Deaprtment of Physics, University of Jammu^* Inter University Accelerator Centre, Aruna Asif Ali Marg, New Delhi-110067 (India)^** Institue of Maspec, Italy^***
○Krishen Kumar Bamzai^* Balwinder Kaur^* Pushkar Nath Kotru^* Ravi Kumar^** F Licci^***

Hexagonal ferrites, which is represented by MeFe₁₂O₁₉ (where Me=Ba, Sr or Pb) belongs to a class of ferromagnetic oxides. Attempt to improve the magnetic properties of these ferrites was done by substituting Fe³⁺ ions with some non magnetic ions (i.e., Ga, In, Sc & Al). These substitutions lead to drastic variation in the magnetic structures of hexaferrites. 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⁺. Changes in their magnetic structures can also be brought about by swift heavy ions. Swift heavy ions in the MeV range causes modifications in the materials which entirely changes their magnetic structure. 50 MeV Li³⁺ ion irradiation decreases the value of magnetization irrespective of whether the crystals are Ga & In substituted or unsubstituted. The results are interpreted in terms of occurrence of a paramagnetic doublet in crystals replacing magnetic sextuplet as a result of irradiation. Substitution of Ga & In in Sr hexaferrite decreases the value of anisotropy field as well as anisotropy constant. Irradiation with Li³⁺ ions increases the value of H_a for both substituted as well as unsubstituted crystals. Substitution with Ga & In also decreases the value of Curie temperature (T_c) but the irradiation with Li³⁺ ions does not affect the T_c of either substituted or pure SrFe₁₂O₁₉ crystals.