Magnetic excitations in the metallic single-layer ruthenates Ca2-xSrxRuO4 studied by inelastic neutron scattering

By inelastic neutron scattering, we have analyzed the magnetic correlations in the paramagnetic metallic region of the series Ca2-xSrxRuO4, 0.2 <= x <= 0.62. We find different contributions that correspond to two-dimensional ferromagnetic fluctuations and to fluctuations at incommensurate wave vectors Q(1)(IC) = (0.11,0,0), Q(2)(IC) = (0.26,0,0), and Q(alpha beta)(IC) = (0.3,0.3,0). These components constitute the measured response as a function of the Sr concentration x, of the magnetic field, and of the temperature. A generic model is applicable to metallic Ca2-xSrxRuO4 close to the Mott transition, in spite of their strongly varying physical properties. The amplitude, characteristic energy, and width of the incommensurate components vary only slightly as functions of x, but the ferromagnetic component depends sensitively on concentration, temperature, and magnetic field. While ferromagnetic fluctuations are very strong in Ca1.38Sr0.62RuO4 with a low characteristic energy of 0.2 meV at T = 1.5 K, they are strongly suppressed in Ca1.8Sr0.2RuO4, but reappear upon the application of a magnetic field, and form a magnon mode above the metamagnetic transition. The inelastic neutron scattering results document how the competition between ferromagnetic and incommensurate antiferromagnetic instabilities governs the physics of this system