Structural aspects of metamagnetism in Ca2-xSrxRuO4: evidence for field tuning of orbital occupation.

The crystal structure of Ca(2-x)Sr(x)RuO(4) with 0.2 < or = x < or = 1.0 has been studied by diffraction techniques and by high resolution capacitance dilatometry as a function of temperature and magnetic field. Upon cooling in zero magnetic field, the crystal structure and the octahedra shrink along the c direction and elongate in the a and b planes, whereas the opposite occurs upon cooling at high field (x = 0.2 and 0.5). These findings yield evidence for an orbital rearrangement driven by temperature and magnetic field, which accompanies the metamagnetic transition at low temperature. The temperature and magnetic-field dependencies are found to be governed by the same energy scale.