Magnetooptical investigation of Al-substituted yttrium iron garnets

The Faraday rotation (FR) of aluminium-substituted yttrium iron garnets single crystals of composition Y3|Fe2-xAlx| (Fe3-yAly) O12with O < x + y < 1.7 has been investigated at 1.15 micron wavelength in the temperature range 10°K < T < TN. The magnetooptical properties are analyzed from the two-sublattice Faraday effect model described by φF= - (Ae+Am) |Ma| + (De+Dm) |Md| where Ae, De, Am, Dmare the electric and magnetic dipole contributions the Faraday effect induced by the Fe³⁺ions in the octa and tetrahedral site having the magnetic moments Maand Md. From a non-linear dependence of the FR on (x + y), not explained from the associated decrease of Ma,d,it is shown that the Al substitution induces a strong decrease of the MO coefficients mainly in the octahedral site. This decrease of Ae(x, y) is determined and discussed from the corresponding dependences of the molecular field coefficients Naaand Nadon x and y.