Magneto-superconductivity of 100-atm O2-annealed RuSr2Gd1.5Ce0.5Cu2O10-δ

Article abstract of DOI:10.1016/S0921-4534(03)00625-7

Studied 100-atm O₂-annealed RuSr₂Gd_1.5Ce_0.5Cu₂O_10-δ (Ru-1222) compound crystallized in a tetragonal I4/mmm space group crystal structure. Thermo-gravimetric (TG) analysis was successfully applied to establish the oxygen content of the sample studied at 9.63 per formula unit. The DC magnetization data (M vs. T) revealed magnetic transition at ～100 K followed by superconducting transition at ～40 K. Low field (-100≤H≤100 Oe) M vs. H hysteresis loop showed a lower critical field (H_c1) value of around 25 Oe. Ferromagnetic component is evidenced at 5, 10, 20 and 40 K. Near saturation field of above 5 T is observed at 5 K. Zero-field returning moment (M_r) and zero-moment coercive field (H_c) values at 5 K are 0.35 μ_B and 250 Oe. The resistance vs. temperature (R vs. T) behaviour of the sample confirmed superconductivity at around 43 K. Superconductivity transition (T_c) is broadened under magnetic field with strong granularity like steps.

Full text of DOI:10.1016/S0921-4534(03)00625-7

Physica C 390 (2003) 233–238
www.elsevier.com/locate/physc
Magneto-superconductivity of 100-atm O2-annealed
RuSr2Gd1:5Ce0:5Cu2O10ꢀd
a,
a
b
b
V.P.S. Awana *, E. Takayama-Muromachi , M. Karppinen , H. Yamauchi
a
Superconducting Materials Center, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
b
Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226-8503, Japan
Received 2 December 2002; received in revised form 5 December 2002; accepted 26 December 2002
Abstract
Studied 100-atm O2-annealed RuSr2Gd1:5Ce0:5Cu2O10ꢀd (Ru-1222) compound crystallized in a tetragonal I4/mmm
space group crystal structure. Thermo-gravimetric (TG) analysis was successfully applied to establish the oxygen
content of the sample studied at 9.63 per formula unit. The DC magnetization data (M vs. T) revealed magnetic
transition at ꢁ100 K followed by superconducting transition at ꢁ40 K. Low field (ꢀ100 6 H 6 100 Oe) M vs. H
hysteresis loop showed a lower critical field (Hc1) value of around 25 Oe. Ferromagnetic component is evidenced at 5,
10, 20 and 40 K. Near saturation field of above 5 T is observed at 5 K. Zero-field returning moment (Mr) and zero-
moment coercive field (Hc) values at 5 K are 0:35lB and 250 Oe. The resistance vs. temperature (R vs. T) behaviour of
the sample confirmed superconductivity at around 43 K. Superconductivity transition (Tc) is broadened under magnetic
field with strong granularity like steps.
Ó 2003 Elsevier Science B.V. All rights reserved.
PACS: 74.25.Ha; 74.72.Jt; 75.25.þz; 75.30.Cr
1. Introduction
ied for their transport properties already in 1995
[6], but magnetic characterization had not been
carried out until recently [1–5]. Both Ru-1222 and
Ru-1212 phases are structurally related to the
CuA2QCu2O7ꢀd [Cu-1ðAÞ2ðQÞ12 or Cu-1212, e.g.
CuBa2YCu2O7ꢀd] phase with Cu in the charge
reservoir replaced by Ru such that the Cu–O chain
is replaced by a RuO2 sheet. In the Ru-1222 struc-
ture furthermore, a three-layer fluorite-type block
instead of a single oxygen-free R ( ¼ rare earth
element) layer is inserted between the two CuO2
planes of the Cu-1212 structure [7]. In both Ru-
1222 and Ru-1212 replacement of Cu in the charge-
reservoir block by the higher-valent Ru increases
the overall oxygen content [1–5].
Coexistence of superconductivity and magne-
tism in ruthenium copper oxides was reported for
the first time for RuSr2(Gd,Sm,Eu)1:6Ce0:4Cu2-
O
10ꢀd [Ru-1ðSrÞ2ðGd;Sm;Eu;CeÞ22 or Ru-1222] [1,2], and
later for Ru-1ðSrÞ2ðGdÞ12 (Ru-1212) [3–5]. Both ru-
thenium copper oxides were synthesized and stud-
* Corresponding author. Address: Crystal Growth and
Characterization (CGC) Section, National Physical Labora-
tory, K.S. Krishnan Marg, New Delhi 110012, India. Fax: +91-
11-25726938.
E-mail address: awana@csnpl.ren.nic.in (V.P.S. Awana).
0921-4534/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0921-4534(03)00625-7

234
V.P.S. Awana et al. / Physica C 390 (2003) 233–238
Substantial work has been carried out on the
in the temperature range of 5–300 K using a four-
point-probe technique.
Ru-1212 phase. The magnetic structure was stud-
ied through neutron diffraction experiments [8].
Electromicroscopic works revealed a superstruc-
ture along the a–b plane due to tilting of RuO6
octahedra [9], which was further confirmed from
neutron diffraction studies [10]. The appearance of
bulk superconductivity at low temperatures in Ru-
1212 was initially criticised [11] which was later
refuted [12,13]. Also not all single phase Ru-1212
exhibit the co-existence of superconductivity and
magnetism [14]. Worth mentioning is the fact that
there exist contradictory reports on heat capacity
data under magnetic fields, i.e. CP ðH; T Þ [15,16].
Eventhough ‘‘magneto-superconductivity’’ was
first realised in Ru-1222, a lot still remain about
the physical characterization. In particular the
magnetic structure from neutron diffraction ex-
periments and the microstructural details are still
lacking. In present contribution we report the en-
hancement of the superconductivity with high-
pressure oxygen annealing of Ru-1222, and discuss
its various physical properties. Thermo-gravimet-
ric (TG) analysis of the compound in 95% Ar and
5% H2 was used to determine the oxygen content
of the studied sample.
3. Results and discussion
3.1. X-ray diffraction and TG––phase formation and
phase decomposition
As-synthesized Ru-1222 copper oxide crystal-
lises in a tetragonal structure of space group
ꢀ
I4/mmm with a ¼ b ¼ 3:8327ð7Þ
A
and c ¼
ꢀ
28:3926ð8Þ A. An XRD pattern for the oxide is
shown in Fig. 1. A trace of SrRuO3 is seen, as
marked on the pattern. Presence of small amounts
of SrRuO3 and/or GdSr2RuO6 in Ru-1222 mate-
rial is seen earlier also in various reports [1,2,
18,19]. In fact our currently studied sample seems
to be of better quality in terms of phase purity. Ru-
1222 is structurally related to the CuA2QCu2O7ꢀd
[Cu-1ðAÞ2ðQÞ12 or Cu-1212, e.g. CuBa2YCu2O7ꢀd
phase with Cu in the charge reservoir replaced by
Ru such that the Cu–O chain is replaced by a
RuO2 sheet, furthermore, a three-layer fluorite-
]
2. Experimental
The RuSr2Gd1:5Ce0:5Cu2O10ꢀd (Ru-1222) sam-
ple was synthesized through a solid-state reaction
route from RuO2, SrO2, Gd2O3, CeO2 and CuO.
Calcinations were carried out on the mixed pow-
der at 1000, 1020, 1040 and 1060 °C each for 24 h
with intermediate grindings. The pressed bar-
shaped pellets were annealed in a flow of high-
pressure oxygen (100 atm) at 420 °C for 100 h and
subsequently cooled slowly to room temperature
[17]. X-ray diffraction (XRD) patterns were ob-
tained at room temperature (MAC Science:
MXP18VAHF22; CuKa radiation). TG analysis
(MAC Science: TG-DTA 2000 S) was carried out
in an 95% Ar and 5% H2 atmosphere to check
the oxygen content. Magnetization measurements
were performed on a SQUID magnetometer (Quan-
tum Design: MPMS-5S). Resistivity measurements
under applied magnetic fields of 0–7 T were made
Fig. 1. XRD pattern observed for Ru-1222, inset shows the TG
curve for the same.

V.P.S. Awana et al. / Physica C 390 (2003) 233–238
235
type block instead of a single oxygen-free R ( ¼ rare
earth element) layer is inserted between the two
CuO2 planes of the Cu-1212 structure [7].
superconductivity starts with the superconductiv-
ity transition onset temperature (Tconset) at 47 K
and the zero-resistance temperature (TcR¼0) at 43 K.
In fact the R vs. T plot above Tconset is nearly
temperature independent. The R vs. T behaviour
under an applied field of 7 T is nearly the same as
that of 0 T above Tconset. However in 7 T field TcR¼0
is observed only at 12 K. In intermediate fields of
1, 3 and 5 T, TcR¼0 were seen respectively at 18, 16
and 14 K, respectively. The TcR¼0 value is decreased
fast from 43 K to around 18 K with applied field of
1 T, and is later not affected much with higher
fields of 3, 5 and 7 T. Also seen is a strong step like
shoulder in the R vs. T curve at 1 T, the origin of
which may be related to the intra-grain phase-lock
transition. The intra-grain phase-lock transition
and the appearance of bulk superconductivity be-
low the length scale of grain size (typically 2–6 lm)
is discussed in detail for another magneto-super-
conductor RuSr2EuCu2O8 [21]. The Tconset of the
compound remains nearly unchanged with H. For
conventional high-temperature superconductors
(HTSC) Tconset remains nearly the same under all
possible applied fields, but TcR¼0 decreases and the
transition width (Tconset ꢀ TcR¼0) increases. In the
inset of Fig. 2 the magneto-resistance (MR) data
of the present Ru-1222 compound is shown at
various temperatures and fields, revealing a small
negative MR effect in the whole temperature
range. Below 100 K the degree of MR is nearly the
same in all applied fields and the nature of the MR
effect is of the tunnelling-magneto-resistance type
as judged from the curve shape. Also note that the
MR behaviour of the present Ru-1222 sample is
different from that of Ru-1212. Ru-1212 had ex-
hibited systematic changes in sign of MR at vari-
ous T and H [4,16].
TG curve of the Ru-1222 compound being re-
corded in 95% Ar and 5% H2 atmosphere with 1
°C per min heating schedule is shown in the inset
of Fig. 1. Upon heating in flowing H2/Ar gas Ru-
1222, releases oxygen while decomposing to Ru
metal, Cu metal and oxides of Sr, Gd and Ce in
two distinct steps about 300 and 450 °C. Owing to
the sharpness of the weight loss behavior such
reductive decomposition carried out in a thermo-
balance may be utilized in precise oxygen content
determination for the compound [20]. For the Ru-
1222 phase, several repeated experiments revealed
that the oxygen content of presently studied 100-
atm O2-annealed samples was 9.63(5) per formula
unit.
3.2. Electrical and magneto-transport results
Fig. 2 shows the resistance vs. temperature plots
(R vs. T) in 0, 1, 3, 5 and 7 T fields for Ru-1222.
The R vs. T behaviour in zero field is metallic down
to 270 K and semiconducting below 270 K until
3.3. Superconductivity and magnetism
Fig. 3 shows the magnetic susceptibility (v) vs.
T behaviour in the temperature range of 5–200 K
for Ru-1222 sample under applied fields of 5, 10
and 50 Oe, measured in both zero-field-cooled
(ZFC) and field-cooled (FC) modes. In an applied
field of 5 Oe, the v vs. T show the branching of
ZFC and FC curves at around 90 K (Tirr), a step
like structure in both at around 40 K (Tc) and
Fig. 2. R vs. T plots in 0, 1, 3, 5 and 7 T fields for Ru-1222, in
inset is shown the MR at various T and H for the same.

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V.P.S. Awana et al. / Physica C 390 (2003) 233–238
Fig. 4. M–H loop for Ru-1222 at 5 K with ꢀ100 6 H 6 100 Oe.
Fig. 3. v vs. T plot for Ru-1222 in both ZFC and FC modes
with H ¼ 5, 10 and 50 Oe, the inset shows the same for
H ¼ 1000 and 10,000 Oe.
again after further magnetic characterization in
next section.
further a diamagnetic transition around 40 K (Td)
in the ZFC magnetization. Though the ZFC and
FC magnetization branching is seen at around 90
K, the magnetic behaviour starts deviating from
normal paramagnetic relation at much higher T
say 160 K. The characteristic temperatures Tirr, Tc,
and Tmag are weakly dependent on H < 100 Oe.
For higher H > 100 Oe, both ZFC and FC are
merged with each other, and only Tmag could be
seen, see inset Fig. 3. This is in general agreement
with earlier reports [1,2,21,22]. In fact no ZFC–FC
branching is observed down to 5 K in both 1000
and 10,000 Oe fields and both the anomaly and the
irreversibility in both ZFC and FC branches look
to be washed out.
To elucidate the magnetic property of Ru-1222
we show isothermal magnetization (M) vs. applied
field (H) behaviour at various T (Fig. 5). Clear M
vs. H loops are seen at 5, 10, 20 and 40 K. The
applied fields are in the range of )2000 6 H 6
The ZFC curve did not show any diamagnetic
transition (Td) in H > 50 Oe. The magnetization
data at H ¼ 10 Oe, show nearly the same charac-
teristics as for H ¼ 5 Oe. A low field ()100 6
H 6 100 Oe) M vs. H loop for currently studied
Ru-1222 compound is shown in Fig. 4. Interest-
ingly the diamagnetic signal starts decreasing
above applied fields of 25 Oe, and turns to zero at
say 40 Oe. The compound seems to have a lower
critical field (Hc1) of around 25 Oe. Interestingly
the M vs. H plot shown in Fig. 4 does not appear
to be a normal HTSC case. We will discus the low
field ()100 6 H 6 100 Oe) M vs. H loop of Fig. 4
Fig. 5. M–H loops for Ru-1222 at 5, 10, 20 and 40 K with
ꢀ2000 6 H 6 2000 Oe. The upper and lower insets of the figure
show Mrem vs. T and Hc vs. T plots for the same.

V.P.S. Awana et al. / Physica C 390 (2003) 233–238
237
2000. At 5 K, the returning moment (Mrem) i.e. the
value of magnetization at zero returning field and
the coercive filed (Hc) i.e. the value of applied re-
turning field to get zero magnetization are re-
spectively 0:35lB and 250 Oe. Worth mentioning is
the fact that Gd (magnetic rare earth) in the
compound orders magnetically below 2 K and Ce
is known to be in tetravalent non-magnetic state
hence the Mrem and Hc arising from the ferromag-
netic hysteresis loops do belong to Ru only. Hys-
teresis loops are not seen for M vs. H plots above
80 K. For various hysteresis loops being observed
from M vs. H plots below 80 K, the values of both
Mrem and Hc decrease with T. The plots for both
are shown in upper and lower insets of Fig. 5.
Both Mrem and Hc of 0:35lB and 250 Oe being
observed for Ru-1222 are much higher than re-
ported for other magneto-superconductor Ru-
1212 [5,12]. For Ru-1212 the hysteresis loops are
reported quite narrow with Mrem and Hc of 0:085lB
and 10 Oe respectively. This indicates that in Ru-
1222 the ferromagnetic domains are less aniso-
tropic and more rigid.
Fig. 6. M–H plot for Ru-1222 compound at T ¼ 5 K, the ap-
plied field are in the range of )70,000 6 H 6 70,000 Oe. The
inset shows the theoretical plot for paramagnetic Gd contri-
bution to the system.
The isothermal magnetization as a function of
magnetic field at 5 K with higher applied fields;
70,000 6 H 6 70,000 Oe is shown in Fig. 6. The
saturation of the isothermal moment appears to
occur above say 5 T applied fields. The contribu-
tion from the ferromagnetic component starts to
appear below 100 K. The presence of the ferro-
magnetic component is confirmed by hysteresis
loops being observed at 5, 10, 20 and 40 K in the
M vs. H plots, (see Fig. 5). Ru spins order mag-
netically above say 100 K with a ferromagnetic
component within (Mrem, Hc ¼ 0:35lB, 250 Oe) at 5
K. As far the value of higher field (>5 T) satura-
tion moment is concerned, one cannot without
ambiguity extract the value for Ru contribution.
Basically besides paramagnetic Gd contribution at
5 K, the contribution from Cu cannot be ignored,
which in an under-doped HTSC compound con-
tributes an unknown paramagnetic signal to the
system. For paramagnetic Gd contribution the
theoretical plot at 5 K is shown in the inset of Fig.
6. After taking out the Gd contribution from Ru-
1222 effective moment in Fig. 6, a value of ꢁ0:75lB
is obtained for effective near saturation moment of
Ru. This value is less than for Ru5þ low spin state
ordering. In Ru-1212 compound, based on various
magnetization data the Ru5þ state is reported with
an effective saturation moment of nearly 1lB [3],
which ironically differs with more recent magnetic
analysis [23].
Superconductivity is seen in terms of diamag-
netic transition at below Td, and Tc (R ¼ 0) at
slightly higher temperature. It is known earlier
that due to internal magnetic field, these com-
pounds are in a spontaneous vortex phase even
in zero external field [24]. For Td < T < Tc the
compound remains in mixed state. Hence though
R ¼ 0 is achieved at relatively higher tempera-
tures the diamagnetic response is seen at much
lower T and that also in quite small applied mag-
netic (Hc1 < 25 Oe) fields. Now we can understand
the M vs. H loop being shown in Fig. 4. As dis-
cussed in previous section clear ferromagnetic
component is seen in the compound at 5 K. Hence
at 5 K both ferromagnetic and the superconduct-
ing hysteresis loops are present in the M vs. H
magnetization data, and at low applied fields viz.
)100 6 H 6 100 Oe, the compound simply exhibit
the superimposition of the both, which is the case
in Fig. 4.

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V.P.S. Awana et al. / Physica C 390 (2003) 233–238
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Good quality RuSr2Gd1:5Ce0:5Cu2O10ꢀd (Ru-
1222) is synthesized through solid state reaction
route and superconductivity is achieved in the
same up to 43 K with 100-atm O2 annealing. Ru-
1222 releases oxygen in two distinct steps at about
300 and 450 °C. The compound shows the clear
magneto-superconductivity characteristics, in terms
of bulk superconductivity and the presence of
ferromagnetism at low T , below 40 K. At 5 K,
the Mrem and Hc ¼ 0:35lB and 250 Oe are obtained
for the ferromagnetic component in the compound.
The resistance vs. temperature (R vs. T) behav-
iour of the sample confirmed superconductivity at
around 43 K, which is broadened under magnetic
field with strong granularity like steps.
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V.P.S.A. acknowledges the support of Prof. E.
Takayama-Muromachi for providing him with the
NIMS postdoctoral fellowship to work in NIMS.
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