Spin-gap behavior of Na3Cu2SbO6 with distorted honeycomb structure

The spin-gap behavior observed in the temperature dependences of the magnetic susceptibility X and the specific heat C of Na3Cu2SbO6 with a (distorted) honeycomb structure is analyzed in detail. The behavior is commonly observed in similar systems A(3)Cu(2)SbO(6) and Na2Cu2TeO6 (A = Na, Li), and can be understood by considering both the significant Jahn-Teller distortion in the compounds and the characteristics of the shape of the electron orbits, in which spins exist. The behavior is contrasted with the antiferromagnetic transition in systems of Na3T2SbO6 and Na2T2TeO6 (T = Co, Ni). We point out that the antiferromagnetic-ferromagnetic alternating chain model successfully describes the observed magnetic behavior of Na3Cu2SbO6.