Magnetoelastic Coupling Across the Metamagnetic Transition in Ca2-xSrxRuO4$${(0.2\leq x\leq 0.5)}$$

The magnetoelastic coupling in Ca1.8Sr0.2RuO4 and in Ca1.5Sr0.5RuO4 has been studied combining high-resolution dilatometer and diffraction techniques. Both compounds exhibit strong anomalies in the thermal-expansion coefficient at zero and at high-magnetic field as well as an exceptionally large magnetostriction. All these structural effects, which are strongest in Ca1.8Sr0.2 RuO4, point to a redistribution of electrons between the different t2g orbitals tuned by temperature and magnetic field. The temperature and the field dependence of the thermal-expansion anomalies in Ca1.8Sr0.2RuO4 yield evidence for a critical end-point lying close to the low-temperature metamagnetic transition; however, the expected scaling relations are not well fulfilled.