Dielectric Anomaly of ZnCr₂O₄at Antiferromagnetic Transition

Optical phonons, spin correlations, and spin-phonon coupling in the frustrated pyrochlore magnetsCdCr2O4andZnCr2Kant1, Deisenhofer2, Rudolf3 et al. 2009Phys. Rev. B713270View full textAdd to dashboardCite

“…14,15 The corresponding distortion in ZnCr 2 O 4 has been mostly described in terms of the tetragonal I4m2 space group also lacking inversion symmetry 3,13,16 but orthorhombic distortions have also been evoked leading to F222 symmetry 17 ͑no IS͒ or Fddd symmetry ͑conserving IS͒. 18 The number of infrared ͑IR͒ and Raman-active optical phonons strongly depends on the exact symmetry and occupied Wyckoff positions of the lattice. If inversion symmetry is present IR and Raman modes are mutually exclusive.…”

Magnetic Oxides

“…130, 131 The magnetic phase transition is remarkable in that it is first order rather than continuous as is usually found and there is a simultaneous crystallographic phase transition and a large dielectric anomaly. There is evidence for short range AF clustering at temperatures >100 K. These facts have led to speculation that the crystallographic phase transition is driven by a need to relieve the geometric frustration and arguments in terms of strain energies and magnetic energies.…”

Magnetic clusters in three dimensional spin frustrated system ZnCr2O4

“…We have proposed that the dielectric dispersion is due to the presence of two regions of different nature in a crystal. They are antiferromagnetic clusters accompanied with local lattice distortion and paramagnetic matrix surrounding them [2].The purpose of this study is to obtain further information about the magnetic clusters. From the view, we investigated AC magnetic susceptibility of pure ZnCr 2 O 4 and M .…”

“…We have proposed that the dielectric dispersion is due to the presence of two regions of different nature in a crystal. They are antiferromagnetic clusters accompanied with local lattice distortion and paramagnetic matrix surrounding them [2].…”

“…Our subject is to know how a strong frustration can be relaxed below T N : Previously, we discussed a possible process of the antiferromagnetic transition as follows [2]. (1) ZnCr 2 O 4 is in an ordinary paramagnetic state above 100 K. (2) Antiferromagnetic clusters begin to develop around 100 K. Two magnetically different regions coexist in a crystal at temperatures higher than T N : (3) The antiferromagnetic short-range order does not develop into the long-range order. Another phase with a different type of antiferromagnetic order, characterized by ðh=2 k lÞ and ðh=2 k=2 lÞ magnetic Bragg reflections, appears abruptly at T N [3].…”