Abstract
The structural phase transition in the orthovanadates and has been studied with high energy synchrotron x-ray diffraction. undergoes a second order phase transition at and a first order transition at while in CeVO3 there are phase transitions occurring at of second order and at of first order. These phase transitions are confirmed by specific heat measurements. The phase transition at in or in is due to a G-type orbital ordering which lowers the structure symmetry from orthorhombic to monoclinic The structure change at in is ascribed to an orbital ordering enhanced magnetostrictive distortion, while that at in is most probably due to an ordered occupation of the vanadium orbitals associated with an antiferromagnetic ordering. We propose that the first order phase transition at in should be associated with a sudden change of both spin and orbital configurations, similar to the phase transition at in [Ren et al., Nature (London) 396, 441 (1998)], causing a reversal of the net magnetization. However, the ordered state above in is identical to that below in It is found that, with increasing lanthanide ionic radius, the Néel temperature increases while the orbital ordering onset temperature decreases in these orthovanadates.
- Received 20 August 2002
DOI:https://doi.org/10.1103/PhysRevB.67.014107
©2003 American Physical Society