Tendency of preferential occupation of transition elements on crystalline sites in rare earth - transition based compounds

Tendency of preferential occupation of transition elements on crystalline sites in rare earth - transition based compounds

~ Solid State Communications, Vol. 85, No. 3, pp. 185-188, 1993. Printed in Great Britain. 0038-1098/9356.00+.00 Pergamon Press Ltd Tendency of Pre...

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Solid State Communications, Vol. 85, No. 3, pp. 185-188, 1993. Printed in Great Britain.

0038-1098/9356.00+.00 Pergamon Press Ltd

Tendency of Preferential Occupation of Transition Elements on Crystalline Sites in Rare Earth - Transition Based Compounds Jifan Hu* and Zhenxi Wang Institute of Physics, Academia Sinica, Beijing 100080, P.R. China *Present Address: Max-Planck-Institut fur Metallforschung, Institut fur Physik, Heisenbergstrasse 1, 7000 Stuttgart 80, Germany.

(Received 20 Ju/y 1992, acceptedfor publication 23 October 1992 by D. Van Dyck) In this work, the crystalline environment of DvTiFel~_xCox is studied by S~Fe Mossbaner spectroscopy. Results indicate that Co prefers to occupy 8f site and Ti prefers 8i site. For rare earth- transition based compounds, we suggest one experimental rule which gives a general description on the tendency of the preferential occupation of the transition elements on transition type crystalline sites in such compounds: Transition atom with smaller atomic number or with smaller number of d electrons has a preferential tendency to occupy the site with larger transition-transition distance; meanwhile the transition atom with the large atomic number prefers to occupy the transition sites with relative short tr~sition-transition distance. Besides it seems that we can treat A1 like a quisitransition atom with the atomic number smaller than that of Cr when A1 participates in substitution in rare earth - transition based compounds.

Rare earth- transition based compounds are of great

Fel_=Oox)il compounds by SZFe Mossbaner spectros-

significance in both science and technology. Two phases

copy. The results indicate Co prefers to occupy 8f site[5].

SmCos, Nd2Fei4B among those compounds have ab-

In this work we report the crystalline behavior for the

sorbed great attention due to their good hardmagnetic

heavy rare earth compound D~/TiFe11_=Coxby study-

properties.

ing 5TFe Mossbaner spectroscopy.

SlnU05 is of U,zC~s hexagonal structure [1] with the

Meanwhile based on analysis of the experimental data

space group P6/mmm, where rare earth atom is on la

on crystal structure for rare earth - transition based

s i t e , transition elements are on 2c and 3g sites.

compounds, we suggest a rule which gives a general de-

Nd2Fe14B is of tetragonal structure with the space

scription on the tendency of the preferential occupation

group P4z/mnm, where Nd occupies 4f and 4g sites; the

of the transition elements on transition type crystalline

transition elements occupy 4c, 4e, 8jl, 8j2, 16ki and

site in such compounds. The DyTiFell_,~Co= (x=0,1 and 3) compounds were

16h2 six sites[2].

prepared by melting the elements of purity 99.5 w~,or

Recently one novel Fe-rich compounds R-FeI2_zM~ have been found to be of ThMn12 body-centered tetragonal

better under argon atmosphere. The button ingots were

•structure with space group I4/mmm, where R occupies

melted four times to ensure homogeneity, then sealed in

2a site ; the transition dements occupy 8i, 8j and 8f

a quartz tube and annealed at 900 ~C in vacuum for one

three sites[3,4].

week. X-ray diffraction (Co-Ks radition) pattern indi-

In previous paper we studied the hyperflne interaction

cated that the compounds were almost single phase with

and crystalline environment in light rare earth NdTi(

ThMn12 -tetragonal structure. The Mossbauer spectra 185

186

Vol.85,No.3

CRYSTALLINE SITES IN RARE EARTH

x=O ......

8f 8f

. . . . . . .

.

.

.

.

.

8i

1.00

•..

3i

8J8i

, ~.,

.__~".':...',.

%

',

~. z

."'.I!!",

.

Y~ --

m

,

!i \]

tl"

.

o 8i

.. t,'.

o

z

¢0 o

~

.i

L:

0.96 1

• °°~o 1.00

.

Velocity (mm/s'8f~ x=1 , , , . , , ...... 8f . . . . . . 8j . . . . . . 8] ' . . . . . 8i ......

' ' ' ' [ 1

1112

1 1 1 1 3

X

Fig.2: The number of iron atom occupation N at different iron site 8i, 8j and 8f in

DyTiFeu_=Co=.

f

\,J,/it

.>

v Y\.,'.

for each iron site 8i,8j and 8f is shown in fig.2.

"~m 0.98[

DyTiFe11, the

iron occupation on each site

For

nsi:nsFnsf

= 3:4:4. That is to say the Ti atom prefers to occupy

Velocity (,mm/s! 8f ...... 8f . . . . . . ,

x=3

8j ,8j '8i

With increasing of cobalt content in compounds,for DyTiFe8Co3,

nsi:nsj:ns/ =

3:3.4:1.6. The number of iron

occupation N for 8f site decreases sharply. The cobalt

co°°" 1.00l .>

the 8i site which has the largest average Fe-Fe distance.

?! ,~!

atom prefers to occupy 8f site which has shortest Fe-Fe

:~ ~/- ~.~

distance among three iron site. As a result, the Curie

0.9[

temperature increases rapidly with the initial replace-

-10-8-6-4-2

0 2 4 6 8 1() Velocity (mm/s)

ment of iron atom on 8f site by cobalt. If we look into the case in

Nd2(Fel_=Co=)14B,we find

a very similar thing that cobalt prefers to occupy 16k2 Fig.l: The Mossbaner spectra of DyTiFe11-=Co=with

site which has the smallest Fe-Fe distance among six unequivalent sites. Is there a rule in the preferential oc-

x = 0 , 1 and 3.

cupation of cobalt in R-Fe based systems? It is our first question. Another interesting thing is that iron prefers were measured using a constant acceleration spectrome-

to occupy 8j2 site[6] which has the largest average Fe-

ter with a 50mCi source of aTCo in palladium at room

Nd2(Fe,Co)14B. Since the preferential occupation of Ti in RTi(Fel_=Co=)His somewhat similar to the case of Fe in Nd2(Fel-=Co=)z4B, we may ask

temperature. The velocity scale was calibrated using an a-Fe absorber at room temperature. The Mossbaner spectra of DyTiFe11_=Co=with x=0,1

Fe distance in

whether there exists a physical connection between two

and 3 measured at room temperature are shown in Fig.1.

cases of Ti and F e or not.

A least-squares method was used for computer fitting of

Indeed above two question are somewhat strange, per-

DyTiFe11_=Co= compounds.

It is our second question.

The

haps one may answer t h e m simply as that it is due to

site assignment were performed similar to the previous

the minimum of total free energy. However it were these

the spectra for the

work[5]. The continuous curve through the data points

two questions which induced us to analyse the tendency

represents a fit to the spectrum.

of preferential occupation of transition elements in other

The composition dependence of the iron occupation

R-transition based compounds such as some CaCu5 type

Vol. 85, No. 3

CRYSTALLINE SITES IN RARE EARTH

187

compounds. We chose this system because there already

when A1 participates in substitution in rare earth - tran-

exist a lot of useful neutron diffraction data in recent

sition (R-T) based compounds.

past twenty years, which help us to answer above two

Moreover we want to point out that even though we

Th(UoxFel-x)S

here found a rule to describe the tendency of preferential

was investigated by means of neutron diffraction by Ele-

occupation for transition element in R-T based com-

mans and Buschow in 197417]. they found that Fe is

pounds, we don't know yet why atoms have such be-

preferentially located on the 3g site (1/2,0,1/2) and Co

havior. Maybe this phenomenon connects to another

dominates the 2c site (1/3,2/3,0).

From the neutron

interesting thing that the radius of the transition atom

diffraction analysis, Yang etal in 197918] found that the

decreases with increasing the d electron behavior. Howe-

questions in more details. The series

Cu atom prefer to occupy the site 2c in the compounds

ver it is difficult to explain why Cu with 3dl°4s z prefers

Y(Col_.,:Cux)5. The neutron diffraction measurements

to occupy 2c site in

by Achard et al in 197919] showed that substituted Mn

expect that there is a increase of Curie temperature with

LaNQ. Comparing above three CaCu5 cases with results of ThMnl~

addition of Cu in R-Fe based compound if Cu prefers to

type compounds,we, for the first time, surprisingly find

the present rule. More detail informations maybe comes

a rule to describe the tendency of preferential site oc-

from the calculations on energy band.

atom occupies mainly the 3g site in

cupation of transition element in rare earth - transition based compounds (shown in Fig.3): Transition atoms occupy the site according to the atomic number. Atom

Y(Col-xCux)s, even though we can

occupy the site with shorter Fe-Fe distance according to

REFERENCES [1] E.A. Nesbitt, H.J. Williams, J.H. Wernick and R.C. Sherwood, J. Appl. Phys. 32(1961)342S.

with smaller atomic number or with smaller number of d electrons has a preferential tendency to occupy the site with larger transition-transition distance.

Meanwhile

[2] J.F. Herbst, J.J. Croat, F.E. Pinkerton and W.B. Yel0n, Phys.Rev. B, 29 (1984)4176

the transition atom with the larger atomic number prefers to occupy the site with shorter transition-transition

[3] R.B. Helmholdt, J.J.M. Vleggaar and K. H. J.

distance. This experimental rule can also explain why

Buschow, J. Less-Common Metal, 138(1988)Lll.

Mn prefers to 8i site and Fe for Sf site in

Y(Mnl_=Fe=)lz

compounds[10]. Recent neutron diffraction results also

[4] O. Moze, L. Pareti, M. Solzi and W.I.F. David,

gave a support to our above rule that Cr and Mn pre-

Solid Stat. Comm. 66(1988)465

8jz site with largest transition-transition distance in YzFe,_~,T~B (T=Cr,Mn)[11].

fer to occupy

A1 is always added in R-Fe or R-Co based compounds.

NdzFel4B it prefers to 8j2 site[12]. In LaNis_xAl= compounds it prefers to 3g site. In RAlsT4 (T=Cr,Mn,Fe

[5] Jifan Hu, Ziwen Dong, Yinglie Liu and Zhenxi Wang, to be published in Physica B

In

and Cu) compounds, A1 prefers to occupy 8i site [ 13,14,1~

[6] H.M. Van Noort and K.H.J. Buschow, J. LessCommon Metal 113(1985)L9

That seems that we can treat A1 like a quisi-transition atom with the smaller atomic number than that of Cr [7] J.B.A.A. Elemans and K.H.J. Buschow, Phys. Stat. prefers to the site with

larger T-T distance 4

prefers to the sits with shorter T-T distance

Sol.(a), 24(1974)393. l=

"ri(22) V(23) Cr(24) Mn(25) Fe(26) Co (27) Ni(28) Cu (29) Zn(30) 3dZ4s 2 3d34~ 3dS4s1 3dS4s 2 3d64$ 2 3d74s 2 3dS4s 2 3dlO4s1 3dl°4s 2

[8] Y.T. Yang, W.W. Ho, K.L. Yang, T.S. Tchou, S.S. Ts'eng and L. Kin, J. de Physique, C5(1979)177.

Fig.3: Tendency of preferential occupation of transition elements on crystalline sites in rare earth - transition based compounds.

[9] J.C. Achard, F. Givord, A. Percheron-Guegan, J.L. Soubeyroux and F. Tasset, J. de. Physique, C5(1979)218.

188

CRYSTALLINE SITES IN RARE EARTH

[10] Y.C. Yang, B. Kebe, W.J. James, J. Deportes and W. Yelon, J. Appl. Phys. 52(1981)2077 [11] O. Moze, L. Pareti, M. Solzi, F. Bolzoni, W.I.F. David, W.T.H. Harrison and A.W. Hewat, J. Less Common Metals, 136(1988)375. [12] Y.C. Yang, W.J. James, X.D. LI, H.Y. Chen and L.D. Xu, IEEE Trans. Magn. MAG-22 (1986)757

Vol. 85, No. 3

[13] I. Felaer and I. Nowik, J. Phys. Chem. Solids 39(1978)951.

[14] O. Moze, R.M. Ibberson, R. Caciuffo and K.H.J. Buschow, J. Less-Common Met., 166(1990)329.

[15] O. Moze, R.M. Ibberson and K.H.J. Buschow, J. Phys: Condens. Matter. 2(1990)1677