Effect of Partial Oxygen Pressure on Magnetic Properties of Strontium Ferrite Thin Films

Abstract

Abstract~Strolltiurn hexagonal ferrite (SrM) thin films were prepared with a dc magnetron sputtering system,and the crystal structure and magnetic properties were studied. It was found that structural and magnetic properties of the films prepared at the substrate temperature (Ts) of 600"0 were affected by partial oxygen pressure (P02 ) as compared with those of the fihn prepared at Ts of 550"0. The coercivity of each film prepared at Ts of 550"0 was about 5kOe in the pel'pendicular direction, although that of the films prepared at the Ts of 600°0 and P02 of 10% was about 2kOe with preferentiai orientation of c-axis was observed. The grain size of the films prepared at the Ts of 600"0 was larger than that of other films. It co'tlld be considered that growth of the grains lead to the decrease of the coerdvity. IN'l'aODUCTloNStront,ium hexagonal ferrite (SrM) thin films with the magnetoplumbite type (M~type) crystal structure as well as barium ferrite (DaM) thin films are expected to be high density recording media because of their chemical stability, mecbanical hardness, and moderate hard magnetic properties [11-(21. It is possible to use hexagonal ferrite films a.<; longitudinal and perpendicular recording media in the next generation by shifting tbe c-axis orientation. It is reported tbat SrM has higher coercivity than that of DaM [3]-[5], Therefore we have attempted to modify the SrM film to the properties suitable for the recording medium 1 • The SrM thin films were prepared at various partial oxygen pressure (P02 ), and their crystal structure and magnetic properties were studied. rI, EXPERIMENTALThe SrM films Were prepared with a dc magnetron sputtering system. A sintered ferrite disk with the stoichiometric composition of M~type, i.e. Sr:Fe = 1:12, was used as the target. The substrate temperature (Ts) was 550 and 600 <>C. Thermally oxidized silicon wafers were used as the substrate and the thickness of the films were about 1500 A. The films were prepared at the total gas pressure of 2 mTorrand the partial oxygen pressure (POll ) was varied from 0 to 40 %.Ill. RESULTS AND DISCUSSfON Fig.1 shows X-ray diffraction (XRD) diagrams for the films prepared at Ts of 600°C. The lines of SrM phase were observed on eaeh diagran~ when the P02 was 10%. The most of lines were predominantly from e-plaue of hexagonal structure when the P0 2 was 10%. 'However when the Poz was higher than 10%, the orientation of the films were random. So tl1a,t it was considered that 4:00. high P02 disturbed the orientation of the films at Ts of 600°C. Tbe films prepared at Ts of 550 <>C became random orientation. It was because that the Ts was not enough to orient the films to thee-plane. . Fig.2 shows the surface structure of the films prepared at various Po z observed with SEM. The grains of the film prepared at Ts of 550°C looks like needle or chunk. The grain size were about 500 A audit was -194-