A method of surface oxidization of a CoCrZr seed layer has been developed. This method can control the microstructure of a CoCrPt/CrTi thin film medium on the glass substrate. By exposing the surface of the CoCrZr seed layer to just a little oxygen (in the order of 10-5 Torr), the crystal orientation of the CrTi underlayer deposited on the seed layer is changed from (110) to (200). The crystal grain size of the underlayer is also affected, and smaller grains can be obtained by the surface oxidization of the seed layer. These changes in microstructure of the CrTi underlayer result in magnetic crystal grains with small grain size and in-plane c-axis orientation. Both these properties improve the read/write performance considerably.