中国科学院半导体研究所机构知识库

随着人类社会的不断进步和信息技术的飞速发展，人们对高密度、非易失性、低功耗和高速智能的信息存储和处理的需求急剧增加。垂直磁各向异性材料在高灵敏度磁敏传感器、非易失性磁存储器和大功率微波振荡器等领域有着广泛的应用前景。作为典型的垂直磁各向异性材料，L1₀-MnGa受到了人们的高度关注。本论文利用分子束外延技术在GaAs衬底外延生长出高质量的L1₀-MnGa基磁性多层膜，并对结构、磁性进行了系统研究。其次，本文还研究了相关自旋电子学器件的输运行为。主要内容如下：

(1) 研究了高质量L1₀-MnGa/Co/MgO/Fe磁性隧道结中的隧穿磁电阻效应。L1₀-MnGa薄膜具有超高垂直磁各向异性、大矫顽力和高自旋极化度，是制备宽线性响应范围磁敏传感器的理想磁性参考层材料。超薄的Co (~0.8 nm)插层用于改善L1₀-MnGa和MgO的晶格失配并抑制Mn的扩散。对于垂直磁场探测，该磁性隧道结的室温隧穿磁电阻比值为27.4%，线性动态响应范围高达5600 Oe。同时，隧穿磁电阻曲线在动态响应范围内具有低非线性度和高可重复性。这些结果表明L1₀-MnGa基垂直磁性隧道结可以作为一种理想的高性能磁敏传感器。

(2) 研究了原位生长的L1₀-MnGa/FeMn双层膜中的自发垂直交换偏置现象。磁性和反常霍尔效应测量表明自发垂直交换偏置是该交换偏置系统中的本征特性。在低温下，磁滞回线的左右支存在明显的不对称性，这是由于磁化翻转过程中L1₀-MnGa/FeMn双层膜系统存在不同反相畴钉扎的磁畴壁翻转过程。垂直交换偏置场H_eb对温度T和反铁磁层厚度t_FeMn的依赖特性可以由反铁磁磁畴态模型解释。当温度为5 K时，在L1₀-MnGa (5 nm)/FeMn (8 nm)双层膜中观察到高达8.9 kOe的自发垂直交换偏置场H_eb。这一结果为在新型自旋电子学器件中无需外磁场辅助建立垂直交换偏置提供了实验参考。

(3) 研究了L1₀-MnGa/FeMn/AlO_x/Pt反铁磁性隧道结中的垂直隧穿各向异性磁电阻效应。由于交换弹簧作用，L1₀-MnGa中铁磁自旋可以驱动FeMn中反铁磁自旋发生部分转动，使隧穿态密度发生变化并导致隧穿各向异性磁电阻效应。隧穿各向异性磁电阻曲线在正、负场下分别呈高阻态和低阻态，表现出明显的磁滞特性。当温度为300 K时，隧穿各向异性磁电阻比值达到了0.86 %。隧穿各向异性磁电阻的角度依赖关系与其磁滞特性保持一致。随着温度升高，FeMn界面反铁磁自旋的向下分量变小，导致高电阻态和低电阻态的不对称性降低。这些实验结果为将来垂直反铁磁性隧道结的实际应用奠定了初步基础。

With the continuous development of modern human society and information technology, information storage and processing with ultrahigh-density, nonvolatility, low-energy consumption and high-speed are ugently needed. Materials with high perpendicular magnetic anisotropy (PMA) show many advantages in high-sensitivity magnetic sensors, nonvolatile magnetic memories and high-power oscillators. As a typical PMA material, L1₀-MnGa has attracted much attention. In this thesis, the structure, magnetic properties of L1₀-MnGa based magnetic multilayers have been investigated in detail. The electrical transport behviours of relavent spintronic devices have also been studied systematically. The main contents of this thesis are summarized as follows:

(1) We have investigated the tunneling magnetoresistance (TMR) effect in high-quality L1₀-MnGa/Co/MgO/Fe magnetic tunnel junctions (MTJs). Perpendicularly magnetized L1₀-MnGa is an ideal ferromagnetic material for reference layer in magtic field sensor for its large coercive force and high spin polarization. The insertion of thin Co layer between the L1₀-MnGa bottom electrode and MgO barrier layer is an effective approach to improve the interface quality and enhance the MR ratio. For perpendicular magnetic field sensing, the optimized MTJ shows large TMR ratio of 27.4% and huge linear dynamic range up to 5600 Oe at 300 K. Moreover, an ultra-low nonlinearity and excellent reproducibility have been confirmed in the dynamic range. All these results indicate that L1₀-MnGa based orthogonal MTJ structure is a promising candidate for high performance magnetic field sensor.

(2) We have demonstrated that the spontaneous perpendicular exchange bias (PEB) effect in as-grown L1₀-MnGa/FeMn bilayers. The static magnetic properties and anomalous Hall effect have demonstrated that the spontaneous PEB is an intrinsic property in this structure. The asymmetry of the hysteresis loop at low temperature is attributed to the different anti-phase domain nucleation center and unequal domain wall motion process. The temperature and FeMn layer thickness dependences of H_eb are explained by the antiferromagnetic domain state model. In particular, a large spontaneous PEB up to 8.9 kOe has been achieved in L1₀-MnGa (5 nm)/FeMn (8 nm) bilayers at 5 K. These results provide experimental basis for establishing PEB in spintronic devices without magnetic treatment.

(3) We have investigated the tunneling anisotropic magnetoresistance (TAMR) in antiferromagnet based tunnel junction with the structure of L1₀-MnGa/FeMn/AlO_x/Pt. Due to the exchange-spring effect, the partial rotation of antiferromagnetic spins in FeMn can be driven by perpendicularly magnetized L1₀-MnGa and leads to TAMR signals. The TAMR curves show hysteretic behavior with high-resistance state at positive field and low-resistance state at negative field. Specifically, the TAMR ratio reaches up to 0.86% at 300 K. The angular dependence of TAMR signal is well consistent with the hysteretic nature of the TAMR curves. Besides, the asymmetry between high-resistance state and low-resistance state declines at higher temperature due to the reduced downward component of interfacial FeMn spins. All these results lay the foundation of the future application of antiferromagnet based tunnel junction with out-of-plane TAMR at room temperature.