Orbital-ordering-induced phase transition in LaVO3 and CeVO3

概要

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The structural phase transition in the orthovanadates LaVO3 and CeVO3 has been studied with high energy synchrotron x-ray diffraction. LaVO3 undergoes a second order phase transition at TN = 143 K and a first order transition at Tt = 141 K, while in CeVO3 there are phase transitions occurring at T0 = 154 K of second order and at TN = 134 K of first order. These phase transitions are confirmed by specific heat measurements. The phase transition at Tt in LaVO3 or T0 in CeVO3 is due to a G-type orbital ordering which lowers the structure symmetry from orthorhombic Pbnm to monoclinic P2t/b11. The structure change at TN in CeVO3 is ascribed to an orbital ordering enhanced magnetostrictive distortion, while that at TN in LaVO3 is most probably due to an ordered occupation of the vanadium 3d t2g orbitals associated with an antiferromagnetic ordering. We propose that the first order phase transition at Tt in LaVO3 should be associated with a sudden change of both spin and orbital configurations, similar to the phase transition at Ts = 77 K in YVO3 [Ren et al., Nature (London) 396, 441 (1998)], causing a reversal of the net magnetization. However, the ordered state above Tt in LaVO3 is identical to that below Ts in YVO3. It is found that, with increasing lanthanide ionic radius, the Néel temperature TN increases while the orbital ordering onset temperature decreases in these orthovanadates.
American Physical Societyの論文
2003-01-24