The spin Seebeck voltage was successfully increased by IrMn or Mn insertion into the interface Y3Fe5O12 and nonmagnetic Pt and TaW with positive and negative spin Hall angle, respectively. The magnitude of the spin Seebeck coefficient ∣S∣ of the samples with IrMn and Mn were higher than that with Ru insertion, which indicates that the existence of the magnetic moment is important for the spin Seebeck coefficient. Furthermore, ∣S∣ of the samples with IrMn and Mn were higher than oxide antiferromagnetic NiO, which suggests the metallic layer insertion is effective for enlarging ∣S∣ owing to the relatively long spin diffusion length. Since the inserted IrMn and NiO take the paramagnetic states as well as Mn, it is supposed that the spin fluctuation in the paramagnetic insertion layers play an important role in enhancing the spin current.

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We investigated the composition effect on spin Seebeck coefficient in YIG/Pt100−XRuX, YIG/Pt100−XCuX, and YIG/Pt100−X(Cu0.5Ru0.5)X systems. In all systems the composition of around 50 (at%) showed the maximum spin Seebeck coefficient, which is considered as the result from the extrinsic spin Hall effect improvement since the resistivity was also increased with doping Ru and Cu into Pt host. In terms of the spin Seebeck coefficient dependence on doped element, YIG/Pt100−XCuX was the largest, followed in order by YIG/Pt100−X(Cu0.5Ru0.5)X, and YIG/Pt100−XRuX, although both of Cu and Ru have equally small spin Hall angle in the single state. The X-ray diffraction analysis showed that Cu doping most widely decreased the unit cell size of alloy, and consequently increased the resistivity. It is considered as a reason of improvement of the extrinsic spin Hall angle and the spin Seebeck voltage.