Laser and thermal annealings of Bi,Ga- and La,Ga-substituted garnet films

Abstract

Strong change of the saturation magnetization 4πMs and the bubble parameters such as wall energy, bubble diameter, and material characteristic length have been observed from bubble statics experiments after heat treatment corresponding to annealing and quenching processes either from usual furnace or from laser annealing. The changes of physical properties are associated with cation migration between the octa- and tetrahedral sites in both the La,Ga-YIG and Bi,Ga-YIG films we have investigated. After annealing in oxygen ambient in a furnace at different equilibrium temperatures between 1125 and 1473 K, the films with the total Ga content between 1 and 1.23 were quenched. In a second step laser annealed channels were produced on the same films and their profile analyzed from the comparison with data obtained after normal furnace annealing. Strong differences were observed after furnace and laser annealings between Bi,Ga- and La,Ga-substituted YIG. Irreversible processes arise after furnace annealing in bismuth garnet mainly for uniaxial anisotropy, in-plane saturation field and quality factor Q, which is not the case in La,Ga-YIG films. In addition, due to different kinetic processes for Bi3+ and Ga3+ ions associated with heat treatment, laser annealing induces large modifications for magnetic properties associated only with Ga3+ migration, whereas uniaxial anisotropy resulting from Bi3+ ion ordering is perturbed only a little. The data is discussed from the Néel molecular field theory and the Van Erk thermodynamic equilibrium model.