i n t h e windm of the proportional counter.

Taking i n t o account t h a t magnetic and -pole interactions are canparable, t h e e f f e c t i v e hyperfine

*

-

.m

f i e l d Heff = Hi

-

HA (Hi induced f i e l d ) was detemined. Heff is t h e sam f o r both samples

( f i g . 2 ) , indicating t h a t a l l Fe at- possess

a

mg- n e t i c m n t and t h a t the a u n t o f substituted Ho

is only of minor importance f o r t h e value of t h e Fe msnent i n the paramagnetic s t a t e . No d i s t i n c t i o n

f o r Fe atoms with d i f f e r e n t environments and there- f o r e no decision as t o d i f f e r e n t mments f o r Fe was

possible. Due t o the l m r a t i o #/T the saturation hyperfine f i e l d could not be determined.

Magnetically s p l i t spectra exhibiting a large k17per-

f i n e f i e l d distributionarerecordedatT<TA (fig.3). Caused by the Ho substitution the mean hyperfine f i e l d a t 5Kand T A a s well a s TM increase, whereas the magnetization a t 4Kand 6.6Tdecreases (fig.1). It was not possible to analyze these spectra using a b i n d a l d i s t r i b u t i o n taking i n t o account e i t h e r

Fig.3: Temperature dependence of thehyperfine field distribution P (H) for (Ho

0.1'0. 9)(Fe0.1C00. 9) 2 (a) and Y (FeO.lC~O. 9)2 (b). ~ k o k e n line: mean hyperfine field.Ful1 lines: hyperfine field and relative intensities of the subspectra. At 5 Kthe same distribution was measured for different applied fields up to 1.72 T.

only the d i f f e r e n t number of nearest Fe neighbours o r nearest a s well a s next nearest Fe neighbour s h e l l s . A polarization of t h e Co a t m s depending on t h e Fe concentration is indicated by bulk magnetic masurements. In connection with t h e d i f f e r e n t Fe environments these polarized Co atcans may lead to

t h e observed hyperfine f i e l d distribution. For t h e spectrum which exhibits t h e strang increase of t h e quadrupole s p l i t t i n g with decreasing temperature/2/ i n the present analysis a small hyperfine f i e l d is

obtained by taking i n t o account t h a t magnetic and e l e c t r o s t a t i c interactions are canparable. Magneti- c a l l y s p l i t spectra

are

reported f o r 2.2% Fe con-

t e n t /4,5/, which r e f l e c t s the existence of Fe

m-

ments even a t

1m

Fe concentrations.

Frcnn bulk magnetic measurements t h e lack of a TC value, i r r e v e r s i b l e magnetization processes and magnetic history effectsaswellasdisplaced hyste-

resis loops are cbtained. No change of t h e overall shape of t h e spectrum measured

in

1.72 T c a p r e d

to

that measured without an applied f i e l d w a s observed f o r both ccanpounds a t 5K.The r e s u l t s confirm the assumption of spinglass and/or m i c t m g n e t i c beha-

viour

.

/ I / W.Steiner,H.Ortbauer Phys.Stat.So1. (a)

2

(1974) 451,~(1975)KI 19

/2/ H.Ortbauer,W.Steiner,R.Haferl Phys.Stat.So1.

(a)

2

(1977) 157

/3/ M.Morariu,E.Burzo,D.Barb hroc.Int.Conf.Magne-

t i s m (1973) Tcm N, 491

/4/ PI.G.Luijpen,P.C.M.Gubbens,A.M.van der Kraan,

K.H.J.Buschm Physica 86-88 B(19771141 /5/ M.R.Corson,B.Kolk,G.Hoy,G.O.Zimnermann,A.M.

van der Kraan,P.C.M.Gubbens Proc. 4th Int.