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Thermodynamic properties of LSCO Cuprates in the Nonsuperconducting State
4. Nemsadze G., Leshava T., Gorgoshidze M., Kiladze M., Gogelia N., Khachidze D., Lomidze E., Monaselidze J. Blood plasma main proteins stability of patients with ductal carcinoma in post surgery period, Int. J. Clin. Exp. Med. - 1338-1345, 9 (2), - 2016.
5. Hadareishvili M., Kiziria E., Sokhadze V., Tvauri G., The problem of high heating rate in differential calorimetry, Proceedings of the 13th European conference on innovations and Natural Sciences, - P. 112-117, - Vienna 2017. "East West" Association for Advanced Studies and Higher Education GmbH.
6. Nadareishvili M. M. and Kvavadze K. A., The Evidence of a New Magnetic Anomaly in Zn-doped LSCO Cuprates, Low Temperature Physics, - Vol. 36, - N3, - P. 210, - 2010.
DOI: http://dx.doi.org/10.20534/ESR-17-1.2-255-256
Nadareishvili Malkhaz, Tbilisi State University, Institute of Physics, senior researcher E-mail: malkhaz.nadareishvili@tsu.ge Kiziria Evgeni, Tbilisi State University, Institute of Physics, Leading researcher E-mail: evgenikiziria@hotmail.com Sokhadze Viktor, Tbilisi State University Institute of Physics, senior researcher E-mail: vsokhadze@yahoo.com Tvauri Genadi, Tbilisi State University Institute of Physics, Engineer E-mail: gena-tvauri@yahoo.com Tsakadze Severian, Tbilisi State University, Institute of Physics, senior researcher E-mail: ztsakadze@gmail.com
Thermodynamic properties of LSCO Cuprates in the Nonsuperconducting State
Abstract: The investigations of low-temperature heat capacity in pure (y=0) and Zn-doped Lax 84Sr016Cux-yZnyO4 samples (y=0.033 and 0.06) have been performed by high-precision differential pulsed calorimeter (DPC) measuring the heat capacities under the thermodinamicaly equilibrium conditions in contrast to the commonly used differential scanning calorimeters (DSC). The anomaly of a low-temperature heat capacity which has a wide peak form and is related with Zn impurity was observed in the nonsuperconducting state in agreement with the neutron scattering experiments. The shape of anomaly indicates that Zn-induced magnetic ordering transition is of the first order transition type in the investigated cases. The anomaly shifts to higher temperatures with the increase of Zn content as it is characteristic of the anomalies of magnetic nature in contrast to anomalies of phonon heat capacity.
Keywords: Calorimeter, differential calorimeter, High temperature Superconductors, Superconducting Cuprates.
Introduction
There exists the suggestion that the dynamic spin correlations (spin fluctuations) should play an important role in the mechanism of high-temperature superconductivity [1; 2]. To clarify the situation in this direction, the influence of magnetic and nonmagnetic impurities in the high-temperature superconducting cuprates La2xSrxCuO4 (LSCO) have been intensively studied [3].
The neutron scattering experiments [4] show that in monocrys-talline La179Sr021Cu099Zn001O4 sample in the non superconducting state there appear the elastic peaks indicating that Zn influences on AF dynamic spin correlations and stabilizes them into the static ones.
In the ^SR investigations of Zn-dopd LSCO [5] it was also observed that the AF magnetic order appears in La^SrCuj yZnyO4
samples in non superconducting state at x=0.21 and y=0.01. The thermodynamic investigations of Zn-doped LSCO cuprates were carried out both with the usual pulsed calorimetric technique measuring the absolute heat capacity of samples [6], and with the differential scanning calorimetry (DSC) measuring the heat capacity difference between the investigated and the reference samples [7], however, the data of thermodynamic characteristics of this phenomenon are not available. The cause in our opinion is not sufficient precision of used techniques.
Results and Discussion
We made the measurements of low temperature heat capacity in pure and Zn-doped LSCO samples by the original, created with us, differential pulsed calorimeter (DPC) with high precision
Section 14. Physics
[8], a brief description of the first, imperfect experimental version of which was given earlier [9]
Figure 1 clearly shows a wide maximum of the heat capacity as required by neutron scattering experiments.
0,10* 0,08 1 0,060,04-
0,02-
0,00
80
90
100 T K
110
120
Figurel. The anomaly of the heat capacity appropriate to the concentration of zinc; - y = 0.033
^ 0,08-,
0,04-1 0,00 -0,04-1 -0,08
80 90 100 110 120 130 140 T K
Figure 2 The difference of the heat capacities between
the samp|es La184Sro,6Cuo.967Zno.o3304 and
Lai.84Sr0.16CU0.94Zn0.06O4
To determine the concentration dependence of the effect we measured the heat capacity difference AC (y2, y1, T) between two non-superconducting samples La184Sr016Cu1-yZnjO4, with different content of Zn (y2=0.033 and y1=0.06). Fig.2 shows that this dependence is of a complex form AC (y2, y1, T) = SC (y2, T) — SC (y1, T), where each SC (y, T) has the form of a wide peak.
This means that in Zn-doped LSCO cuprates there appears the anomaly of heat capacity SC (y, T), having the form of a wide peake. As SC (y1, T) peak is shifted to the high temperatures relative to SC (y2, T) peak, on the plot of Fig.2 there appears a sinusoidal like curve. The experimentally observed shift of the maximum of SC (y, T) along the temperature with the increase of impurity concentration is not characteristic of the anomalies of a phonon part of heat capacity of materials [10], just on the contrary, it is related with the magnetic nature of this contribution in agreement with the neutron scattering experiments.
Conclusion
Summing up the above-said, one can conclude that in LSCO ceramic superconductors, at the introduction of Zn in nonsupecon-ducting state, the anomaly of low-temperature heat capacity related with Zn-induced static spin correlations was observed in agreement with the neutron scattering experiments. The shape of anomaly indicates that Zn-induced magnetic ordering transition to the static spin correlation is of the first order transition type in our investigated cases. The value of this anommaly at the investigated concentrations increases almost proportionally to Zn concentration and shifts to higher temperatures with the increase of Zn content, as it is characteristic of the anomalies of magnetic nature, in contrast to the anomalies of phonon nature.
The work was supported by Rustavely Foundation Grant # FR/500/6-130/13
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