于广华
侧重在纳米尺度上研究薄膜材料制备、以及薄膜材料界面的微结构与材料性能的关系;研究磁电阻薄膜材料及其在高灵敏度磁传感器中的应用。
个性化签名
- 姓名:于广华
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学术头衔:
博士生导师
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学科领域:
材料科学基础学科
- 研究兴趣:侧重在纳米尺度上研究薄膜材料制备、以及薄膜材料界面的微结构与材料性能的关系;研究磁电阻薄膜材料及其在高灵敏度磁传感器中的应用。
于广华教授,博士,毕业于北京科技大学材料物理与化学系。北京科技大学现代物理研究中心副主任,中国金属学会材料科学分会表面与界面学术委员会副主任。2003年9月至2004年3月曾到Max Plank Institute of Microstructure Physics访问研究。侧重在纳米尺度上研究薄膜材料制备、以及薄膜材料界面的微结构与材料性能的关系;研究磁电阻薄膜材料及其在高灵敏度磁传感器中的应用。已发表学术论文70多篇, 被SCI网络版(SCI-EXPANDED)收录45篇,在SCI网络版中被引用105次。发明专利五项,2001--2003连续两年度以第一作者发表的《SCIE》科研论文排全校第二。作为骨干曾参加了"八五" 环境断裂机理和"九五"巨磁电阻薄膜材料等国家自然科学基金重大课题的研究。目前,主持多项国家自然科学基金、北京市自然科学基金和教育部博士点基金等基金项目;还主持国家高技术研究发展计划"863计划"、教育部重点项目、军工项目以及"863"配套项目等属于应用技术开发方面的项目。
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【期刊论文】Effect of Ta on magnetic thicknesses of permalloy (Ni81Fe19) films
于广华 , GHYu, , T Yang, F W Zhu, M H Li, and W Y Lai
J. Phys. D: Appl. Phys. 36(2003)4-8,-0001,():
-1年11月30日
Effect of Ta and Cu seed layers, as well as Ta and Cu cap layers on the effective magnetic thickness of ultrathin permalloy (Ni81Fe19) were experimentally investigated for magnetic random access memory applications. The films were deposited by magnetron sputtering. For a Ta/Ni81Fe19/Ta fundamental structure, Ta seed and Ta cap layers resulted in a loss of moment equivalent to a magnetically dead layer of thickness 1.6
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于广华 , M. H. Li a) and G. H. Yu, H. W. Jiang, J. W. Cai and W. Y. Lai, F. W. Zhu
J. Appl. Phys., Vol. 92, No.5, 1 September 2002,-0001,():
-1年11月30日
Two sets of NiFe/FeMn films with Ta and Ta/Cu buffer layers were prepared by magnetron sputtering. Results show that the exchange bias field of NiFe/FeMn films with a Ta/Cu buffer is lower than that of the films with a Ta buffer. The crystalline texture, surface roughness, and element distribution of these two sets of samples were examined, and there is no apparent difference for the texture and roughness. However, the segregation of Cu atoms on the surface of NiFe in the trilayer of Ta/Cu/NiFe has been observed by using the angle-resolved x-ray photoelectron spectroscopy. The decrease of the exchange bias field for NiFe/FeMn films with a Ta/Cu buffer layers is mainly caused by the segragation of Cu atoms to the surface of the NiFe layer
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于广华 , G. H. Yu, a), M. H. Li, F. W. Zhu, Q. K. Li, and Y. Zhang, C. L. Chai, H. W. Jiang and W. Y. Lai
J. Appl. Phys., Vol. 91, No.6, 15 March 2002,-0001,():
-1年11月30日
Experimental results show that the exchange coupling field (Hex) of NiFe/FeMn for Ta/NiFe/FeMn/Ta multilayers is higher than that for spin-valve multilayers Ta/NiFe/Cu/NiFe/FeMn/Ta. In order to find out the reason, the composition and chemical states at the surface of Ta (12nm)/NiFe(7nm), Ta (12 nm)/NiFe(7nm)/Cu(4nm), and Ta (12nm)/NiFe(7nm)/Cu(3nm)/NiFe(5nm) were studied using x-ray photoelectron spectroscopy. The results show that no elements from lower layers float out or segregate to the surface in the first and second samples. However, Cu atoms segregate to the surface of Ta (12nm)/NiFe(7nm)/Cu(3nm)/NiFe(5nm) multilayers, i.e., Cu atoms segregate to the NiFe/FeMn interface for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers.We believe that the presence of Cu atoms at the interface of NiFe/FeMn is one of the important factors which causes the exchange coupling field (Hex) of Ta/NiFe/Cu/NiFe/FeMn/Ta to be weaker than that of Ta/NiFe/FeMn/Ta.
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【期刊论文】Magnetic properties and x-ray photoelectron spectroscopy study of NiO
于广华 , G. H. Yu a), and L. R. Zeng, F. W. Zhu, C. L. Chai, W. Y. Lai
J. Appl. Phys., Vol. 90, No.8, 15 October 2001,-0001,():
-1年11月30日
Ta/NiOx/Ni81Fe19/Ta multilayers were prepared by rf reactive and dc magnetron sputtering. The exchange-coupling field (Hex) and the coercivity (Hc) of NiOx/Ni81Fe19 as a function of the ratio of Ar to O2 during the deposition process were studied. The composition and chemical states at the interface region of NiOx/NiFe were also investigated using the x-ray photoelectron spectroscopy (XPS) and peak decomposition technique. The results show that the ratio of Ar to O2 has a great effect on the nickel chemical states in NiOx film. When the ratio of Ar to O2 is equal to 7 and the argon sputtering pressure is 0.57 Pa, the x value is approximately 1 and the valence of nickel is +2. At this point, NiOx is antiferromagnetic NiO and the corresponding Hex is the largest. As the ratio of Ar/O2 deviates from 7, the exchange-coupling field (Hex) will decrease due to the presence of magnetic defects such as Ni+3 or metallic Ni at the interface region of NiOx/NiFe, while the coercivity (Hc) will increase due to the metallic Ni. XPS studies also show that there are two thermodynamically favorable reactions at the NiO/NiFe interface: NiO+Fe=Ni+FeO and 3NiO+2Fe=3Ni+Fe2O3. These interface reaction products are magnetic defects at the interface region of NiO/NiFe, it is believed that these magnetic defects would have an effect on the exchange-coupling field (Hex) and the coercivity (Hc) of NiO/NiFe.
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【期刊论文】Interface reaction of Ta/NiO and its e!ect on exchange coupling
于广华 , G.H. Yu*, C.L. Chai, H.C. Zhao, F.W. Zhu, J.M. Xiao
Journal of Magnetism and Magnetic Materials 224(2001)61-64,-0001,():
-1年11月30日
Ta/NiO/NiFe/Ta multilayers, utilizing Ta as the bu!er layer, were prepared by RF reactive and DC magnetron sputtering. The exchange coupling field between NiO and NiFe reached a maximum value of 120Oe at a NiO film thickness of 50nm. The composition and chemical state at the interface region of Ta/NiO/Ta were studied using the X-ray photoelectron spectroscopy (XPS) and peak decomposition technique. The results show that there is an &intermixing layer'at the Ta/NiO (and NiO/Ta) interface due to a thermodynamically favorable reaction: 2Ta+5NiO=5Ni+Ta2O5. This interface reaction has an effect on the exchange coupling. The thickness of the &intermixing layer' as estimated by XPS depth-profiles was about 8-10nm.
Interface reaction, X-ray photoelectron spectroscopy, Exchange coupling, Spin-valve multilayer
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于广华 , B. Dai, J. W. Cai, a), W. Y. Lai, F. Shen, and Z. Zhang, G. H. Yu
Appl. Phys. Lett., Vol. 82, No.21, 26 May 2003,-0001,():
-1年11月30日
We investigated the magnetic properties of sputtered Ni0.8Fe0.2/Ni1-xMnx (0.43≤x≤0.70) bilayers and found that an antiferromagnetic equiatomic NiMn layer could be formed through Mn diffusion with reduced thickness and a much shortened annealing time if the Ni1-xMnx layer is off-stoichiometric with suitable excess Mn. An overdose of Mn in a NiMn precursor layer was demonstrated to enhance the migration and the diffusion of Mn atoms, which seemed to promote the formation of antiferromagnetic NiMn of the θ phase, but in the mean time led to the deterioration of the adjacent ferromagnetic layer. We thus introduced the nano-oxide layer in the ferromagnetic layer near the interface of ferromagnetic and antiferromagnetic layers, which was proven to be very efficient to prevent Mn atoms from further intruding into the ferromagnetic layer even in the case that a large amount of Mn atoms were involved. As a result, a ferromagnetic layer pinned by a NiMn layer with excellent performance has been developed in a much simplified process.
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【期刊论文】A specular spin valve with discontinuous nano-oxide layers
于广华 , F. Shen, Q. Y. Xu, G. H. Yu, a) W. Y. Lai, and Z. Zhang b), Z. Q. Lu c) and G. Pan, Abdul Al-Jibouri
Appl. Phys. Lett., Vol. 80, No.23, 10 June 2002,-0001,():
-1年11月30日
Microstructures of the specular spin valve with two nano-oxide layers (NOL1 and NOL2) have been studied at the atomic level. When the NOLs are incorporated in a bottom-pinned spin valve, a significant enhancement in magnetoresistance ratio with greatly decreased sense-layer thickness is achieved. Cross-sectional high-resolution electron microscopy (HREM) studies show that the NOL1 introduced from oxidation of the original bottom-pinned CoFe layer is actually a mixture of oxides and ferromagnetic metals. No CoFe oxides but Ta2O5 is found over the oxidation-treated CoFe sense layer by HREM and x-ray photoelectron spectroscopy study. The Ta2O5 layer acting as the NOL2 can be interpreted as being formed through a solid-state oxidation reaction between the oxidized CoFe sense layer and the Ta capping layers.
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【期刊论文】Interlayer segregation in magnetic multilayers and its influence on exchange coupling
于广华 , G. H. Yu, a), M. H. Li, and F. W. Zhu, H. W. Jiang and W. Y. Lai, C. L. Chai
Appl. Phys. Lett., Vol. 82, No.1, 6 January 2003,-0001,():
-1年11月30日
Experimental results show that the exchange coupling field (Hex) of NiFe/FeMn for Ta/NiFe/FeMn/Ta multilayers is higher than that for spin-valve multilayers Ta/NiFe/Cu/NiFe/FeMn/Ta. X-ray photoelectron spectroscopy shows that Cu atoms segregate to the NiFe/FeMn interface for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers. While studying Ta/X (X=Bi,Pb,Ag,In)/NiFe/FeMn multilayers, we also find that X atoms segregate to the NiFe/FeMn interface, which results in a decrease of the Hex. However, a small amount of Bi, Pb, etc. deposited between Cu and pinned NiFe layer for Ta/NiFe/Cu/NiFe/FeMn/Ta multilayers can increase Hex.
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【期刊论文】Interface reaction of Ta/Ni81Fe19 or Ni81Fe19/Ta and its suppression
于广华 , G. H. Yu, a), H. C. Zhao, M. H. Li, and F. W. Zhu, W. Y. Lai
Appl. Phys. Lett., Vol. 80, No.3, 21 January 2002,-0001,():
-1年11月30日
Ta/Ni81Fe19 and Ni81Fe19/Ta structures are commonly used in the magnetic multilayers with giant magnetoresistance. For a Ta/Ni81Fe19/Ta fundamental structure, Ta seed and Ta cap layers resulted in a loss of moment equivalent to a magnetically dead layer of thickness 1.6
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【期刊论文】Interface reaction of NiO/NiFe and its influence on magnetic properties
于广华 , G. H. Yu, a), C. L. Chai, F. W. Zhu, and J. M. Xiao, W. Y. Lai
Appl. Phys. Lett., Vol. 78, No.12, 19 March 2001,-0001,():
-1年11月30日
Ta/NiO/NiFe/Ta multilayers were prepared by rf reactive and dc magnetron sputtering. The xchange coupling field between NiO and NiFe reached 120 Oe. The composition and chemical states at the interface region of NiO/NiFe were studied using the x-ray photoelectron spectroscopy (XPS) and peak decomposition technique. The results show that there are two thermodynamically favorable reactions at NiO/NiFe interface: NiO+Fe=Ni+FeO and 3NiO+2Fe=3Ni+Fe2O3. The thickness of the chemical reaction as estimated by angle-resolved XPS was about 1-1.5nm. These nterface reaction products are magnetic defects, and we believe that the exchange coupling field Hex and the coercivity Hc of NiO/NiFe are affected by these defects.
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