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.
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-
ing 5TFe Mossbaner spectroscopy.
SlnU05 is of U,zC~s hexagonal structure  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.
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
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
CRYSTALLINE SITES IN RARE EARTH
. . . . . . .
• °°~o 1.00
Velocity (mm/s'8f~ x=1 , , , . , , ...... 8f . . . . . . 8j . . . . . . 8] ' . . . . . 8i ......
' ' ' ' [ 1
1 1 1 1 3
Fig.2: The number of iron atom occupation N at different iron site 8i, 8j and 8f in
for each iron site 8i,8j and 8f is shown in fig.2.
iron occupation on each site
= 3:4:4. That is to say the Ti atom prefers to occupy
Velocity (,mm/s! 8f ...... 8f . . . . . . ,
8j ,8j '8i
With increasing of cobalt content in compounds,for DyTiFe8Co3,
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
temperature increases rapidly with the initial replace-
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
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 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-
It is our second question.
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. 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
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
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  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.
 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
 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
compounds. Recent neutron diffraction results also
 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).
fer to occupy
A1 is always added in R-Fe or R-Co based compounds.
NdzFel4B it prefers to 8j2 site. In LaNis_xAl= compounds it prefers to 3g site. In RAlsT4 (T=Cr,Mn,Fe
 Jifan Hu, Ziwen Dong, Yinglie Liu and Zhenxi Wang, to be published in Physica B
and Cu) compounds, A1 prefers to occupy 8i site [ 13,14,1~
 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  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
 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.
 J.C. Achard, F. Givord, A. Percheron-Guegan, J.L. Soubeyroux and F. Tasset, J. de. Physique, C5(1979)218.
CRYSTALLINE SITES IN RARE EARTH
 Y.C. Yang, B. Kebe, W.J. James, J. Deportes and W. Yelon, J. Appl. Phys. 52(1981)2077  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.  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
 I. Felaer and I. Nowik, J. Phys. Chem. Solids 39(1978)951.
 O. Moze, R.M. Ibberson, R. Caciuffo and K.H.J. Buschow, J. Less-Common Met., 166(1990)329.
 O. Moze, R.M. Ibberson and K.H.J. Buschow, J. Phys: Condens. Matter. 2(1990)1677