16:00 〜 18:00
▲ [17p-P10-81] Optimization of Fabrication Temperature to Obtain L10-Ordered MnAl Thin Films with High Perpendicular Magnetic Anisotropy and Small Roughness
キーワード：Magnetic tunnel junction, Saturation magnetization, STT-MRAM
Magnetic tunnel junction with perpendicularly magnetized ferromagnetic materials (p-MTJs) have great potential to realize the ultra-high-density STT–MRAM.The switching current density (Jco) in STT-MRAM is directly related to saturation magnetization (Ms) and Gilbert damping constant (α) of the ferromagnetic free layer of MTJs .In order to achieve high thermal stability and low switching current density in p-MTJs, ferromagnetic materials with large perpendicular magnetic anisotropy energy (Ku), small Ms and low α are required. Here, we focus on a L10-MnAl alloy, which exhibits small Ms and high Ku. In our previous works, we obtained large Ku in L10-MnAl films prepared at high substrate temperature. However, high substrate temperature can cause increasing roughness of the films and atomic diffusion between the MnAl films and their buffer layers. In this work, we systematically investigated substrate and annealing temperature dependences of structural and magnetic properties in the MnAl thin films to achieve both high Ku and small surface roughness.
The film stacking structure was MgO(001)-sub./CrRu(40)/Mn-Al(50)/Ta(5)(in nm). All the films were prepared by a magnetron sputtering system. The Mn-Al alloy target composition was Mn46Al54.The substrate temperature (Ts) during deposition was varied from 2000C to 4000C and the post-annealing temperature (Ta) was varied from 2000C to 5000C. The crystal structure of MnAl(50nm) films was investigated by an X-ray diffraction (XRD). The magnetic properties and surface morphology of the films were measured by vibrating sample magnetometer (VSM) , superconductive quantum interference device (SQUID) and atomic force microscopy (AFM).
We confirmed that CrRu buffer layers had good structural property and very smooth surface morphology after annealing at 6500C. In the XRD patterns, (001) and (002) peaks of L10-MnAl were observed.The result indicates that both L10-ordered and (001)-oriented MnAl films were successfully fabricated. The peak intensity of L10-MnAl was improved with increasing both substrate and annealing temperature. However, surface roughness drastically increased above Ts=3000C. We systematically investigated annealing temperature dependence of magnetic properties in MnAl films prepared with Ts = 2500C. As a result, Ku showed a maximum at Ta = 3500C as shown in Fig. 1, and finally obtained a L10-ordered MnAl film with high Ku of 13.0 Merg/cc, relatively low Msof 497 emu/cc and small roughness (Ra) of 0.3 nm in the condition of Ts= 2500C and Ta=3500C. The optimized MnAl film will be greatly useful to realize the high-density STT-MRAM.
The film stacking structure was MgO(001)-sub./CrRu(40)/Mn-Al(50)/Ta(5)(in nm). All the films were prepared by a magnetron sputtering system. The Mn-Al alloy target composition was Mn46Al54.The substrate temperature (Ts) during deposition was varied from 2000C to 4000C and the post-annealing temperature (Ta) was varied from 2000C to 5000C. The crystal structure of MnAl(50nm) films was investigated by an X-ray diffraction (XRD). The magnetic properties and surface morphology of the films were measured by vibrating sample magnetometer (VSM) , superconductive quantum interference device (SQUID) and atomic force microscopy (AFM).
We confirmed that CrRu buffer layers had good structural property and very smooth surface morphology after annealing at 6500C. In the XRD patterns, (001) and (002) peaks of L10-MnAl were observed.The result indicates that both L10-ordered and (001)-oriented MnAl films were successfully fabricated. The peak intensity of L10-MnAl was improved with increasing both substrate and annealing temperature. However, surface roughness drastically increased above Ts=3000C. We systematically investigated annealing temperature dependence of magnetic properties in MnAl films prepared with Ts = 2500C. As a result, Ku showed a maximum at Ta = 3500C as shown in Fig. 1, and finally obtained a L10-ordered MnAl film with high Ku of 13.0 Merg/cc, relatively low Msof 497 emu/cc and small roughness (Ra) of 0.3 nm in the condition of Ts= 2500C and Ta=3500C. The optimized MnAl film will be greatly useful to realize the high-density STT-MRAM.