Three different AC and DC experiments have been performed in untwinned YBCO to clarify the mechan... more Three different AC and DC experiments have been performed in untwinned YBCO to clarify the mechanism of vortex pinning. Pinning by surface irregularities is the only mechanism consistent with all experiments. This questions usual interpretation in terms of bulk collective pinning theories. In particular, the irreversibility line appears as the dissapearance of superficial critical current.
The dielectric constant of the Kagome staircase-like Co3V2O8 polycrystalline compound has been me... more The dielectric constant of the Kagome staircase-like Co3V2O8 polycrystalline compound has been measured as function of temperature and magnetic field up to 14T. It is found that the application of an external magnetic field suppresses the anomaly for the dielectric constant beyond 6.1K. Furthermore, its magnetic field dependence reveals a negative magnetocapacitance which is proportional to the magnetic susceptibility, suggesting a common magnetostrictive origin for the magnetic field dependence of the two quantities. This result is very different from that obtained from the isostructural compound Ni3V2O8 that presents a peak in the dielectric constant at the incommensurate magnetic phase transition coupled to a sign change of the magnetocapacitance.
Columnar defects can be introduced in high Tc superconductors by irradiation with high energy hea... more Columnar defects can be introduced in high Tc superconductors by irradiation with high energy heavy ions. The concentration of these artificial pinning centers with a well characterized morphology is easily controlled. The pinning efficiency of these defects has been often demonstrated, mainly from magnetization measurements. In the present work, measure- ments of the electrical resistance along the c axis, Rc(T),
We have studied the vortex line correlations by a measurement of the electric field direction in ... more We have studied the vortex line correlations by a measurement of the electric field direction in a geometry of tilted vortices in a YBa2Cu3O7 crystal. At a given magnetic field, there are two different regimes: at low temperature, the vortices are fully correlated along their axis. ...
We report here the discovery of multiferroicity and large magnetoelectric coupling in the type I ... more We report here the discovery of multiferroicity and large magnetoelectric coupling in the type I orbital order system GeV₄S₈. Our study demonstrates that this clustered compound displays a para-ferroelectric transition at 32 K. This transition originates from an orbital ordering which reorganizes the charge within the transition metal clusters. Below the antiferromagnetic transition at 17 K, the application of a magnetic field significantly affects the ferroelectric polarization, revealing thus a large magnetoelectric coupling. Our study suggests that the application of a magnetic field induces a metamagnetic transition which significantly affects the ferroelectric polarization thanks to an exchange striction phenomenon.
... Lett. 90, 197201 (2003). GC Milward, MJ Calderon, and PB Littlewood, Nature (London) 433, 607... more ... Lett. 90, 197201 (2003). GC Milward, MJ Calderon, and PB Littlewood, Nature (London) 433, 607 (2005). J. Burgy, A. Moreo, and E. Dagotto, Phys. Rev. ... 93, 217402 (2004). S. Mercone, V. Hardy, C. Martin, Ch. Simon, D. Saurel and Annie Brûlet, Phys. Rev. B 68, 094422 (2003). ...
... Measurements for the triangular Ising-like cobaltite Ca 3 Co 2 O 6 have been made. Single cry... more ... Measurements for the triangular Ising-like cobaltite Ca 3 Co 2 O 6 have been made. Single crystals of Ca 3 Co 2 O 6 are found to exhibit a magnetodielectric effect below T N =25 K with a peak in the ε(H) curve at the ferri to ferromagnetic transition. ...
The slight incommensurate modulation of the structure of Bi(2)Mn(4/3)Ni(2/3)O(6) is sufficient to... more The slight incommensurate modulation of the structure of Bi(2)Mn(4/3)Ni(2/3)O(6) is sufficient to suppress the electrical polarization which arises in commensurate treatments of the structure, due to antiferroelectric coupling of local polar units of over 900 A(3). The incommensurate structure is produced by the competition between ferroelectric Bi lone pair-driven A site displacement, chemical order of Mn and Ni on the B site, and both charge and orbital order at these transition metals. The interplay between the frustrated polar Bi displacements and the frustrated spin order at the B site, induced by positional disorder, produces magnetodielectric coupling between the incommensurately modulated lattice and the spin-glass-like ground state with an unusual relationship between the magnetocapacitance and the applied field.
Three different AC and DC experiments have been performed in untwinned YBCO to clarify the mechan... more Three different AC and DC experiments have been performed in untwinned YBCO to clarify the mechanism of vortex pinning. Pinning by surface irregularities is the only mechanism consistent with all experiments. This questions usual interpretation in terms of bulk collective pinning theories. In particular, the irreversibility line appears as the dissapearance of superficial critical current.
The dielectric constant of the Kagome staircase-like Co3V2O8 polycrystalline compound has been me... more The dielectric constant of the Kagome staircase-like Co3V2O8 polycrystalline compound has been measured as function of temperature and magnetic field up to 14T. It is found that the application of an external magnetic field suppresses the anomaly for the dielectric constant beyond 6.1K. Furthermore, its magnetic field dependence reveals a negative magnetocapacitance which is proportional to the magnetic susceptibility, suggesting a common magnetostrictive origin for the magnetic field dependence of the two quantities. This result is very different from that obtained from the isostructural compound Ni3V2O8 that presents a peak in the dielectric constant at the incommensurate magnetic phase transition coupled to a sign change of the magnetocapacitance.
Columnar defects can be introduced in high Tc superconductors by irradiation with high energy hea... more Columnar defects can be introduced in high Tc superconductors by irradiation with high energy heavy ions. The concentration of these artificial pinning centers with a well characterized morphology is easily controlled. The pinning efficiency of these defects has been often demonstrated, mainly from magnetization measurements. In the present work, measure- ments of the electrical resistance along the c axis, Rc(T),
We have studied the vortex line correlations by a measurement of the electric field direction in ... more We have studied the vortex line correlations by a measurement of the electric field direction in a geometry of tilted vortices in a YBa2Cu3O7 crystal. At a given magnetic field, there are two different regimes: at low temperature, the vortices are fully correlated along their axis. ...
We report here the discovery of multiferroicity and large magnetoelectric coupling in the type I ... more We report here the discovery of multiferroicity and large magnetoelectric coupling in the type I orbital order system GeV₄S₈. Our study demonstrates that this clustered compound displays a para-ferroelectric transition at 32 K. This transition originates from an orbital ordering which reorganizes the charge within the transition metal clusters. Below the antiferromagnetic transition at 17 K, the application of a magnetic field significantly affects the ferroelectric polarization, revealing thus a large magnetoelectric coupling. Our study suggests that the application of a magnetic field induces a metamagnetic transition which significantly affects the ferroelectric polarization thanks to an exchange striction phenomenon.
... Lett. 90, 197201 (2003). GC Milward, MJ Calderon, and PB Littlewood, Nature (London) 433, 607... more ... Lett. 90, 197201 (2003). GC Milward, MJ Calderon, and PB Littlewood, Nature (London) 433, 607 (2005). J. Burgy, A. Moreo, and E. Dagotto, Phys. Rev. ... 93, 217402 (2004). S. Mercone, V. Hardy, C. Martin, Ch. Simon, D. Saurel and Annie Brûlet, Phys. Rev. B 68, 094422 (2003). ...
... Measurements for the triangular Ising-like cobaltite Ca 3 Co 2 O 6 have been made. Single cry... more ... Measurements for the triangular Ising-like cobaltite Ca 3 Co 2 O 6 have been made. Single crystals of Ca 3 Co 2 O 6 are found to exhibit a magnetodielectric effect below T N =25 K with a peak in the ε(H) curve at the ferri to ferromagnetic transition. ...
The slight incommensurate modulation of the structure of Bi(2)Mn(4/3)Ni(2/3)O(6) is sufficient to... more The slight incommensurate modulation of the structure of Bi(2)Mn(4/3)Ni(2/3)O(6) is sufficient to suppress the electrical polarization which arises in commensurate treatments of the structure, due to antiferroelectric coupling of local polar units of over 900 A(3). The incommensurate structure is produced by the competition between ferroelectric Bi lone pair-driven A site displacement, chemical order of Mn and Ni on the B site, and both charge and orbital order at these transition metals. The interplay between the frustrated polar Bi displacements and the frustrated spin order at the B site, induced by positional disorder, produces magnetodielectric coupling between the incommensurately modulated lattice and the spin-glass-like ground state with an unusual relationship between the magnetocapacitance and the applied field.
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Papers by Charles Simon