Magneto-capacitive coupling and hybridization driven structural anomalies in Spinels
Zusammenfassung der Projektergebnisse
Within our project we have grown, characterized and investigated high-quality single crystals of a larger number of spinel systems with highly correlated magnetic and structural properties. The involved techniques were X-ray diffraction including synchrotron radiation, SQUID magnetometry, optical and Raman spectroscopy, as well as ultrasound spectroscopy in high magnetic fields. In spinels (AB2X4) the occupation of the A and B sites with magnetic (Fe; Cr,...) or nonmagnetic (Cd, Hg, Zn...) ions determines possible exchange paths and orbital degrees of freedom. The magnitude and sign of the exchange as well as a possible competition of interactions are determined by the X anions, here S, Se and O. In our project we have found a systematic dependence of the interaction and competition of spin and lattice degrees of freedom on the composition of the studied material. Interesting cases concern spin frustration due to competing interactions that lead to exotic instabilities and a large sensitivity or amplification of external fields (strain, electric and magnetic fields). As a result, e.g. giant magnetocapacitive effects have been observed and studied in CdCr2S4 and manipulated by doping using sulfur nonstoichiometry. Novel magnetostructural states were found in high magnetic fields in ZnCr2S4 with strongly frustrated exchange interactions. The effect of orbital degeneracy has been studied in FeCr2S4 that shows colossal magnetocapacitance. We reported for the first time the structural transformation that accompanies the orbital order transition, thus solving a long-standing problem in this compound. Different spin-phonon coupling mechanisms have been evaluated by comparing geometrically frustrated CdCr2O4 and ZnCr2O4 spinels leading to a microscopic understanding that did not exist before. The resulting data base is now in use by several research groups, e.g. to refine theoretical models using DFT calculations. Comparably large single crystals that have been grown during the project allowed and will allow future studies that could not have been performed before, e.g. ultrasound and neutron scattering. Unfortunately, some compounds did not show a considerable improvement of sample quality. We have shifted these systems to our roadmap for future investigations, examples are HgCr2S4 and HgCr2Se4.
Projektbezogene Publikationen (Auswahl)
- “Optical phonons, spin correlations, and spin-phonon coupling in the frustrated pyrochlore magnets CdCr2O4 and ZnCr2O4”, Phys. Rev. B 80, 214417 (2009)
Ch. Kant, J. Deisenhofer, T. Rudolf, F. Mayr, F. Schrettle, A. Loidl, V. Gnezdilov, D. Wulferding, P. Lemmens, V. Tsurkan
- “Lattice Instabilities in the Frustrated Magnet CdCr2O4: An Ultrasonic Study”, J. Low. Temp. Phys. 159, 134-137 (2010)
S. Zherlitsyn, O.·Chiatti, A. Sytcheva, J. Wosnitza, S. Bhattacharjee, R. Moessner, M. Zhitomirsky, P. Lemmens, V. Tsurkan, A. Loidl
- “Structural anomalies and the orbital ground state in FeCr2S4”, Phys. Rev. B 81, 184426 (2010)
V. Tsurkan, O. Zaharko, F. Schrettle, Ch. Kant, J. Deisenhofer, H.-A. Krug von Nidda, V. Felea, P. Lemmens, J.R. Groza, D.V. Quach, F. Gozzo, A. Loidl
- “Interplay of spin and lattice degrees of freedom in the frustrated antiferromagnet CdCr2O4: High-field and temperature-induced anomalies of the elastic constants”, Phys. Rev. B 83, 184421 (2011)
S. Bhattacharjee, S. Zherlitsyn, O. Chiatti, A. Sytcheva, J. Wosnitza, R. Moessner, M. E. Zhitomirsky, P. Lemmens, V. Tsurkan, and A. Loidl
- “Magnetostructural Transitions in a Frustrated Magnet at High Fields”, Phys. Rev. Lett. 106, 247202 (2011)
V. Tsurkan, S. Zherlitsyn, V. Felea, S. Yasin, Yu. Skourski, J. Deisenhofer, H.-A. Krug von Nidda, P. Lemmens, J. Wosnitza, and A. Loidl
- “Phonon anomalies and possible local lattice distortions in giant magnetocapacitive CdCr2S4”, Phys. Rev. B 84, 045106 (2011)
V. Gnezdilov, P. Lemmens, Yu. G. Pashkevich, Ch. Payen, K. Y. Choi, J. Hemberger, A. Loidl, and V. Tsurkan
- Spin–lattice coupling and structural transformations in frustrated magnets with spinel structure and MnWO4. PhD Thesis, Institute of Applied Physics of the Academy of Sciences of Moldova on February 10, 2012
Viorel Felea
