1. Signatures of Berezinskii-Kosterlitz-Thouless transition in double-layered molecular magnet based on [W V (CN) 8 ] 3- and Cu 2+ Signatures of Berezinskii-Kosterlitz-Thouless transition in double-layered molecular magnet based on [W V (CN) 8 ] 3- and Cu 2+ Robert Pełka Department of Structure Research of Condensed Matter H. Niewodniczański Institute of Nuclear Physics Polish Academy of Sciences, Cracow, Poland

2. Publications Department of Structure Research of Condensed Matter 1)R. Podgajny, T. Korzeniak, M. Bałanda, T. Wasiutyński, W. Errington, T.J. Kemp, N.W. Alcock, B. Sieklucka, Chem. Commun. (2002) 1138. 2)T. Korzeniak, R. Podgajny, N.W. Alcock, K. Lewiński, M. Bałanda, T. Wasiutyński, B. Sieklucka, Polyhedron 22 (2003) 2183. 3)R. Pełka, M. Bałanda, T. Wasiutyński, Y. Nakazawa, M. Sorai, R. Podgajny, B. Sieklucka, Czech. J. Phys. 54 (2004) 595. 4)M. Bałanda, T. Korzeniak, R. Pełka, R. Podgajny, M. Rams, B. Sieklucka, T. Wasiutyński, Solid State Sci. 7 (2004) 1113. 5)F.L. Pratt, P.M. Zieliński, M. Bałanda, R. Podgajny, T. Wasiutyński, B. Sieklucka, J. Phys.: Condens. Matter 19 (2007) 456208. 6)M. Bałanda, R. Pełka, T. Wasiutyński, M. Rams, Y. Nakazawa, Y. Miyazaki, M. Sorai, R. Podgajny, T. Korzeniak, B. Sieklucka, Phys. Rev. B78 (2008) 174409.

3. Department of Structure Research of Condensed Matter  M. Bałanda, P.M. Zieliński, R.Pełka, T. Wasiutyński H. Niewodniczański Institute of Physics, Polish Academy of Sciences, Cracow, Poland  R. Podgajny, T. Korzeniak, B. Sieklucka Faculty of Chemistry, Jagiellonian University, Cracow, Poland  Y. Nakazawa, Y. Miyazaki, M. Sorai Research Center for Molecular Thermodynamics, Graduate School of Science, Osaka University  F. L. Pratt ISIS Facility, Rutherford Appleton Laboratory, Chilton, Oxfordshire, UK  M. Rams Institute of Physics, Jagiellonian University, Cracow, Poland

4. a new family of 2D coordination polymers showing magnetic properties Results engineering of cyano-bridged heterometallic coordination networks Methodology new molecular magnetsTarget Department of Structure Research of Condensed Matter

5. {(tetrenH 5 ) 0.8 Cu II 4 [W V (CN) 8 ] 4 7.2H 2 O} n CuC WN inter-bilayer distances W-W 9.6 Å Cu-W 11.2 Å orthorhombic space group: Cmc2 1 Department of Structure Research of Condensed Matter J intra ~ 80 K J inter /J intra ~ 10 -4

6. Magnetic and calorimetric measurements on powder samples have revealed magnetic phase transition at about 34 K Department of Structure Research of Condensed Matter

7. C lattice (T)=C p (T,H max ) C mag (T,H)=C p (T,H)- C p (T,H max ) Instrument: PPMS Quantum Design Field range: 0-90 kOe Calorimetry measurement a b c S max =R ln(2J+1) 8 =46.1 J/(K mol) with J=1/2 S(0 Oe)/S max ≈15% Department of Structure Research of Condensed Matter

8. Magnetic measurements strong easy-plane anisotropy metamagnetic behavior Department of Structure Research of Condensed Matter

9. Static scaling hypothesis R. Omari, J. J. Préjean, J. Souletie, J. Physique 44, 1983, 1069. J. Souletie, J. L. Tholence, Solid State Coummun. 48, 1983, 407. T c,ac,T c,b T 0,b 2D XY2D XXZ 1.82 1) 2.17 2) 1) R. Gupta et al., Phys. Rev. Lett. 61, 1988, 1996. 2) A. Cuccoli et al., Phys. Rev. B 52, 1995, 10221. Department of Structure Research of Condensed Matter

10. Berezinskii-Kosterlitz-Thouless transition The transition is driven by unbinding of vortex pairs. The correlation length ξ and the in-plane susceptibility  diverge exponentially The correlation functions of the fluctuations of the in-plane spin components decay exponentially above T BKT and with power law below T BKT. for ( at ) Department of Structure Research of Condensed Matter

12.  SR spectroscopy F.L. Pratt et al., J. Phys.:Condens. Matter 19 (2007) 456208 S.T. Bramwell, P.C.W. Holdsworth, Phys. Rev. 49 (1994) 8811 Temperature dependence of local fields B 1 and B 2 Department of Structure Research of Condensed Matter

13.  A unique quasi-2D molecular magnet was designed.  The entropy of magnetic transition amounts to only 15% of the maximal expected value, which indicates a well-established state of short-range order above the transition temperature.  There is strong easy-plane anisotropy in the system.  Metamagnetic behavior with critical field of 100 Oe.  The scaling analysis of the critical region indicates that the transition might be of the Berezinskii-Kosterlitz-Thouless type.  The exponent beta for the local fields found by μSR technique is as expected for the BKT transition. Conclusions Department of Structure Research of Condensed Matter

14. Thank you for your attention Department of Structure Research of Condensed Matter