氧化物隔离对Si基片上生长L1_0相FePt薄膜磁性的影响  

Effects of oxide isolation layer on magnetic properties of L1_0 FePt film grown on Si substrate

作　　者：李丹 李国庆[1] Li Dan;Li Guo-Qing(School of Physical Science and Technology,Southwest University,Chongqing 400715,China)

机构地区：[1]西南大学物理科学与技术学院,重庆400715

出　　处：《物理学报》2018年第15期337-344,共8页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:51071132)资助的课题~~

摘　　要：用MgO和SiO_2两种氧化物将FePt薄膜与Si(100)基片隔离,分析隔离层在FePt层发生A1→L1_0转变过程中的作用,寻找用Si母材涂敷L1_0-FePt磁性层来提高磁力显微镜针尖矫顽力的合理方案.采用磁控溅射法在400?C沉积Fe Pt薄膜,在不同温度进行2 h的真空热处理,分析晶体结构和磁性的变化.结果表明:没有隔离层,Si基片表层容易发生扩散,50 nm厚FePt薄膜的矫顽力最大只有5kOe(1 Oe=10~3/(4π)A·m^(-1));而插入隔离层,矫顽力可以超过10 kOe;MgO在Si基片上容易碎裂,热处理温度不能高于600?C,用作隔离层,FePt的最大矫顽力为12.4 kOe;SiO_2与Si基片的晶格匹配更好,热膨胀系数差较小,能承受的最高热处理温度可以超过800?C,使得Fe Pt的矫顽力可以在5 kOe到15 kOe范围内调控,更适合用于制作矫顽力高并可控的磁力显微镜针尖.Magnetic force microscope（MFM） is a powerful tool to subtly detect the stray field distribution of magnetic film or particles on a sub-micrometer scale. Due to its huge uniaxial magnetocrystalline anisotropy（Ku - 7 × 10^7 erg· cm^-3）and high Currie temperature（TC-500℃）, FePt alloy in an L10 phase is expected to be coated on the MFM tip to display high coercive force（Hc） and to improve the magnetic stability and MFM resolution. A grain size of - 3 nm will be enough to overcome the super paramagnetism. However, the growing fresh FePt films must experience a high temperature annealing（exceeding 700℃） in order to transform their structures thoroughly from a soft A1 phase into the desired hard L10 phase. This brings the risk of diffusion between FePt coating layer and the underneath Si cantilever.Several admixtures have been attempted by other researchers to obtain granular films with FePt grains separated by oxides, with the purpose to prevent the diffusion from happening between FePt and Si. But apparently, it will be very difficult to fabricate a separated FePt grain exactly on the top of MFM tip. This is a critical factor to affect the MFM resolution. And discussion about the influence of the interface diffusion is avoided in most of published papers.Alternatively, some oxide isolation layers with higher melting temperature can be useful for separating the top FePt film from the bottom Si crystal. In this paper, MgO and SiO2 are selected as isolation layers, deposited by magnetron sputtering. Subsequently, the FePt films are deposited at 400℃ and annealed at different temperatures（500℃ to800℃） for 2 h. The experimental results indicate that the diffusion between FePt and Si substrate always occurs in the absence of any isolation layer, leading to a reluctant maximum Hc of -5 kOe for 50 nm FePt film. However, the coercive force could remarkably exceed 10 kOe if an isolation layer is used. In the case of MgO, a maximum Hc of - 12.4 kOe for 50 nm FePt could be stably measured. Howe

关 键 词：FePt薄膜 Si基片 氧化物隔离层 热处理 

分 类 号：TN16[电子电信—物理电子学]