SPECIFIC HEAT ANALYSIS OF TbRhIn, DyRhIn, HoRhIn

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Nov 15, 2013 (3 years and 8 months ago)

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SPECIFIC HEAT ANALYSIS OF Tb
2
Rh
I
n
8
, D
y
2
Rh
I
n
8
, H
o
2
Rh
I
n
8


M. Ročeň,
milanroc@centrum.cz
,
Jaroslav Seifert´s Grammar school, Prague, Czech Republic

INTRODUCTION

Compounds that belong to the group with structure
R
m
TX
3m+2

(where R is rare earth



Tb/Dy/Ho in t
his
cause
, T some transition material, X is In or Ga and
m

is
1 or 2) are heavy fermion materials that shows
superconductivity. These compounds often exhibit very
complex phase diagrams with a large variety of ground
states (for example unconventional supe
rconductivity,
non
-
Fermi liquid behaviour or magnetic order. Some of
these unconventional superconductors can be found
among cer
-
based R
2
TX
8

compounds. All compounds
with the structure Ce
2
T
in
8

are heavy fermion materials.
Ce
2
RhIn
8
is an antiferromagnet, wi
th superconductivity
induced by preassure (
T
N
=2,8K,
T
c
=2K at
p
=2,5 GPa)
[M. Nicklas et al., 2003]
.
Ce
2
IrIn
8

remains a heavy
fermion paramagnet down to 50mK
[N. O. Moreno et al.,
2002]
. At temperatures lower than 0.4 K, Ce
2
CoIn
8

acts
like superconductor. An
d finally, Ce
2
PdIn
8

was also
synthesized and shows up superconductivity below 0,7K
[D. Kaczorowski et al., 2009]
.

Studies of isostructural magnetic

compounds

are
important to prospect the emergence of
f
-
electron
magnetism in Ce
2
TX
8
, becau
se

the heavy fermi
on
superconductivity in these compounds is probably
magnetically mediated. Most of those compounds order
antiferromagnetically. The only exceptions are
praseodymium
-
based compounds which remain
paramagnetic
[N. V. Hieu et al., 2005]
. Some of the basic
tend
encies in the progress of the Néel temperatures with
regard to the rare earth ion were stated together with the
bulk measurement, but the comprehensive microscopic
studies of the magnetic structure were done only for very
limited amount of compounds
(Ce
2
Rh
In
8
[W. Bao et al.,
2001]
, Tb
2
RhIn
8

[R. Lora
-
Serrano et al., 2006]
, Gd
2
IrIn
8

[E. Granado et al., 2006]

and Sm
2
IrIn
8

[C. Adriano et
al., 2007]
with the use of XMRS). Set magnetic
structures are mostly determined by appropriate
propagation, but with dissimi
lar stream of magnetic
moments which can head out of any chief
crystallographic tendency.

EXPERIMENTAL

Single crystals of
R
2
RhIn
8

were prepared by the solution
growth method from an indium flux

[
K. Uhlirova et al.,
2009
]

with starting composition
R
2
RhIn
40
.

The elements
were placed to alumina cups,
e
vacuated
up to
pressure of
10
-
8

atm.

a
nd heated up to 910°C. Then, the samples were
cooled down to 400°C
(Fig.1.). R
emaining indium was
removed by a centrifuge.

After
that

single crystals of size
2x1x0,3mm were

ob
tained.


The sample composition and homoge
i
nity were

checked
by X
-
ray powder diffraction (XRPD) and by a scanning
electron microscope (SEM) Tescan Mira I LHM
equipped with energy
-
dispersive X
-
ray dete
c
tor (EDX)
Bruker (AXS). For the analysis was used a h
igh voltage
of 10kV.

The spe
cific heat was measured by the relaxation method

using Quantum D
esign PPMS syste
m in temperature
range between 1.
8 and 300 K

and in magnetic fields up to
14 T

applied along the

c
-
axis
(Fig.

2
.

a, b, c
)




Fig. 2
a,b,c
.

Specific

heat of
R
2
RhIn
8

compounds in
the
low temperature range
.


RESULTS

All the
measurements revealed interesting magnetic
phase diagrams. All the compounds behave
aniferromagnetically (AF1) under Néel temperatures
43 K

for terbium compound, 25.3 K for the d
ysprosium
one and

for the

holmium compound under 10.8 K
. In
external magn
etic field we observed transition

to one
antiferromagnetic
phase else (AF2)

.

As we can see for



Fig. 4
.a,b,c
. Magnetic phase diagrams of studied
compounds
(
R
2
RhIn
8
)
. Data were de
termined of specific
heat measurements.


example on Fig. 1.a (Tb
2
RhIn
8
), in a measurement in
14

T, there is a leap in the heat capacity in 26.2 K which
is caused by transition to another magnetic phase (Fig.
4.a,b,c). The transition field is 11.5 T for the

terbium
compound, for the dysprosium compound is it 4.3 T and
for the holmium compound 2.5 T in temperature of 2 K.

CONCLUSIONS

We have succes
s
fully prepared and measured
Tb
2
RhIn
8
,
Dy
2
RhIn
8

and

Ho
2
RhIn
8
, the last two ones

for

the first
time ever
. They be
have antiferromagnetically under Néel
temperatures as written
above
. During

our measurement
s

we
found another antiferromagnetic

phase which was

induced by external magnetic field.

ACKNOWLEDGMENT:

This work is part of project

Voyage to

Science“

as project
No. 3

financed by Prague,
the capital of Czech republic and supported by European
social fund and by help of Jaroslav Seifert´s grammar
school and
by
Faculty
of Nuclear Sciences and Physical
Engineering of Czech Technical University in Prague.

Special tha
nks belongs to Peter Čermák and all Faculty of
Mathematics and Physics of Charles University in
Prague.

REFERENCES

1.

M. Nicklas

et al.
,
Phys.

Rev
.

B
,

67
,

020506
(R)

(2003)

2.

N. O. Moreno

et al.
, Physica B, 312
-
313, 274
(2002)

3. D. Kaczorowski
et al.
,
Phy
s.

Rev
. Lett.
, 103,
027003 (2009)

4. N. V.

Hieu
et al.
, J. Phys.

S
oc. Jp
n
., 74, 3320 (2005)

5. W. Bao
et al.
,Physical Review B, 64, 020401 (2001)

6. R. Lora
-
Serrano

et al.
, Physica B, 384, 326 (2006)

7. E. Granado

et al.
, Phys. Rev. B, 74, 214428 (2006)

8.

C. Adriano

et al.
, Phys. Rev. B, 62, 12266 (2000)


9. K. Uhlirova
et al.
,

Int. J. Mater. Res., 100, 1242
(2009)



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