Magnon energy gap and quantum fluctuation in a ferro-anti-ferromagnetic multisublattice system

Within the framework of the linear spin wave approximation and the retarded Green's function method, the magnetic properties of a ferro-anti-ferromagnetic Heisenberg system are studied. Under certain cases, five magnon energy gaps exist in the energy band. The effects of upper surface anisotropy, spin numbers, exchange coupling, and antiferromagnetic intralayer exchange coupling on magnon energy gaps, as well as the effects of the interlayer exchange couplings on magnetization and quantum fluctuation, are discussed. Results show that antiferromagnetic (ferrimagnetic) interlayer exchange coupling plays a significant role in the magnetic properties of the system.