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Recently, the first study of the e ects induced by the substitution of the magnetic impurity (Ir4+) and the nonmagnetic impurity (Ti4+) in the RuO2 planes has been performed [41]. Here, the observed e ects are also quite peculiar. Similarly to cuprates, the substitution of the nonmagnetic impurity Ti4+ (3d0) in Sr2RuO4 induces a local magnetic moment with an e ective moment0.5µB /Ti [42]. The induced moment has Ising anisotropy with an easy axis along the c direction. Furthermore, magnetic ordering with glassy behavior appears for x(Ti) > 0.025 in Sr2Ru1−xTixO4, while the metallic conduction in the in–plane direction is retained. When x is increased further to 0.09, elastic neutron scattering measurements detect an incommensurate Bragg peak whose wave vector Qic (2π/3, 2π/3) is close to the position of the inelastic neutron scattering peak in pure Sr2RuO4 [43]. Most interestingly, in the vicinity of a magnetic ordering, a deviation from the pure Fermi liquid behavior seen in Sr2RuO4 is observed by means of resistivity and transport measurements, which show linear and logarithmic temperature dependence, respectively [44]. These results indicate that the two–dimensional incommensurate antiferromagnetic spin fluctuations arising from the nesting of xz and yz bands become a static spin density wave state when Ti is substituted. On the other hand, the system Sr2Ru1−xIrxO4 in which the substitutional impurity is the magnetic Ir4+ (5d5 in the low spin configuration), shows a weak ferromagnetism for x(Ir) > 0.3 [45]. Thus, substitution of magnetic and nonmagnetic impurities in Sr2RuO4 leads to di erent ground states. In short, despite these di erences, both magnetic and nonmagnetic impurities act similarly because both reduce Tc. Thus, one might conclude that magnetic and nonmagnetic impurities act mainly as potential scatterers and that magnetic scattering does not play a particular role. To some extent, this observation is consistent with the existence of a spin triplet state because magnetic impurities break up singlet Cooper pairs, mainly as a result of exchange splitting, while an equally paired spin state would not be a ected.

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