Heat capacity studies of magnetic phase transition in sodium-rich NaxCoO₂ (0.73 ≤ x ≤ 0.87)

Specific heat measurements in the temperature region from 2 to 50 K in magnetic field up to 10 T, oriented parallel and perpendicularly to the CoO₂ layers were carried out on a series of high-quality single- crystals of NaxCoO₂ (x = 0.73, 0.76, 0.77, 0.78 and 0.87). Surprisingly, sharp lambda type a...

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Datum:	2009
Hauptverfasser:	Baran, A., Botko, M., Zorkovská, A., Kajňaková, M., Šebek, J., Šantavá, E., Peng, J.P., Lin, C.T., Feher, A.
Format:	Artikel
Sprache:	English
Veröffentlicht:	Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України 2009
Schriftenreihe:	Физика низких температур
Schlagworte:	Низкотемпеpатуpный магнетизм
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Zitieren:	Heat capacity studies of magnetic phase transition in sodium-rich NaxCoO₂ (0.73 ≤ x ≤ 0.87) / A. Baran, M. Botko, A. Zorkovská, M. Kajňaková, J.Šebek, E. Šantavá, J.P. Peng, C.T. Lin, A. Feher // Физика низких температур. — 2009. — Т. 35, № 10. — С. 1030-1033. — Бібліогр.: 29 назв. — англ.

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spelling	nasplib_isofts_kiev_ua-123456789-1174132025-06-03T16:26:44Z Heat capacity studies of magnetic phase transition in sodium-rich NaxCoO₂ (0.73 ≤ x ≤ 0.87) Baran, A. Botko, M. Zorkovská, A. Kajňaková, M. Šebek, J. Šantavá, E. Peng, J.P. Lin, C.T. Feher, A. Низкотемпеpатуpный магнетизм Specific heat measurements in the temperature region from 2 to 50 K in magnetic field up to 10 T, oriented parallel and perpendicularly to the CoO₂ layers were carried out on a series of high-quality single- crystals of NaxCoO₂ (x = 0.73, 0.76, 0.77, 0.78 and 0.87). Surprisingly, sharp lambda type anomaly was observed only for the concentration x = 0.76 at temperature (21.80 ± 0.02) K, for all the remaining doping levels round anomaly in experimental data was visible at temperature ~ 20 K, indicating a smeared magnetic phase transition. While the magnetic field oriented perpendicularly to the CoO₂ layers shifts the temperature of this anomaly to lower values, parallel magnetic field has no influence on it, what indirectly supports the idea of A-type antiferromagnetic ordering in studied systems. This work was supported by the grants of Slovak Research and Development Agency under the contracts No. APVV-VVCE-0058-07 and No. APVV-0006-07, VEGA 1/0159/9, the NSF-0701400 project and the Slovak–Serbian bilateral project SK-SRB-01006 and AVOZ 10100520. 2009 Article Heat capacity studies of magnetic phase transition in sodium-rich NaxCoO₂ (0.73 ≤ x ≤ 0.87) / A. Baran, M. Botko, A. Zorkovská, M. Kajňaková, J.Šebek, E. Šantavá, J.P. Peng, C.T. Lin, A. Feher // Физика низких температур. — 2009. — Т. 35, № 10. — С. 1030-1033. — Бібліогр.: 29 назв. — англ. 0132-6414 PACS: 75.30.Kz, 71.27.+a, 75.40.Cx https://nasplib.isofts.kiev.ua/handle/123456789/117413 en Физика низких температур application/pdf Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
institution	Digital Library of Periodicals of National Academy of Sciences of Ukraine
collection	DSpace DC
language	English
topic	Низкотемпеpатуpный магнетизм Низкотемпеpатуpный магнетизм
spellingShingle	Низкотемпеpатуpный магнетизм Низкотемпеpатуpный магнетизм Baran, A. Botko, M. Zorkovská, A. Kajňaková, M. Šebek, J. Šantavá, E. Peng, J.P. Lin, C.T. Feher, A. Heat capacity studies of magnetic phase transition in sodium-rich NaxCoO₂ (0.73 ≤ x ≤ 0.87) Физика низких температур
description	Specific heat measurements in the temperature region from 2 to 50 K in magnetic field up to 10 T, oriented parallel and perpendicularly to the CoO₂ layers were carried out on a series of high-quality single- crystals of NaxCoO₂ (x = 0.73, 0.76, 0.77, 0.78 and 0.87). Surprisingly, sharp lambda type anomaly was observed only for the concentration x = 0.76 at temperature (21.80 ± 0.02) K, for all the remaining doping levels round anomaly in experimental data was visible at temperature ~ 20 K, indicating a smeared magnetic phase transition. While the magnetic field oriented perpendicularly to the CoO₂ layers shifts the temperature of this anomaly to lower values, parallel magnetic field has no influence on it, what indirectly supports the idea of A-type antiferromagnetic ordering in studied systems.
format	Article
author	Baran, A. Botko, M. Zorkovská, A. Kajňaková, M. Šebek, J. Šantavá, E. Peng, J.P. Lin, C.T. Feher, A.
author_facet	Baran, A. Botko, M. Zorkovská, A. Kajňaková, M. Šebek, J. Šantavá, E. Peng, J.P. Lin, C.T. Feher, A.
author_sort	Baran, A.
title	Heat capacity studies of magnetic phase transition in sodium-rich NaxCoO₂ (0.73 ≤ x ≤ 0.87)
title_short	Heat capacity studies of magnetic phase transition in sodium-rich NaxCoO₂ (0.73 ≤ x ≤ 0.87)
title_full	Heat capacity studies of magnetic phase transition in sodium-rich NaxCoO₂ (0.73 ≤ x ≤ 0.87)
title_fullStr	Heat capacity studies of magnetic phase transition in sodium-rich NaxCoO₂ (0.73 ≤ x ≤ 0.87)
title_full_unstemmed	Heat capacity studies of magnetic phase transition in sodium-rich NaxCoO₂ (0.73 ≤ x ≤ 0.87)
title_sort	heat capacity studies of magnetic phase transition in sodium-rich naxcoo₂ (0.73 ≤ x ≤ 0.87)
publisher	Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України
publishDate	2009
topic_facet	Низкотемпеpатуpный магнетизм
url	https://nasplib.isofts.kiev.ua/handle/123456789/117413
citation_txt	Heat capacity studies of magnetic phase transition in sodium-rich NaxCoO₂ (0.73 ≤ x ≤ 0.87) / A. Baran, M. Botko, A. Zorkovská, M. Kajňaková, J.Šebek, E. Šantavá, J.P. Peng, C.T. Lin, A. Feher // Физика низких температур. — 2009. — Т. 35, № 10. — С. 1030-1033. — Бібліогр.: 29 назв. — англ.
series	Физика низких температур
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first_indexed	2025-11-25T06:38:33Z
last_indexed	2025-11-25T06:38:33Z
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fulltext	Fizika Nizkikh Temperatur, 2009, v. 35, No. 10, p. 1030–1033 Heat capacity studies of magnetic phase transition in sodium-rich Na x CoO2 (0.73 � x � 0.87) A. Baran1, M. Botko1, A. Zorkovská1, M. Kajòaková1, J. Šebek2, E. Šantavá2, J.P. Peng3, C.T. Lin3, and A. Feher1 1 Centre of Low Temperature Physics of the Faculty of Science UPJŠ & Institute of Experimental Physics SAS 9 Park Angelinum, Košice 04154, Slovakia E-mail: alexander.feher@upjs.sk 2 Institute of Physics AS CR, Prague 18221, Czech Republic 3 Max-Planck-Institute for Solid State Research, 1 Heisenbergstr, Stuttgart D-70569, Germany Received April 9, 2009 Specific heat measurements in the temperature region from 2 to 50 K in magnetic field up to 10 T, ori- ented parallel and perpendicularly to the CoO2 layers were carried out on a series of high-quality sin- gle-crystals of NaxCoO2 (x = 0.73, 0.76, 0.77, 0.78 and 0.87). Surprisingly, sharp lambda type anomaly was observed only for the concentration x = 0.76 at temperature (21.80 ± 0.02) K, for all the remaining doping levels round anomaly in experimental data was visible at temperature ~ 20 K, indicating a smeared magnetic phase transition. While the magnetic field oriented perpendicularly to the CoO2 layers shifts the temperature of this anomaly to lower values, parallel magnetic field has no influence on it, what indirectly supports the idea of A-type antiferromagnetic ordering in studied systems. PACS: 75.30.Kz Magnetic phase boundaries (including magnetic transitions, metamagnetism, etc.); 71.27.+a Strongly correlated electron systems; heavy fermions; 75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical expo- nents, etc.). Keywords: cobaltates, specific heat, magnetic phase transition, A-type antiferromagnetism. Introduction Transition metal oxide NaxCoO2 is a subject of intense study for its unusually high thermoelectric power [1], for the discovery of superconduct iv i ty in hydrated Na0.3CoO2 [2] and for very rich phase diagram with vari- ous electronic and magnetic ground states as a function of x. It is a paramagnetic metal at x ~ 0.3, a charge-ordered insulator at x = 0.5 and then a «Curie–Weiss metal» at x ~ 0.7 [3] with unconvential electronic behavior [4–6]. For x in the range 0.75–0.9 a magnetic transition with TN between 19 and 27 K was observed [7–10]. Recent neutron scattering studies of Na0.75CoO2, Na0.82CoO2, and Na0.85CoO2 have established that the magnetic order and dynamics are consistent with an A-type antiferromagnetic structure, in which a ferromag- netic interaction was revealed within the CoO2 layers and the layers themselves interact antiferromagnetically [11–13]. Moreover, the latest studies of correlation ef- fects via cellular clusters by means of the rotationally invariant slave boson method provide a theoretical sup- port for intralayer ferromagnetic order in highly doped NaxCoO2 [14]. Specific heat studies confirm the antiferromagnetic phase transition at 22 K [8,15,16], and recently a further ferromagnetic phase transition was observed at 8 K in Na0.85CoO2 [17]. This transition the authors clearly con- nect to the rearrangement of sodium ions at around 200 K, which leads to a phase separation. Despite a lot of experimental and theoretical work concerning the study of NaxCoO2, many questions about the magnetic state of cobaltates are still unresolved, be- sides the A-type antiferromagnetic ordering [15] also a spin-density-wave scenario is considered [16,20], or the coexistence of this two types of magnetically ordered state is assumed [8]. © A. Baran, M. Botko, A. Zorkovská, M. Kajòaková, J. Šebek, E. Šantavá 2, J.P. Peng3, C.T. Lin3, and A. Feher1, 2009 In the present paper we investigate the specific heat of sodium-rich NaxCoO2 and the influence of the orientation of magnetic field on the phase transition. We observed a round anomaly corresponding to the phase transition for all samples except the x = 0.76 concentration having a lambda type anomaly, in this respect the influence of the cluster character on the phase transition is discussed. The observed effect of magnetic field oriented parallel and perpendicularly to the CoO2 planes on the phase transi- tion is in agreement with the A-type antiferromagnetic or- dering. Experimental High quality single-crystal samples of NaxCoO2 with x = 0.73, 0.76, 0.77, 0.78 and 0.87 were grown in an opti- cal floating zone furnace with four 300 W halogen lamps installed as infrared radiation sources. Starting feed and seed materials were prepared from Na2Co3 and Co3O4 of 99.9% purity with the nominal composition of NaxCoO2. To ensure homogeneous and pure phase all the process procedures were carefully controlled and examined using x-ray diffraction. The composition of the as-grown crys- tals were determined by energy dispersive x-ray analysis (EDX), the sodium composition distribution was homo- geneous with error less up to 2 at.%. The growth details are described in Refs. 18, 19. Specific heat of samples in magnetic field up to 10 T oriented parallel and perpendicularly to the ab (CoO2) plane has been measured in the temperature range from 2 to 50 K using the conventional Quantum Design PPMS-14 equipment. Because the recent experimental works [17] pointed to possible changes of sample proper- ties by cooling procedure, we used the same cooling rates for all samples to ensure the identical conditions for spe- cific heat measurements. Results and discussion The specific heat data for single-crystals in magnetic field of 0, 9 and 10 T for both orientation of field, i.e., per- pendicularly and parallel to the ab plane, are shown in Figs. 1,a and b. As we can see, relatively sharp lambda type anomaly is visible at (21.80 ± 0.02) K for concentra- tion x = 0.76, while for other concentrations smeared anomalies in specific heat can be observed around 20 K. The differences are better visible on Fig. 2, after subtrac- tion of the lattice contribution to specific heat, fitted nu- merically. The lambda type anomaly indicates magnetic ordering, consistent with previous experimental results, showing similar phase transition in specific heat at about 22 K [8,16,20]. The origin of the broad anomaly at ~ 20 K might be attributed to the cluster character of the system, ordering in the clusters can smear the transition. This is in agreement with the previous evidence of the intrinsically Heat capacity studies of magnetic phase transition in sodium-rich NaxCoO2 Fizika Nizkikh Temperatur, 2009, v. 35, No. 10 1031 4.0 3.5 3.0 3.0 2.5 2.5 2.0 2.0 1.5 1.5 1.0 1.0 0.5 17 18 18 19 19 20 20 21 21 22 22 23 23 24 T, K T, K C ,J /( m ol ·K ) C ,J /( m ol ·K ) 9 T, x = 0.73 10 T, x = 0.73 10 T, x = 0.76 10 T, x = 0.78 9 T, x = 0.77 10 T, x = 0.78 10 T, x = 0.87 B ab plane� B \|\| ab plane 0 T 0 T 0 T 0 T 0 T 0 T 0 T a b Fig. 1. Specific heat of NaxCoO2 for various concentrations x. Magnetic field oriented perpendicularly to the ab plane (a). Specific heat of NaxCoO2 for selected concentrations. Mag- netic field oriented parallel to the ab plane (b). C /T ,J /( m ol ·K 2 ) x = 0.73 x = 0.76 x = 0.77 x = 0.78 x = 0.87 0.025 0.020 0.015 0.010 0.005 0 50 70 46 37 35 S , mJ/(mol·K)mag 14 16 18 20 22 24 T, K Fig. 2. Comparison of the phase transition anomaly and the in- volved entropy for different Na doping. inhomogeneous magnetic state related to the Na doping [21]. Even though there are strong indications (EPR and NMR measurements [22], neutron scattering results [23,24] and STM investigations [25]) that this inhomo- geneity is of mesoscopic scale, the observed coexistence of two magnetic phases, ordering at different tempera- tures [17], represents an example when the system is mac- roscopically phase separated. Thus, the intense debate about the character of inhomogeneities in cobaltates has still not come to the end. The cluster structure originates from several compet- ing effects in the system, the impact of which changes upon doping. Geometric frustration of antiferromagnetic interactions on triangular lattice is gradually lifted by Na addition, consequently, there must exist a critical doping at which frustration ceases and the system orders. Recent Monte Carlo study tracks the smearing influence of geo- metric frustration on specific heat [26]. On the other hand, Na doping leads to magnetic dilution of the system, which can smear the transition again. In terms of the above reasoning, the concentration x = 0.76 might repre- sent a critical doping, at which the percolating cluster structure can develop a long range magnetic order; even- tually at which the long range Na superstructure forma- tion, which is observed on 3/4 doped Na0.75CoO2 sam- ples by high energy x-ray diffraction [27] can promote the long range magnetic ordering as well. According to Fig. 2, the entropy involved in the magnetic phase transi- tion for all samples is very small, it has maximum obvi- ously at doping x = 0.76, but even in this case it reaches only ~ 0.07 J/(mol·K). If magnetic phase transition corre- sponded to the long range magnetic ordering of localized Co+4 spins, we would expect the entropy associated with the transition to be of order 0.24R ln 2 ~ 1.38 J /(mol·K). This value is 20 times larger than entropy found experi- mentally and supports the idea about unconventional magnetic ordering, such as spin density wave [16,28]. The magnetic field applied perpendicular to the ab plane shifts the magnetic phase transition towards lower temperatures (Fig. 1,a). On the other hand, magnetic field oriented parallel to the ab planes has no influence on spe- cific heat, as it can be seen from Fig. 1,b. The fact that the specific heat anomaly about 20 K is sensitive only to the magnetic field oriented perpendicularly to the CoO2 lay- ers is in accordance with the picture, in which the mag- netic moments within the CoO2 layers point out of layers and are likely ferromagnetically coupled, while the interlayer interactions are antiferromagnetic. Detailed study of the influence of perpendicular mag- netic field between 0 and 9 T on the specific heat of sin- gle-crystal Na0.77CoO2 is illustrated in Fig. 3. In mag- netic fields from 0 to 3 T no significant influence on specific heat is visible, the dependences are almost identi- cal. As the magnetic field is increased from 3 to 9 T, the phase transition critical temperature TN, estimated as a peak temperature of the anomaly, gradually shifts to lower values. Similar tendency was observed in specific heat study under magnetic field up to 14 T applied per- pendicularly to the ab plane, with metamagnetic phase transition at 8 T [29]. Inset of Fig. 3 shows the phase dia- gram of the sample Na0.77CoO2. By extrapolation to zero temperature we guessed very roughly the saturation mag- netic field as ~ 133 T ~ 7.7 meV, which gives idea about the strength of interlayer interactions. These values are quite reasonable, not far from that estimated by neutron scattering [15]. Conclusion We have measured the specific heat of sodium-rich single crystals of NaxCoO2, with attention to the in- fluence of Na doping on the magnetic phase transition. Surprisingly, sharp lambda type anomaly was observ- ed only for the concentration x = 0.76 at temperature (21.80 ± 0.02) K, for all the remaining doping levels both below and above x = 0.76 round anomaly in experimen- tal data was visible at temperature ~ 20 K, indicating a smeared magnetic phase transition, likely as a conse- quence of competing magnetic frustration and dilution ef- fects. The influence of the cluster character on the phase transition was discussed. The influence of magnetic field, applied parallel and perpendicularly to ab plane, indi- rectly supports the A-type ferromagnetism. Acknowledgment This work was supported by the grants of Slovak Research and Development Agency under the contracts 1032 Fizika Nizkikh Temperatur, 2009, v. 35, No. 10 A. Baran et al. 0 T 1 T 2 T 3 T 4 T 5 T 6 T 7.5 T 9 T C ,J /( m ol ·K ) 2.7 2.6 2.5 2.4 2.3 2.2 18.5 19.0 19.5 20.0 20.5 21.0 T, K 19.2 19.6 20.0 10 8 6 4 2 0 B ,T T , KN Fig. 3. Influence of perpendicular magnetic field up to 9 T on specific heat of Na0.77CoO2. Inset: Phase diagram for single crystal Na0.77CoO2 . No. APVV-VVCE-0058-07 and No. APVV-0006-07, VEGA 1/0159/9, the NSF-0701400 project and the Slovak–Serbian bilateral project SK-SRB-01006 and AVOZ 10100520. 1. Y. Wang, N.S. Rogado, R.J. Cava, and N.P. Ong, Nature (London) 423, 425 (2003). 2. K. Takada, H. Sakurai, E. Takayama-Muromachi, F. Izu- mi, R.A. Dilanian, and T. Sasaki, Nature (London) 422, 53 (2003). 3. M.L. Foo, Y. Wang, S. Watauchi, H.W. Zandbergen, T. He, R.J. Cava, and N.P. Ong, Phys. Rev. Lett. 92, 247001 (2004). 4. L. Balicas, Y.J. Jo, G.J. Shu, F.C. Chou, and P.A. Lee, Phys. Rev. Lett. 100, 126405 (2008). 5. M. Brühwiler, B. Batlogg, S.M. Kazakov, Ch. Nieder- mayer, and J. Karpinski, Physica B378–380, 630 (2006). 6. A. Zorkovská, J. Šebek, E. Šantavá, I. Bradariæ, and A. Fe- her, Fiz. Nizk. Temp. 33, 1243 (2007) [Low. Temp. Phys. 33, 944 (2007)]. 7. J. Sugiyama, H. Itahara, J.H. Brewer, E.J. Ansaldo, T. Mo- tohashi, M. Karppinen, and H. Yamauchi, Phys. Rev. B67, 214420 (2003). 8. T. Motohashi, R. Ueda, E. Naujalis, T. Tojo, I. Terasaki, T. Atake, M. Karppinen, and H. Yamauchi, Phys. Rev. B67, 064406 (2003). 9. P. Mendels, D. Bono, J. Bobroff, G. Collin, D. Colson, N. Blanchard, H. Alloul, I. Mukhamedshin, F. Bert, A. Ama- to, and A.D. Hillier, Phys. Rev. Lett. 94, 136403 (2005). 10. J. Sugiyama, J.H. Brewer, E.J. Ansaldo, B. Hitti, M. Mi- kami, Y. Mori, and T. Sasaki, Phys. Rev. B69, 214423 (2004). 11. A.T. Boothroyd, R. Coldea, D.A. Tennant, D. Prabhakaran, L.M. Helme, and C.D. Frost, Phys. Rev. Lett. 92, 197201 (2004). 12. L.M. Helme, A.T. Boothroyd, R. Coldea, D. Prabhakaran, D.A. Tennant, A. Hiess, and J. Kulda, Phys. Rev. Lett. 94, 157206 (2005). 13. S.P. Bayrakci, I. Mirebeau, P. Bourges, Y. Sidis, M. En- derle, J. Mesot, D.P. Chen, C.T. Lin, and B. Keimer, Phys. Rev. Lett. 94, 157205 (2005). 14. F. Lechermann, Phys. Rev. Lett. 102, 046403 (2009). 15. S.P. Bayrakci, C. Bernhand, D.P. Chen, B. Keimer, R.K. Kremer, P. Lemmens, C.T. Lin, C. Niedermayer, and J. Strempfer, Phys. Rev. B69, 100410(R) (2004). 16. J. Wooldridge, D. Paul, G. Balakrishman, and M. Lees, J. Phys.: Condens. Matter 17, 707 (2005). 17. T.F. Schulze, P.S. H�fliger, Ch. Niedermayer, K. Matten- berger, S. Bubenhofer, and B. Batlogg, Phys. Rev. Lett. 100, 026407 (2008). 18. D.P. Chen, H.C. Chen, A. Maljuk, A. Kulakov, H. Zhang, P. Lemmens, and C.T. Lin, Phys. Rev. B70, 024506 (2004). 19. J.B. Peng and C.T. Lin, J. Crystal Growth 311, 921 (2009). 20. B.C. Sales, R. Jin, K.A. Affholter, P. Khalifah, G.M. Veith, and D. Mandrus, Phys. Rev. B70, 174419 (2004). 21. C. Bernhard, Ch. Niedermayer, A. Drew, G. Khaliullin, S. Bayrakci, J. Stempfer, R.K. Kremer, D.P. Chen, C.T. Lin, and B. Keimer, Europhys. Lett. 80, 27005 (2007). 22. P. Carretta, M. Mariani, C.B. Azzoni and M.C. Mozzati, I. Bradariæ, I. Saviæ, A. Feher, J. Šebek, Phys. Rev. B70, 024409 (2004). 23. M. Roger, D.J.P. Morris, D.A. Tennant, M.J. Gutmann, J.P. Goff, J.-U. Hoffmann, R. Feyerherm, E. Dudzik, D. Prabhakaran, A.T. Boothroyd, N. Shannon, B. Lake, and P.P. Deen, Nature 445, 631 (2007). 24. D.J.P. Morris, M. Roger, M.J. Gutmann, J.P. Goff, D.A. Tennant, D. Prabhakaran, A.T. Boothroyd, E. Dud- zik, R. Feyerherm, J.-U. Hoffmann, and K. Kiefer, arXiv:0803.1312v2. 25. W.W. Pai, S.H. Huang, Y.S. Meng, Y.C. Chao, C.H. Lin, H.L. Liu, and F.C. Chou, Phys. Rev. Lett. 100, 206404 (2008). 26. A. Mañka-Krasoñ and K. Kulakowski, cond-mat/0812.1128v1. 27. J. Geck, M. Zimmermann, H. Berger, S.V. Borisenko, H. Eschrig, K. Koepernik, M. Knupfer, and B. Büchner, Phys. Rev. Lett. 97, 106403 (2006). 28. B.C. Sales, R. Jin, K.A. Affholter, P. Khalifah, G.M. Veith, and D. Mandrus, Phys. Rev. B70, 174419 (2004). 29. J.L. Luo, N.L.Wang, G.T. Liu, D.Wu, X.N. Jing, F. Hu, and T. Xiang, Phys. Rev. Lett. 93, 187203 (2004). Heat capacity studies of magnetic phase transition in sodium-rich NaxCoO2 Fizika Nizkikh Temperatur, 2009, v. 35, No. 10 1033

Heat capacity studies of magnetic phase transition in sodium-rich NaxCoO₂ (0.73 ≤ x ≤ 0.87)

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