Double metamagnetic transition in Sr4 Ru3 O10

We report a magnetization study down to 1.7 K for the trilayered ruthenate Sr4Ru3O10 for magnetic fields applied within the ab plane. Our measurements reveal that the metamagnetic jump appearing in the isothermal magnetization curves below TM=68 K is actually composed of two consecutive metamagnetic transitions, where the increase in the magnetization due to the second transition is roughly one third of the overall metamagnetic jump. We show that the metamagnetic critical fields for these two transitions increase as the temperature decreases, and that their difference has a weak temperature dependence that opens up in the proximity of the critical region near TM. We discuss the origin of this double metamagnetic transition being due to either the ordering of the Ru 4d magnetic moments in the two inequivalent crystallographic Ru sites or to the presence of two van Hove singularities in the near-Fermi-level density of states.