Theory for the magnetic phase diagram of thin films: Role of domain formation

The magnetic phase diagram of a thin film is determined at T=0. The exchange coupling, the magnetic dipole coupling, as well as the second- acid fourth-order lattice anisotropies are taken into account. The long-range dipole coupling causes an instability of the uniform magnetization with perpendicular orientation and leads to a domain phase. Four different phases, in particular stripe domain structures with perpendicular and canted orientations of the domain magnetization, are found to be stable. The parameter region near the magnetic reorientation is studied in greater detail. It is shown that the higher-order lattice anisotropies may induce a continuous reorientation from a perpendicular to an in-plane magnetization, also for a domain phase. By carrying out lattice sums we conclude that a periodic array of straight domain wails should be stable against spatial dislocations. Our results suggest that the domain phases may alter the nature of the phase transitions at finite temperatures in thin films. Rather than phase transitions with critical phenomena a simple rotation of the magnetization might occur.