Magnetic excitations in the metallic single-layer ruthenates Ca2−xSrxRuO

P. Steffens

¹

,

O. Friedt

²

,

Y. Sidis

³

et al.

Abstract

By inelastic neutron scattering, we have analyzed the magnetic correlations in the paramagnetic metallic region of the series Ca 2−x Sr x RuO 4 , 0.2 x 0.62. We find different contributions that correspond to twodimensional ferromagnetic fluctuations and to fluctuations at incommensurate wave vectors Q IC 1 = (0.11,0,0), Q IC 2 = (0.26,0,0), and Q IC αβ = (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 Ca 2−x Sr x RuO 4 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 Ca 1.38 Sr 0.62 RuO 4 with a low characteristic energy of 0.2 meV at T = 1.5 K, they are strongly suppressed in Ca 1.8 Sr 0.2 RuO 4 , 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.

Competition between spin fluctuations in Ca2−xSrxRuO4Arakawa1, Ogata2 2013Phys. Rev. B6040View full textAdd to dashboardCite

“…IV B, the enhancement of the main peak at q = (0,0) is consistent with several experiments. [18][19][20] We also find that the values of λ C max (q) −1 (not shown here) suppress as U increases. These results are qualitatively the same as those obtained in the previous study, 11 where the NNN hopping integral between the d xz and d yz orbitals has been neglected.…”

“…These results indicate that the FM spin fluctuation is predominant at a lower energy transfer, while the IC spin fluctuations evolve as an energy transfer increases. Furthermore, these measurements 19,20 have observed the intensity spreading in momentum space around the maximum peak and the large amplitude of the real part of the dynamic susceptibility at the maximum peak. These results indicate that several modes of spin fluctuation are more strongly enhanced for x = 0.62 than for x = 2, and that Ca 2−x Sr x RuO 4 with x = 0.62 is located nearer to the boundary of the magnetic instability.…”

“…In addition to this neutron measurement, the inelastic neutron measurements 19,20 for x = 0.62 have found that the FM scattering is maximum at an energy transfer of 0.4 meV, while the IC scatterings with q = (0.12,0,0) and (0.27,0,0) evolve at an energy transfer of ∼ 2.5 meV. These results indicate that the FM spin fluctuation is predominant at a lower energy transfer, while the IC spin fluctuations evolve as an energy transfer increases.…”

“…These bare vertex interactions are independent of the sublattice indices since the interacting Hamiltonian (20) is diagonal in terms of these indices. Since a phase transition is characterized by a divergence of static susceptibility, we calculate the eigenvalues of the static susceptibility by solving (35) c,d l…”

Persistence of antiferromagnetic order upon La substitution in the 4d4 Mott insulator Ca2RuO4

“…In particular, the emergence of an FM phase upon doping was predicted based on previous estimates of λ [11,20]. Experimental studies of doped Ca 2 RuO 4 , however, have mainly focused on the bandwidth control achieved by substitution of divalent Sr for isovalent Ca [21][22][23][24][25][26]. The investigation of the magnetic properties of the La-doped compounds have been limited to bulk magnetization measurements [27][28][29].…”