It is shown that interlayer spin-singlet Cooper pairing is induced by magnetic interactions in a metallic antiferromagnet of stacked conductive layers in which each layer is ferromagnetically polarized and they order antiferromagnetically in stacking direction. As a result, the antiferromagnetic long-range order and superconductivity coexist at low temperatures. It is shown that TAF > Tc except for in a very limited parameter region unless TAF = 0, where TAF and Tc denote the antiferromagnetic and superconducting transition temperatures, respectively. It is found that the exchange field caused by the spontaneous staggered magnetization does not affect superconductivity at all, even if it is very large. The resultant superconducting order parameter has a horizontal line node, and is isotropic in spin space in spite of the anisotropy of the background magnetic order. We discuss the possible relevance of the present mechanism to the antiferromagnetic heavy fermion superconductors UPd2Al3 and CePt3Si. PACS numbers: 74.20.Mn, 74.20.Rp 74.25.Ha In this paper, we show that interlayer spin-singlet Cooper pairing is induced by magnetic interactions in a certain kind of metallic antiferromagnet. We consider a layered system of itinerant electrons in which each layer is ferromagnetically polarized but the majority-spin alternates in stacking direction. Therefore, the magetic order is characterized by the wave vector Q = (0, 0, π/c), where we have assumed the a and b crystal axes to be parallel to the layers, and the c-axis in the stacking direction, and c denotes the c-axis lattice constant. It is also shown that the exchange field caused by spontaneous staggered magnetization does not influence superconductivity, however large it is. The heavy fermion superconductors, such as UPd 2 Al 3 and CePt 3 Si, can be candidates of the present mechanism. The antiferromagnetic long-range order is considered to be characterized by the wave vector Q = (0, 0, π/c), both in UPd 2 The order parameter of interlayer spin-singlet pairing has a horizontal line node. This also agrees with the experimental results in the compound UPd 2 Al 3 . The existence of the line node is suggested by the nuclear magnetic resonance (NMR) measurement Coexistence of superconductivity and magnetism has been studied in various models by many authors The magnetic structure mentioned above can be modeled most simply by the Hamiltonian with the kinetic energy term the on-site Coulomb interactions and the exchange interactions We have defined S i = 1 2 σσ ′ c † iσ σ σσ ′ c iσ ′ , n i = σ n iσ , and n iσ = c † iσ c iσ , where σ denotes the vector of Pauli matrices, and c kσ and c iσ denote the electron operators. We define J ij = J > 0 for R j = R i ±ĉ, J ij = −J < 0 for nearest neighbor sites (i, j) on the same layer, an
