Magnetoentropic signatures of the textured metamagnetic phase of an antiferromagnetic polar metal. Ca₃Ru₂O₇

We report the magnetocaloric effect of a bilayered perovskite ruthenate Ca₃Ru₂O₇ that has recently been recognized as an antiferromagnetic polar metal. The magnetic entropy change obtained from temperature dependence of the DC magnetization measurements shows peaks and valleys under the magnetic field near metamagnetic transitions, and enable us to map out a thermodynamic field-temperature phase-diagram. The area surrounded by the boundaries agrees well with a novel "metamagnetic texture" with spin modulation observed recently by small angle neutron scattering measurements. We demonstrate that a thermodynamically equilibrium state is realized between the antiferromagnetic and spin-polarized states throughout the metamagnetic transition in this polar metal. (author)