Magnetic behavior in a series of cerium ternary intermetallics:
Ce
2
T
2
In „T Ni, Cu, Rh, Pd, Pt, and Au…
D. Kaczorowski*
W. Trzebiatowski Institute for Low Temperature and Structure Research, Polish Academy of Sciences,
P.O. Box 937, 50-950 Wroclaw, Poland
and Institut fu ¨r Physikalische Chemie, Universita ¨t Wien, Wa ¨hringerstraße 42, A-1090 Wien, Austria
P. Rogl and K. Hiebl
Institut fu ¨r Physikalische Chemie, Universita ¨t Wien, Wa ¨hringerstraße 42, A-1090 Wien, Austria
Received 14 February 1996; revised manuscript received 2 May 1996
A group of ternary cerium compounds Ce
2
T
2
In T =Ni, Cu, Rh, Pd, Pt, and Au has been synthesized. As
found from single-crystal and powder x-ray-diffraction studies, all these phases crystallize in a primitive
tetragonal structure of the Mo
2
FeB
2
type. Magnetic measurements magnetization, dc and ac susceptibility
have revealed the physical properties of these intermetallics to be mainly governed by the 4 f - d hybridization.
Depending on the filling of the transition metal d band the ground state in Ce
2
T
2
In changes from a nonmag-
netic to a well localized magnetic regime. It was proved that Ce
2
Ni
2
In and Ce
2
Rh
2
In are intermediate-valence
systems, Ce
2
Pt
2
In is a strongly temperature-dependent paramagnet, whereas Ce
2
Cu
2
In, Ce
2
Pd
2
In, and
Ce
2
Au
2
In order magnetically at low temperatures. Measurements of the electrical resistivity have corroborated
the intermediate-valence behavior in Ce
2
Ni
2
In and Ce
2
Rh
2
In. In turn, the resistivity of the remaining ternaries
studied was found to be determined by an interplay of Kondo scattering and crystal-field effects. For Ce
2
Pt
2
In
which behaves like a spin-fluctuating system due to strong Kondo-type interactions a nonmagnetic heavy-
fermion ground state probably occurs. S0163-18299608134-9
I. INTRODUCTION
Recently a series of ternary actinoid compounds with the
composition An
2
T
2
M An =U, Np; T =3 d -, 4 d -, 5 d -
transition metal; M =In, Sn, crystallizing in the tetragonal
Mo
2
FeB
2
-type structure an ordered derivative of the
U
3
Si
2
-type structure, has been discovered.
1–3
As a result of
intensive experimental
2–8
and theoretical
9–12
studies of these
materials it was established that their electronic properties
are mainly determined by the hybridization of the 5 f states
with the d states of transition elements. As for many other
families of light actinoid intermetallics, the behavior in the
An
2
T
2
M compounds was found to change gradually from a
nonmagnetic to a magnetic ground state when moving from
the left to the right of a transition-metal row.
7,13
Interest-
ingly, most of the uranium 2:2:1 phases exhibit at low tem-
peratures a strong enhancement in the electronic coefficient
of the specific heat values up to 830 mJ/mole K
2
as ob-
served for U
2
Pt
2
In
5
and this feature in conjunction with the
characteristic magnetic and electrical properties of these
compounds may support their classification as heavy-
fermion systems.
5,9,10
In contrast to the extensively studied actinoid intermetal-
lics with the 2:2:1 stoichiometry only very little is known up
to date about the corresponding rare-earth-based materials.
This fact has motivated us to start a systematic investigation
of the Ce
2
T
2
In compounds. Our choice of cerium-based
phases is due to a common tendency of this element to show
anomalous physical behavior in its binary or ternary interme-
tallics. Although already in 1990 the formation of Ce
2
Ni
2
In
and Ce
2
Cu
2
In was described by Kalychak et al.,
14
the mag-
netic properties of these two compounds were not studied at
that time. More recently Hulliger and Xue
15
synthesized the
Ce
2
Pd
2
In indide and found that it is ferromagnetic below
T
c
=4 K. This finding has subsequently been confirmed by
Gordon et al.
16
who also reported on the nonmagnetic prop-
erties of Ce
2
Ni
2
In. Already in the course of our present study
two further publications by Hulliger appeared which ad-
dressed the synthesis of Ce
2
Pt
2
In Ref. 17 and Ce
2
Rh
2
In.
18
The first compound was briefly mentioned to be paramag-
netic down to 1.5 K Ref. 17 and for the latter a nonmag-
netic ground state was claimed
18
due to the presence of Ce
4+
ions.
In the present paper we give an extended survey of the
physical behavior in the Ce
2
T
2
In intermetallics with T =Ni,
Cu, Rh, Pd, Pt, and Au. We report here on the crystal struc-
ture refinements from x-ray data and present the results of
detailed magnetization, dc susceptibility, ac susceptibility,
and electrical resistivity measurements performed on poly-
crystalline samples of Ce
2
T
2
In. In the discussion we empha-
size the role of interactions between the cerium 4 f electrons
and the d electrons of neighboring transition-metal atoms in
the magnetic moment formation in the compounds studied.
II. EXPERIMENTAL DETAILS
Polycrystalline samples of La
2
T
2
In and Ce
2
T
2
In were pre-
pared by arc melting the appropriate amounts of the constitu-
ent elements in a titanium gettered argon atmosphere. The
buttons were turned over and remelted several times to en-
sure a good homogeneity. Weight losses after meltings were
always smaller than 0.5 mass%. No further heat treatment
was given to the ingots except for Ce
2
T
2
In, T =Ni, Rh, Pd,
which were subsequently wrapped with molybdenum foil,
sealed in evacuated quartz tubes and annealed at 650 °C for
two weeks. All the samples obtained as cast and annealed
PHYSICAL REVIEW B 1 OCTOBER 1996-II VOLUME 54, NUMBER 14
54 0163-1829/96/5414/989112/$10.00 9891 © 1996 The American Physical Society