The evidence of a new magnetic anomaly in Zn-doped LSCO cuprates
The investigations of low-temperature heat capacity in pure (y = 0) and Zn-doped La₁,₈₄Sr₀,₁₆Cu₁–yZnyO₄ samples (y = 0.033 and 0.06) have been performed in the interval of 1.8–60 K by a method of high-precision pulsed differential calorimetry, providing the measurements under the equilibrium conditi...
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Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
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| Цитувати: | The evidence of a new magnetic anomaly in Zn-doped LSCO cuprates / M.M. Nadareishvili, K.A. Kvavadze // Физика низких температур. — 2010. — Т. 36, № 3. — С. 268-271. — Бібліогр.: 11 назв. — англ. |
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irk-123456789-1169612017-05-19T03:02:28Z The evidence of a new magnetic anomaly in Zn-doped LSCO cuprates Nadareishvili, M.M. Kvavadze, K.A. Низкотемпеpатуpный магнетизм The investigations of low-temperature heat capacity in pure (y = 0) and Zn-doped La₁,₈₄Sr₀,₁₆Cu₁–yZnyO₄ samples (y = 0.033 and 0.06) have been performed in the interval of 1.8–60 K by a method of high-precision pulsed differential calorimetry, providing the measurements under the equilibrium conditions, in contrast to commonly used differential scanning calorimeters. For these systems a new heat capacity anomaly was observed in the nonsuperconducting state, which is related with Zn impurities and has the form of one wide peak. The anomaly does not show a phonon character as it strongly shifts towards the higher temperatures with the increase of Zn content, which is characteristic for the magnetic anomaly. Anomaly increases almost linearly with the impurity concentration. 2010 Article The evidence of a new magnetic anomaly in Zn-doped LSCO cuprates / M.M. Nadareishvili, K.A. Kvavadze // Физика низких температур. — 2010. — Т. 36, № 3. — С. 268-271. — Бібліогр.: 11 назв. — англ. 0132-6414 PACS: 74.72.–h, 74.25.Bt http://dspace.nbuv.gov.ua/handle/123456789/116961 en Физика низких температур Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
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Низкотемпеpатуpный магнетизм Низкотемпеpатуpный магнетизм |
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Низкотемпеpатуpный магнетизм Низкотемпеpатуpный магнетизм Nadareishvili, M.M. Kvavadze, K.A. The evidence of a new magnetic anomaly in Zn-doped LSCO cuprates Физика низких температур |
| description |
The investigations of low-temperature heat capacity in pure (y = 0) and Zn-doped La₁,₈₄Sr₀,₁₆Cu₁–yZnyO₄ samples (y = 0.033 and 0.06) have been performed in the interval of 1.8–60 K by a method of high-precision pulsed differential calorimetry, providing the measurements under the equilibrium conditions, in contrast to commonly used differential scanning calorimeters. For these systems a new heat capacity anomaly was observed in the nonsuperconducting state, which is related with Zn impurities and has the form of one wide peak. The anomaly does not show a phonon character as it strongly shifts towards the higher temperatures with the increase of Zn content, which is characteristic for the magnetic anomaly. Anomaly increases almost linearly with the impurity concentration. |
| format |
Article |
| author |
Nadareishvili, M.M. Kvavadze, K.A. |
| author_facet |
Nadareishvili, M.M. Kvavadze, K.A. |
| author_sort |
Nadareishvili, M.M. |
| title |
The evidence of a new magnetic anomaly in Zn-doped LSCO cuprates |
| title_short |
The evidence of a new magnetic anomaly in Zn-doped LSCO cuprates |
| title_full |
The evidence of a new magnetic anomaly in Zn-doped LSCO cuprates |
| title_fullStr |
The evidence of a new magnetic anomaly in Zn-doped LSCO cuprates |
| title_full_unstemmed |
The evidence of a new magnetic anomaly in Zn-doped LSCO cuprates |
| title_sort |
evidence of a new magnetic anomaly in zn-doped lsco cuprates |
| publisher |
Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України |
| publishDate |
2010 |
| topic_facet |
Низкотемпеpатуpный магнетизм |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/116961 |
| citation_txt |
The evidence of a new magnetic anomaly in Zn-doped LSCO cuprates / M.M. Nadareishvili, K.A. Kvavadze // Физика низких температур. — 2010. — Т. 36, № 3. — С. 268-271. — Бібліогр.: 11 назв. — англ. |
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Физика низких температур |
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2025-07-08T11:23:09Z |
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2025-07-08T11:23:09Z |
| _version_ |
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| fulltext |
© M.M. Nadareishvili and K.A. Kvavadze, 2010
Fizika Nizkikh Temperatur, 2010, v. 36, No. 3, p. 268–271
The evidence of a new magnetic anomaly
in Zn-doped LSCO cuprates
M.M. Nadareishvili and K.A. Kvavadze
E. Andronikashvili Institute of Physics, 6 Tamarashvili Str., Tbilisi 0177, Georgia
E-mail: m.nadareishvili@aiphysics.ge;
mnadarei@gmail.com
Received July 21, 2009, revised October 12, 2009
The investigations of low-temperature heat capacity in pure (y = 0) and Zn-doped La1.84Sr0.16Cu1–yZnyO4
samples (y = 0.033 and 0.06) have been performed in the interval of 1.8–60 K by a method of high-precision
pulsed differential calorimetry, providing the measurements under the equilibrium conditions, in contrast to
commonly used differential scanning calorimeters. For these systems a new heat capacity anomaly was observed
in the nonsuperconducting state, which is related with Zn impurities and has the form of one wide peak. The
anomaly does not show a phonon character as it strongly shifts towards the higher temperatures with the increase
of Zn content, which is characteristic for the magnetic anomaly. Anomaly increases almost linearly with the
impurity concentration.
PACS: 74.72.–h Cuprate superconductors;
74.25.Bt Thermodynamic properties.
Keywords: differential calorimetry, LSCO, HTSC magnetic properties.
1. Introduction
The unsolved problem connected with the doping of
HTSC cuprates by Zn is the magnetism of CuO2 planes. In
particular, though Zn is a nonmagnetic impurity, in the
volume magnetization of HTSC cuprate YBa2Cu3O7–δ at
the doping with Zn, a Curie-like term with the efficient
magnetic moment Peff ≈ 1 μB is observed [1], which is
connected with this impurity. NMR investigations of 63Cu
showed that the mentioned effect is connected with the
development of staggered magnetic moments induced by
zinc and located in vicinity of each Zn site of Cu [2]. It
was also shown that the contribution to the volume
magnetization made by zinc can be explained by these
induced magnetic moments. According to the earlier
investigations of YBa2Cu3O7–δ cuprates doped by zinc, the
Curie’s law was fulfilled [1], giving the evidence of the
absence of interaction among the efficient magnetic
moments induced by zinc even at high concentrations of
Zn, when the distance between the impurities was less than
the typical diameter of staggered regions, that seemed
surprising. More exact magnetic measurements using
SQUIDs allowed to record the fulfillment of Curie–Weiss
law with a low value of temperature θ [3], giving the
evidence of the existence of interaction among these
moments.
Thermodynamic investigations of HTSC cuprates were
carried out, mainly, by differential scanning calorimeters
(DSC) [4,5]. The differential method was used for reduc-
ing large phonon contributions to the experimentally mea-
sured difference in heat capacities of the sample and the
reference, in order to make it possible to observe directly
the fine thermal effects such as the uncompensated elect-
ron heat capacity and magnetic excitations. It should be
noted that in DSC a continuous heating of samples is used
and, hence, the measurements are made under the condi-
tions being quasi-equilibrium. These investigations were
mainly dealt with the study of the properties of HTSC
electron heat capacity. The plots show well the jumps of
electron heat capacity at superconducting transitions, as
well as the existence of magnetic term in the heat capacity
of Zn-doped yttrium cuprates YBa2(Cu1-xZnx)3O7 with the
peak at about 5 K [4].
As for the investigations of HTSC heat capacity of
cuprates by conventional heat pulse technique under the
equilibrium conditions, they were carried out at the tem-
perature lower than 10 K, as above 10 K the phonon
contribution to the heat capacity of the sample becomes
larger and makes it impossible to measure precisely the
electron heat capacity and other «fine effects». In
Refs. 6, 7 at the introduction of Zn in La2–xSrxCuO4, the
The evidence of a new magnetic anomaly in Zn-doped LSCO cuprates
Fizika Nizkikh Temperatur, 2010, v. 36, No. 3 269
magnetic contribution was observed to the heat capacity of
these samples, which on the plots of the linear term of heat
capacity γ ( = Cel/T) was revealed as a bend upwards at the
temperature lower than 3.5 K. The value of this anomaly
increased with the increase of the concentration of Zn
impurity.
The subject of the present paper is the precise calori-
metric study of Zn-doped LSCO cuprates both in equilib-
rium conditions and in temperature wide range.
2. Experiment
We have performed the measurement of low-tem-
perature heat capacity on the pure and Zn doped LSCO
samples by the method of pulsed differential calorimetry
(PDC). At present, the most sensitive and, hence, the most
commonly used calorimeters are the differential scanning
calorimeters. However, these devices have one significant
disadvantage — they measure the difference in heat capa-
city between the studied sample and the reference sample
under the nonequilibrium conditions, as the heat capacity
difference was measured in the continuous heating regime.
We have developed a new method of calorimetry [8], on
the basis of which the high-sensitive differential calori-
meter of a new type — Pulsed Differential Calorimeter
was created [9]. By this calorimeter the high precision
measurements of the anomaly of low-temperature heat
capacity were made in different substances [9,10]. This
calorimeter can make the measurements with a very high
sensitivity under equilibrium conditions, as the measure-
ment of the heat capacity difference was carried out in the
pulsed heating regime. It combines the high sensitivity of
the modern differential calorimeters of continuous heating
type and the high accuracy of the classical pulsed calo-
rimeters. The difference in heat capacity ΔC between the
studied and the reference samples, makes, at its maximum,
a very small (~1%) part of the heat capacity of the sample
and is within the error of measurements of the calorimeters
measuring the absolute heat capacities. The relative error
δC/C ≈ 10–4, where δC is the error of measurement of ΔC,
and C is the absolute heat capacity of the sample.
The samples La1.84Sr0.16Cu1–yZnyO4 were fabricated at
Sussex University by a standard solid-state reaction in
which the initial combination of the constituent chemical
compounds was made by solid state mixing, and then the
samples were sintered at the temperature of 1030 K while
being subjected to a high pressure. Subsequent measure-
ments of the susceptibility showed that the samples with
y = 0.033 and 0.06, did not display the superconducting
transitions for temperatures down to 4.2 K, being the
lowest temperature in our measurements of susceptibility.
On the other hand, the sample with y = 0 showed the
superconducting transition at the temperature of 38 K. The
samples had the cylindrical form, the diameter ~ 20 mm
and the thickness ~ 3 mm; the mass of each sample was ~4 g.
3. Results and discussion
The heat capacity C(y,T) of La1.84Sr0.16Cu1–yZnyO4
systems above 3.5 K is the sum of electron (hole) Cel(y,T)
and phonon Cph(y,T) contributions [6]. In its turn, Cel(y,T) =
= γ(y)T + CS(y,T), where γ(y) is the coefficient of linear
term of Cel, CS(y,T) is the heat capacity of superconducting
electrons. As a result:
C(y,T) = γ(y)T + CS(y,T) + Cph(y,T) . (1)
Difference in heat capacity between the sample under
investigation and the reference sample with the different
amount (y1, y2 ) of Zn is equal to
ΔC(y2,y1,T) = Δγ(y2,y1)T + ΔCS(y2,y1,T) + ΔCph(y2,y1,T),
(2)
where
Δγ(y2,y1) = γ(y2) – γ(y1),
ΔCS(y2,y1,T) = CS(y2,T) – CS(y1,T),
ΔCph(y2,y1,T) = Cph(y2,T) – Cph(y1,T).
Substitution of Zn for Cu does not affect the pho-
non heat capacity, as the masses and ionic radiuses of Zn
and Cu are equal, and thus we can consider that
Cph(y2,T) – Cph(y1,T) = 0 [6]. If the sample under investi-
gation is superconducting with y2 = 0 and the reference
sample is nonsuperconducting with y1 = yc (yc = 0.033 is
the critical (minimum) concentration of Zn, when super-
conductivity is suppressed), i.e., CS(y1,T) = 0, and Eq. (2)
gives
ΔC(0,y1,T) – Δγ(0,y1)T = CS(0,T) . (3)
Using the high-precision PDC technique, the heat
capacity difference ΔC (0,y1,T) between the supercon-
ducting sample under investigation La1.84Sr0.16CuO4
(y = 0) and the nonsuperconducting reference sample
La1.84Sr0.16Cu0.967Zn0.033O4 (y = 0.033) was measured in
the low-temperature interval of 1.8–60 K under the equilib-
rium conditions. The difference between the coefficients of
linear term Δγ(0,y1) was estimated in a usual way by plott-
ing the generally used relation ΔC(0,y1,T)/T = f(T2) [6] on
the basis of the experimental data ΔC(0,y1,T) in the 3.5–8 K
temperature interval. By using the extrapolation at T → 0 it
was found that |Δγ(0,y1)| = 8.4 mJ/(mol·K2). As γ(0) = 0
[9], we have γN ≡ |γ(yc)| = |γ(0.033)| = 8.4 mJ/(mol·K2).
Curve 1 in Fig. 1 (open circles) shows ΔC(0,y1,T) –
( )1– 0, y TγΔ dependence for molar heat capacity difference
between La1.84Sr0.16CuO4 and La1.84Sr0.16Cu0.967Zn0.033O4
(y1 = 0.033 reference sample). One can note the appea-
rance of the unphysical (negative) region for CS(0,T). To
clarify the situation, we measured the heat capacity differ-
ence ΔC(y2,y1,T) between two nonsuperconducting samples
with different content of Zn (y2 = 0.033 — the investigated
sample and y1 = 0.06 — the reference sample). As the both
M.M. Nadareishvili and K.A. Kvavadze
270 Fizika Nizkikh Temperatur, 2010, v. 36, No. 3
samples are nonsuperconducting, CS(y,T) = 0 and, if
Eq. (1) presenting the heat capacity is valid, Eq. (2) shows
that ΔC(y2,y1,T) – Δγ(y2,y1)T difference should be zero.
However, as Fig. 2 shows, this dependence is of a complex
form. Thus, it is evident that the representation of the heat
capacity in the form of sum (1) is not complete and needs
some correction, namely, the introduction of excess δC(y,T)
contribution. Hence, in general case, the heat capacity of
Zn-doped LSCO samples above 3.5 K can be presented as
follows:
C(y,T) = γ(y)T + CS(y,T) + Cph(y,T) + δC(y,T) (4)
with δC(0,T) = 0.
Then, the difference in heat capacity between the
investigated sample La1.84Sr0.16Cu0.967Zn0.033O4 and the
reference sample La1.84Sr0.16Cu0.94Zn0.06O4 will have the
following form:
ΔC(y2,y1,T) – Δγ(y2,y1)T = δС(y2,T) – δС(y1,T) , (5)
y2 = 0.033 and y1 = 0.06 .
As Fig. 2 shows, in the normal phase (when y ≥ yc),
δC(y,T) has the form of a wide peak increasing almost
linearly and shifting to high temperatures with the increase
of zinc concentration. As δС(y1,T) is shifted to the higher
temperatures relative to δС(y2,T), on the plot in Fig. 2 we
have a valley according to Eq. (5). The experimentally
observed shift of the maximum of δC(y,T) value according
to the temperature with the increase of impurity concen-
tration is not characteristic of the anomalies of phonon part
of heat capacity of materials [11], just on the contrary, it is
in agreement with the magnetic nature of this contribution,
which is characterized by a large shift of the maximum ac-
cording to the temperature at the increase of impurity
concentration.
Taking into account the additional term in heat capa-
city, for ΔC – ΔγT value, from Eq. (4) we obtain the
following expression:
ΔC(0,y1,T) – Δγ(0,y1)T = CS(0,T) – δC(y1,T), (6)
which explains the reason of appearance of the negative
region on Fig. 1 (curve 1), and Eq. (3) will return to
ΔC(0,y1,T) – Δγ(0,y1)T + δC(y1,T) = CS(0,T). (7)
Figure 1, curve 2 (full circles), shows the dependence of
ΔC(0,y1,T) – Δγ(0,y1)T + δC(y1,T) on T, where the excess
contribution is δC(y1,T) = δC(0.033,T) [δC(0.033,T) is
taken from Fig. 2 (left peak)]. One can easily see that,
there is not an unphysical region for CS(0,T).
Conclusion
Summing up the above-said, one can conclude that in
LSCO ceramic superconductors at the introduction of Zn
in nonsuperconducting state there arises the anomaly of
low-temperature heat capacity giving evidence for the
existence of a new magnetic anomaly. The value of the
anomaly is shifted strongly towards high temperatures
and increases almost proportionally with the concentration
of Zn.
The authors express their very deep gratitude to
Prof. G. Kharadze for his interest to the article and useful
discussion of the above-given results.
The modification of PDC was supported by the INTAS
Grant N1010-CT93–0046.
Fig. 1. Heat capacity of superconducting electrons without (1)
and with (2) additional term δC.
0 5 10 15 20 25 30 35 40 45 50 55
–0.1
0
0.1
0.2
0.3
0.4
1
2
C
,
J/
(m
o
l·
K
)
S
T, K
Fig. 2. Temperature dependence of the ΔC–ΔγT for molar heat capa-
city between nonsuperconducting samples La1.84Sr0.16Cu0.967Zn0.033O4
and La1.84Sr0.16Cu0.94Zn0.06O4.
0 10 20 30 40 50
–0.10
–0.08
–0.06
–0.04
–0.02
0
0.02
0.04
0.06
0.08
�
�
�
C
T
,
J/
(m
o
l·
K
)
–
T, K
The evidence of a new magnetic anomaly in Zn-doped LSCO cuprates
Fizika Nizkikh Temperatur, 2010, v. 36, No. 3 271
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