High-field magnetization study of a Tm
2
Co
17
single crystal
A. V. Andreev,
1,
* M. D. Kuz’min,
2
Y. Narumi,
3,†
Y. Skourski,
4
N. V. Kudrevatykh,
5
K. Kindo,
3
F. R. de Boer,
2,6
and J. Wosnitza
4
1
Institute of Physics, ASCR, Na Slovance 2, 18221 Prague, Czech Republic
2
Leibniz-Institut für Festkörper- und Werkstoffforschung, PF 270116, 01171 Dresden, Germany
3
Institute for Solid State Physics, University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8581, Japan
4
Hochfeld-Magnetlabor Dresden (HLD), Forschungszentrum Dresden–Rossendorf, Dresden, 01314, Germany
5
Institute of Physics and Applied Mathematics, Ural State University, 620083 Ekaterinburg, Russia
6
Van der Waals-Zeeman Institute, University of Amsterdam, Valckenierstraat 65, 1018 XE Amsterdam, The Netherlands
Received 16 August 2009; revised manuscript received 12 February 2010; published 23 April 2010;
publisher error corrected 29 April 2010
Tm
2
Co
17
is a ferrimagnet with T
C
= 1170 K and, at 4.2 K, has a spontaneous magnetic moment M
s
= 13.4
B
/ f.u. Magnetization curves were measured on a Tm
2
Co
17
single crystal along the principal axes in
pulsed magnetic fields up to 70 T at 4.2 K. The curve along the easy 001 direction exhibits a distinct anomaly
at
0
H
cr
= 39 T, where the magnetization exhibits a stepwise rise from M
s
to M
flip
= 40.6
B
/ f.u. The observed
transition from the ferrimagnetic ground state with M
s
=17
Co
-2
Tm
to a saturated spin-flip state with
parallel orientation of the sublattice moments and M
flip
=17
Co
+2
Tm
is unusual for 3d-4 f intermetallics
because it does not proceed via an intermediate angled-sublattice state. Rather, a collinear remagnetization of
the Tm sublattice takes place: as the applied magnetic field grows, the Tm moments disorder at first, reaching
a fully disordered paramagnetic state at H = H
cr
, then they order magnetically in the opposite sense.
DOI: 10.1103/PhysRevB.81.134429 PACS numbers: 75.30.Kz, 75.30.Gw, 75.50.Gg
I. INTRODUCTION
Tm
2
Co
17
belongs to the “2-17” series of R-T intermetallic
compounds R is a rare-earth and T is one of the late 3d
transition metals Fe, Co, and Ni. The R-T intermetallics,
especially the ones with high content of the T metal, have
been extensively studied for several decades all over the
world because of their practical importance as high-
performance magnetic materials. The magnetic behavior of
the R sublattice is determined by the 4 f electrons whereas
the 3d electrons are responsible for the T-sublattice magne-
tism. The strongest exchange interaction is the 3d-3d inter-
action, which determines the high Curie temperature T
C
. The
exchange interaction between 4 f electrons is very weak and
can be neglected compared to other interactions. The 4 f -3d
interaction, although much weaker than the 3d-3d interac-
tion, is of special importance since by this interaction the
strongly anisotropic R-sublattice magnetization is coupled to
the much less anisotropic T-sublattice magnetization. In this
way, some of the R-T compounds exhibit large anisotropy
even at room temperature, one of the prerequisites for poten-
tial application of ferromagnetic R-T compounds with light
R as permanent-magnet material.
1–3
In R
2
T
17
with heavy R elements Gd-Tm, the magnetic
moments of the R and T sublattices are coupled ferrimagneti-
cally. In high magnetic fields, this antiparallel structure will
be broken and a forced-ferromagnetic state is expected.
Since R
2
T
17
compounds exhibit large magnetic anisotropy,
single crystals are strongly desirable for quantitative studies
of their magnetism. Many compounds R
2
T
17
have been pre-
pared in single-crystalline form and studied systematically in
high magnetic fields, typically up to 35–40 T.
1,2,4
For the
majority of these compounds, the preferred moment direc-
tion is located in the hexagonal basal plane of the hexagonal
crystal structure of the Th
2
Ni
17
type. If a sufficiently large
magnetic field is applied along one of the main crystallo-
graphic directions in the basal plane, field-induced transi-
tions will occur before the forced-ferromagnetic state is
reached. Observation of these transitions, which are prima-
rily based on the interplay between the strength of the ap-
plied field and the strength of the R-T interaction, requires
high magnetic fields, in the approximate field range of 20–
250 T. Transitions of this type have been found in Ho
2
Co
17
Ref. 5 and later in several other compounds. There are only
three ferrimagnetic R
2
T
17
compounds, Er
2
Co
17
, Tm
2
Co
17
,
and Tm
2
Fe
17
, in which the easy moment direction is along
the hexagonal c axis. Field-induced phase transitions should
occur in these compounds as well. Exceptionally, if the an-
isotropy proves stronger than the intersublattice exchange, an
easy-axis ferrimagnet may go over directly to the forced-
ferromagnetic state. Such a possibility is not realized in
Er
2
Co
17
, where a field-induced transition from the collinear
ferrimagnetic structure to an intermediate canted structure
has been observed at about 40 T.
6
As the field is further
increased, the forced-ferromagnetic state is approached
gradually. Compounds with Tm still remain good candidates
for finding metamagnetism. So far they have not been stud-
ied in sufficiently high fields to observe the transition.
Tm
2
Co
17
has a hexagonal crystal structure of the Th
2
Ni
17
type with two nonequivalent positions for the Tm atoms and
four positions for the Co atoms. It is a ferrimagnet with
Curie temperature T
C
=1170 K and, at T =4.2 K, it has a
spontaneous magnetic moment M
s
= 13.4
B
/ f.u. as deter-
mined in measurements on single crystals in which the maxi-
mum applied field was 15 T and no field-induced transition
was observed.
7
In this work, we present and discuss the mag-
netization curves at 4.2 K along the principal axes of a
Tm
2
Co
17
single crystal in pulsed magnetic fields up to 70 T.
II. EXPERIMENTAL
An ingot of Tm
2
Co
17
was prepared by arc melting in Ar
atmosphere. The purity of the constituting metals was
PHYSICAL REVIEW B 81, 134429 2010
1098-0121/2010/8113/1344295 ©2010 The American Physical Society 134429-1