Preferred Crystal Orientation and its Effect on the Magnetization Reversal Property of CoCrTa Thin Films
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Mat. Res. Soc. Symp. Proc. Vol. 403 01996 Materials Research Society
EXPERIMENT The approach of this investigation was to sputter deposit CoCrTa thin films on various nonmagnetic underlayers in order to discover the relationship between the crystal orientation distribution and the magnetization reversal properties of the sample films. Sample films were RF sputter deposited on two different non-magnetic underlayers using a Perkin-Elmer 2400 8SA RF diode sputtering system. The CoCrTa thin films were deposited at 3.08 Watt/cm 2 RF power density from an eight-inch diameter target with 10 mtorr of Argon sputtering gas pressure. Two different underlayers were used in this study; they were thermally grown silicon dioxide (Si0 2 ), and thin tantalum nitride (TaN). The tantalum nitride was sputter deposited at room temperature on a silicon wafer coated with thermally grown silicon dioxide. It has been reported that thin tantalum nitride appears to foster the formation of NiFe [111] preferred crystal orientation [9]. Also, the atomic arrangement of the NiFe (111) plane has been reported to be well matched to the CoCrTa (00.2) plane [8]. Thus, a strong perpendicular CoCrTa [00.2] preferred crystal orientation distribution is expected for CoCrTa films deposited on thin tantalum nitride underlayers. Subsequent to the deposition, the magnetic properties of the sample films were characterized by a vibrating sample magnetometer (VSM) and a torque magnetometer at a maximum applied magnetic field of 12 KOe. The crystallographic structure was examined using X-ray diffractometry. X-ray diffraction data were obtained with a Siemens D500 unit using Cu Ka radiation and a graphite single crystal monochromater mounted just before the counter. The c-axes dispersion, A0 50 , of the CoCrTa was determined by an X-ray rocking curve method using the hcp (00.2) diffraction peak. Diffraction patterns were obtained in the Bragg-Brentano 20/0-mode, while A0 50 rocking curves were obtained in the 0-mode (counter fixed at 2 times Bragg angle OB for a given peak). The surface morphology of the sample films was also examined by an atomic force microscope (AFM). RESULTS AND DISCUSSION Non-magnetic underlayers are used to foster nucleation and growth of CoCrTa hcp (00.2), allowing correlation between the crystal orientation distribution and the magnetization reversal properties of the CoCrTa thin films. A strong CoCrTa [00.2] perpendicular crystal orientation distribution is expected for CoCrTa films deposited on thin tantalum nitride underlayers, while a random crystal orientation distribution is expected for CoCrTa films deposited on Si0 2 underlayers. The X-ray diffraction results for CoCrTa films deposited on the two underlayer types are shown in Fig. 1. No substrate bias was applied during the deposition of CoCrTa and no significant difference in crystal orientation distribution was found in the two sample films. The A0 50 values for the CoCrTa (00-2) diffraction peak obtained from X-ray rocking curves of the sample films were 150 and 130, respecti
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