Estimation of Magnetic Energy Distribution in Co 84 Cr 16 Ta 4 Magnetic Thin Films from EFTEM
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1026-C03-05
Estimation of Magnetic Energy Distribution in Co84Cr16Ta4 Magnetic Thin Films from EFTEM Jafar F. Al-Sharab1, James E Wittig2, James Bentley3, Neal Evans3, Gerardo Bertero4, and Tom Yamashita4 1 Materials Science and Engineering, Rutgers University, 607 Taylor RD, Piscataway, NJ, 08854 2 Electrical Engineering and Computer Science, Vanderbilt University, Nashville, TN, 37234 3 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, 37831 4 Komag Inc., San Jose, CA, 95131 Keywords: KuV distribution, EFTEM, CoCrTa thin films, Magnetic Energy distribution, Longitudinal magnetic thin films. Abstract Magnetic thin films of Co80Cr16Ta4 were sputtered onto identical CrMo seed-layers at –200 V bias and 3 different substrate temperatures (150, 200, and 250oC). Energy-filtered transmission electron microscopy (EFTEM) was performed to analyze Cr levels at the grain boundaries as well as inside the grains. These quantitative Cr measurements were used to estimate the local values of magnetocrystalline anisotropy (Ku) and, together with grain size distributions, calculate the product of Ku and the grain volume (KuV), a quantity which is a measure of thermal stability. The results show that the coercivity as well as the fraction of stable grains increased with increasing substrate temperature. The increase in the fraction of stable grains is produced by the enhancement in the Ku value due to Cr depletion of the grain interiors and the magnetic decoupling between the grains from Cr grain-boundary segregation. Introduction Thin films of CoCr(PtTa) with Cr underlayers are still the standard materials used for high areal density longitudinal recording media. Since the performance of these Co-Cr based media is strongly dependent on their nano-scale structure and chemistry, structure-property correlations require detailed microstructural characterization. A critical microstructural feature in sputtered thin films of CoCr(PtTa) is the Cr grain boundary segregation that produces magnetic isolation between grains [1]. The concomitant Cr depletion within the grain interiors also influences recording properties such as thermal stability, since saturation magnetization Ms and magnetocrystalline anisotropy Ku are sensitive to local Cr content [2]. The thermal stability of the magnetic media is related to the magnetic switching energy (KuV) and the thermal energy (kT) from KuV/kT > s, where V = the grain volume, k = Boltzmann’s constant and T = temperature [3]. The parameter, s, can be used to define conditions for thermal stability where s should be greater than 45 to 60 to ensure stability [4,5]. A conservative approach, based on a maximum loss of 5% of the stored information at ambient temperature over 10 years, requires that s must be greater than 60 [5]. The thermal energy, kT, reduces thermal stability as the harddisk-drive temperature increases to 70-80oC [6] during the recording process. Therefore it is essential to have high magnetic energy, KuV, to prevent the spontaneous switching of the
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