M – type hexaferrites, with general formula MeFe₁₂O₁₉ or MeO.6Fe₂O₃ (Me = Ba, Sr or Pb) exhibit a hexagonal symmetry, C6/mmc with two formula units per unit cell. They have interesting application not only as microwave devices but also as traditional permanent magnets, potential magneto – optical devices, high – density magnetic recording media (nanoscale) and compacts (submicron powders) for high – frequency devices. Substitution with non – magnetic ions such as Ga, In, Al, Sc etc. results in compounds which are paramagnetic at room temperature. The substitution with non – magnetic ions may change drastically the magnetic order of these compounds which may result in a shift from uniaxial to planar anisotropy, which is further useful in mm – wave devices. The intrinsic magnetic properties (i.e., saturation magnetization, anisotropy field) of these hexaferrites are strongly dependent on M – type phase. Substitution of Fe³⁺ cations leads to a reduction of the strong uniaxial magnetic anisotropy. The substitution of Ga & In in Sr hexaferrite crystals of the type SrGa_xIn_yFe_12-(x+y)O₁₉ (where x = 0, 5, 7, 9; y = 0, 0.8, 1.3, 1.0) decreases the value of magnetization which is attributed to shifting of collinear magnetic order to a non collinear one. Reduction of magnetization is also explained as a result of the occupation of the crystallographic sites of Fe³⁺ ions by Ga³⁺ & In³⁺. Substitution of Ga & In in Sr hexaferrite decreases the value of anisotropy field as well as anisotropy constant and the value of Curie temperature (T_c). The values of magnetization, anisotropy field, anisotropy constant and Curie temperature for Ga₇In_1.3 and Ga₉In_1.0 substituted Sr – hexaferrite could not be calculated as these crystals become paramagnetic at room temperature which is further confirmed by Curie temperature measurements. Further these crystals were irradiated with 50 MeV Li³⁺ ion beam at 15 MV Pelletron Accelerator at Inter University Accelerator Centre, New Delhi at four different fluences ranging from 1x10¹², 1x10¹³, 5x10¹³ and 1x10¹⁴ ions/cm².  Its effect on the materials depends on the ion energy, fluence, temperatures and ion species. Li³⁺ ion irradiation decreases the value of saturation magnetization, irrespective of whether the crystals are Ga – In substituted or unsubstituted Sr – hexaferrite crystals. Also the value of anisotropy constant decreases with the increase in the fluence values. The value of anisotropy field increases on irradiation and also with the increase in the value of fluences. The detailed results will be discussed and presented.