Recent progress of the bit patterned media fabricated by ion irradiation method is reviewed. High energy ion irradiation is a useful method to modify the magnetic properties and this technique can be used to fabricate high density bit patterned media which is a promising candidate to overcome the limit of the areal density of the conventional recording media. In order to achieve magnetic patterned structure having the feature size less than 50 nm by the ion irradiation technique, the materials whose magnetic order is easily suppressed by low dose ion irradiation are necessary. One of the candidate is L1₂ phase CrPt₃, and the control of the magnetic order of CrPt₃ by the ion irradiation and the fabrication of CrPt₃ bit patterned medium are discussed.