KCuF3 is a Mott-Hubbard insulator with a distorted perovskite structure (space group I4/mcm). The structural distortion is due to orbital ordering (OO) associated with cooperative Jahn-Teller effect (JT) [1]. and corresponds to an alternate occupation of Cu-3dy2-z2 and Cu-3dx2-z2 hole states on Cu(3d9) ion [2]. The orbital configuration results in quasi one-dimensional magnetic properties. Nearest-neighbour superexchange (NN-SE) interactions are strong and antiferromagnetic (AF) along the c axis and, for T>TN=38 K, weak and ferromagnetic in the ab plane. Debate is open in the literature on the actual driving force (i.e. either OO or JT) of the structural distortion and of the related electronic and magnetic properties. We have recently found experimental evidence of the ideal situation in which OO is melted while the JT distortion is still present:, in fact OO is expected to be very sensitive to slight changes in the electronic structure. Electron paramagnetic resonance investigations revealed melting of OO at room temperature in the KCu1-xMgxF3 system for x=0.1 [3]. We presents here a Synchrotron Radiation X-ray powder diffraction (XRPD) study in a sample with composition KCu0.8Mg0.2F3, which at room temperature is isostructural with KCuF3, a prototypical system for studying Orbital Order (OO). This sample can be considered a realisation of the ideal situation in which OO is melted while the cooperative JT distortion is still present. The melting of the cooperative JT distortion is observed in this system for T~600 K. This result is discussed in the framework of the different energy scales for OO and cooperative JT distortion. [1] L.F. Feiner, A.M. Oleś, J. Zaanen, Phys. Rev. Lett., 1997, 78, 2799. [2] R. Caciuffo, L. Paolasini, A. Sollier, P. Ghigna, E. Pavarini, J. van den Brink, M. Altarelli Phys.Rev., 2002, B65, 174425 [3] C. Oliva, M. Scavini, S. Cappelli, C. Bottalo, C. Mazzoli, P. Ghigna, J.Phys.Chem., 2007, B111, 5976
Melting of cooperative Jahn-Teller distortion in KMg0.2Cu0.8F3 / M. Scavini, M. Brunelli, P. Ghigna, C. Ferrero, C. Mazzoli. ((Intervento presentato al 15. convegno SILS national congress tenutosi a Milano nel 2007.
Melting of cooperative Jahn-Teller distortion in KMg0.2Cu0.8F3
M. ScaviniPrimo
;
2007
Abstract
KCuF3 is a Mott-Hubbard insulator with a distorted perovskite structure (space group I4/mcm). The structural distortion is due to orbital ordering (OO) associated with cooperative Jahn-Teller effect (JT) [1]. and corresponds to an alternate occupation of Cu-3dy2-z2 and Cu-3dx2-z2 hole states on Cu(3d9) ion [2]. The orbital configuration results in quasi one-dimensional magnetic properties. Nearest-neighbour superexchange (NN-SE) interactions are strong and antiferromagnetic (AF) along the c axis and, for T>TN=38 K, weak and ferromagnetic in the ab plane. Debate is open in the literature on the actual driving force (i.e. either OO or JT) of the structural distortion and of the related electronic and magnetic properties. We have recently found experimental evidence of the ideal situation in which OO is melted while the JT distortion is still present:, in fact OO is expected to be very sensitive to slight changes in the electronic structure. Electron paramagnetic resonance investigations revealed melting of OO at room temperature in the KCu1-xMgxF3 system for x=0.1 [3]. We presents here a Synchrotron Radiation X-ray powder diffraction (XRPD) study in a sample with composition KCu0.8Mg0.2F3, which at room temperature is isostructural with KCuF3, a prototypical system for studying Orbital Order (OO). This sample can be considered a realisation of the ideal situation in which OO is melted while the cooperative JT distortion is still present. The melting of the cooperative JT distortion is observed in this system for T~600 K. This result is discussed in the framework of the different energy scales for OO and cooperative JT distortion. [1] L.F. Feiner, A.M. Oleś, J. Zaanen, Phys. Rev. Lett., 1997, 78, 2799. [2] R. Caciuffo, L. Paolasini, A. Sollier, P. Ghigna, E. Pavarini, J. van den Brink, M. Altarelli Phys.Rev., 2002, B65, 174425 [3] C. Oliva, M. Scavini, S. Cappelli, C. Bottalo, C. Mazzoli, P. Ghigna, J.Phys.Chem., 2007, B111, 5976Pubblicazioni consigliate
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