Itinerant metamagnetism of CeRu₂Si₂: Bringing out the dead. Comparison with the new Sr₃Ru₂O₇ case

Focus is given on the macroscopic and microscopic experimental works realized during a decade on the clear case of itinerant metamagnetism in the heavy fermion paramagnetic compound CeRu₂Si₂. Emphasis is made on the feedback between the band structure, the exchange coupling and the lattice instability. Sweeps in magnetic field, pressure and temperature feel the pseudogap of this strongly correlated electronic system as well as its equivalent CeRu₂Ge₂ at a fictitious negative pressure. Some mysteries persist as the complete observation of the Fermi surface above the metamagnetic field H_M and the detection of the dynamical ferromagnetic fluctuation near H_M. The novelty of the bilayer ruthenate Sr₃Ru₂O₇ is discussed by comparison. Despite differences in spin and electronic dimensionality many common trends emerge.