Analysis on high-field magnetic properties of aluminum substituted rare-earth iron garnet at low temperatures

Magnetic properties of aluminum substituted erbium and holmium iron garnets (Er3Fe4.65Al0.35O12, Er3Fe4.45Al0.55O12 and Ho3Fe4.55Al0.45O12) are theoretically investigated by a three-sublattice model in high magnetic fields up to 200 kOe applied along the three principal crystallographic directions [100], [110] and [111] at low temperatures (4.2 K and 30 K). The effect of the substitution of the diamagnetic Al3+ ion, located in tetrahedral site, on the exchange interaction in rare-earth iron garnets is analyzed. The temperature and field dependence of the magnetization in a, c and d sublattices, labeled as Ma, Mc and Md, are analyzed, where obvious anisotropies are revealed. Correspondingly, it is further pointed out that the anisotropy of magnetic properties mainly arises from the contribution of exchange interaction. Excellent fits to the experimental magnetization are carried out, from which the parameters αi (i=a, c, d) associated with the exchange interaction and the effective magnetic susceptibility are determined. At a certain temperature, the parameters conform to the expression αi=P1+P2He−1+P3He−2, where P1, P2 and P3 are the coefficients, He is the external magnetic field.