FePt基薄膜的结构与磁性
摘要
具有面心四方结构的L10有序化FePt合金具有极高的单轴磁晶各向异性能Ku(-7×107erg/cc),并且化学性质稳定,在开发高密度垂直磁记录介质、垂直磁性隧道结等方面具有潜在的应用前景。应用中,自然生长的磁性颗粒存在颗粒尺寸不均、形状不规则及排列无序等问题。用微加工法制做人工阵列是解决问题的途径之一,但前提是要获得优质连续的薄膜。FePt合金形成L10相需要高温热处理,往往会破坏薄膜的连续。本文通过控制生长条件和热处理环境制备出高质量的连续L10-FePt薄膜。磁力显微镜已经成为获取亚微米尺度微粒子内部磁畴结构信息的有力工具。本文研究了FePt合金用于制作磁力显微镜的高性能磁各向同性探针所需要的Fe、Pt最佳原子比。在FePt合金中掺入少量Ag,有利于降低形成Z10-FePt合金的有序化温度。但是有关相分离的研究,还不充分。本文在FePt中掺入大量的Ag,形成FePt-Ag多层膜,经过高温热处理后,分析样品在磁性、表面形貌、晶体结构等方面的性质。
用磁控溅射法在加热到400℃的MgO(001)单晶基片上沉积了总厚度为25 nm的[Fe(0.6nm)/Fe30.5Pt69.5(1.9 nm)]10多层连续薄膜,总成分配比为Fe50Pt50。然后对其在[500,900]℃温度范围进行真空热处理,分析了热处理温度对薄膜表面形貌、晶体结构以及磁特性的影响。结果表明,在加热基片上生长的FePt薄膜,层间已经发生扩散,但形成的是无序的Al相。经过700℃以上的高温热处理,薄膜转变为具有(001)织构的L10相,易磁化轴沿垂直于膜面的方向,有序度大于0.85,单轴磁晶各向异性能约2.7×107 erg/cc。利用扩散后残存的周期性微弱成分起伏,可以使薄膜在800℃以下保持形貌连续。用原子力显微镜对薄膜表面进行观察证实,在780℃进行热处理,薄膜的表面最平整。这种优质的连续薄膜可以应用于微加工制作超高密度垂直磁记录阵列介质。
用电子束蒸发沉积法在加热到100℃的MgO(001)基板上生长了50 nm厚的FexPt100-x取向薄膜,原子比成分范围为x=[10,85]。在500℃进行保温2 h的原位热处理后,分析样品的结构和沿不同晶向施加磁场时的磁性行为。结果表明,随着x的增加,易磁化轴的方向在沿平行于膜面方向和垂直于膜面方向之间反复变化,取决于内秉的磁晶各向异性与外秉的形状各向异性之间的竞争。当x=60时,由于薄膜发生不完全的A1→L10相转变,形成了A1软磁相与L10硬磁相的复合体,样品沿平行和垂直于膜面方向磁化的矫顽力都达到5 kOe以上沿膜面方向磁化时,矫顽力高于软磁相的磁晶各向异性场,并且正负向磁化的剩余磁化强度明显不相等。采用三磁畴软磁相模型,结合硬磁／软磁交换耦合作用,对此进行了解释。这种硬磁／软磁复合材料适合于用来制作磁力显微镜的各向同性高矫顽力探针。
用磁控溅射法在加热到100℃的石英基片上依次沉积5 nm的MgO下底层和[FePt(dnm)/Ag(3 nm)]n多层膜,d=1,2,3,4；n=9,5,3,2；d×n≈9.对样品在600℃进行30 min的热处理后,所有样品的面内和垂直矫顽力均在10 kOe左右。MgO下底层能够诱导FePt取向生长,形成(001)织构和(100)织构共存的L10相。当d≤2时,薄膜发生明显的相分离。相分离有助于减小FePt颗粒的尺寸。
Due to its extremely large uniaxial magnetic anisotropy (Ku=～7×10-7ergs/cc), small grain size and high chemical stability, the L10-FePt film with face-centered tetragonal (001) texture has attracted great attention for the potential application in perpendicular recording media and magnetic tunnel junction. However, a subsequent anneal to form the L10 phase often result in undesirable dispersive grain size, irregular grain shape and random grain alignment. In this thesis, a kind of heat resisting continuous L10-FePt films suitable for microfabrication of arrays and a kind of hard/soft magnetic FexPt100-x composite with potential application to manufacture the cantilever for magnetic force microscope with high isotropic coercivity were prepared. The phase separation in FePt-Ag nanocomposites was also researched to understand the effect on the morphology. The surface morphology, magnetic properties and lattice structure were anylized.
By magnetron sputtering, [Fe(0.6 nm)/Fe3o.5Pt69.5(1.9 nm)]10 continuous multilayer films with nominal composition of Fe5oPt5o and total thickness of 25 nm were deposited on MgO(001) substrates heated to 400℃, and then subjected to a vacuum annealing at temperatures in the range of Ta=[500,900]℃. The morphology, crystallography as well as magnetic property dependences of Ta were investigated by scanning electron microscope, atomic force microscope, X-ray diffraction and vibrating sample magnetometer. Heating the substrate during sputtering resulted in interlayer diffusion, and the as-deposited multilayer film showed the soft magnetic behaviors of FePt alloy with disordered A1 phase. Annealed at Ta％≥700℃, the film became the ordered L10 phase with significant (001) orientation; the ordering parameter was more than 0.85; the magnetocrystalline anisotropic energy exceeded 2.7×107 erg/cc. Due to the residual subtle periodical compositional fluctuation in the film, the ordering could nucleate interior the film and the Pt-enrichment boundaries were sufficiently suppressed. The continuity of morphology maintained at Ta≤800℃. The observation by atomic force microscope indicated that the film annealed at Ta=780℃had the flattest surface with sparse swells lower than 3 nm. This kind of heat-resisting continuous film would fit the need for microfabrication of patterned arrays of L10 FePt for applications such as the perpendicular magnetic recording media.
FexPt100-x films (50 nm thick) with x=[10,85] in atomic percent were deposited by electron beam onto MgO (001) substrates heated to 100℃. And then the samples were annealed at 500℃ for 2 h. The crystalline structures and anisotropic magnetic properties were investigated. The direction of easy magnetization axis switches between horizontal direction and vertical direction with the increase of x, inducted by the intrinsic magnetocrystalline anisotropy and extrinsic shape anisotropy. At x=60, a composite of disordered A1 phase and ordered L10 phase can be obtained due to the unfinished A1→L10 transformation. Both the horizontal coercivity and the vertical coercivity exceed 5 kOe. The horizontal coercivity is higher than the magnetocrystalline anisotropic field of soft A1 phase, and the horizontal coercive loop is asymmetric. The mechanism is discussed by a tri-domain model for the hard-soft exchange coupling system. This kind of hard/soft magnetic composite has the potential application to manufacture the cantilever for magnetic force microscope with high isotropic coercivity.
By magnetron sputtering, MgO (5 nm) underlayer and [(FePt(d nm)/Ag(3 nm)]n multilayer (d= 1,2,3,4; n= 9,5,3,2; the total thick of FePt film was d×n≈9; the total thick of Ag was 3n) were subsequently deposited onto quartz substrate heated to 100℃, and subjected to an anneal at 600℃for 30 min in vacuum. The vertical and horizontal coercivity is approximately 10 kOe, and the overlap of (002) peak and (200) peak is appeared in all samples. The addition of Ag can prevent the formation of L10-FePt, despite the fact that the MgO underlayer could induce the growth of (001) orientation. The film was phase-separated abruptly at d≤2. The phase separation significantly reduced the size of FePt grain. The Ag addition can decrease the exchange-coupling interaction among FePt grains.
用磁控溅射法在加热到400℃的MgO(001)单晶基片上沉积了总厚度为25 nm的[Fe(0.6nm)/Fe30.5Pt69.5(1.9 nm)]10多层连续薄膜,总成分配比为Fe50Pt50。然后对其在[500,900]℃温度范围进行真空热处理,分析了热处理温度对薄膜表面形貌、晶体结构以及磁特性的影响。结果表明,在加热基片上生长的FePt薄膜,层间已经发生扩散,但形成的是无序的Al相。经过700℃以上的高温热处理,薄膜转变为具有(001)织构的L10相,易磁化轴沿垂直于膜面的方向,有序度大于0.85,单轴磁晶各向异性能约2.7×107 erg/cc。利用扩散后残存的周期性微弱成分起伏,可以使薄膜在800℃以下保持形貌连续。用原子力显微镜对薄膜表面进行观察证实,在780℃进行热处理,薄膜的表面最平整。这种优质的连续薄膜可以应用于微加工制作超高密度垂直磁记录阵列介质。
用电子束蒸发沉积法在加热到100℃的MgO(001)基板上生长了50 nm厚的FexPt100-x取向薄膜,原子比成分范围为x=[10,85]。在500℃进行保温2 h的原位热处理后,分析样品的结构和沿不同晶向施加磁场时的磁性行为。结果表明,随着x的增加,易磁化轴的方向在沿平行于膜面方向和垂直于膜面方向之间反复变化,取决于内秉的磁晶各向异性与外秉的形状各向异性之间的竞争。当x=60时,由于薄膜发生不完全的A1→L10相转变,形成了A1软磁相与L10硬磁相的复合体,样品沿平行和垂直于膜面方向磁化的矫顽力都达到5 kOe以上沿膜面方向磁化时,矫顽力高于软磁相的磁晶各向异性场,并且正负向磁化的剩余磁化强度明显不相等。采用三磁畴软磁相模型,结合硬磁／软磁交换耦合作用,对此进行了解释。这种硬磁／软磁复合材料适合于用来制作磁力显微镜的各向同性高矫顽力探针。
用磁控溅射法在加热到100℃的石英基片上依次沉积5 nm的MgO下底层和[FePt(dnm)/Ag(3 nm)]n多层膜,d=1,2,3,4；n=9,5,3,2；d×n≈9.对样品在600℃进行30 min的热处理后,所有样品的面内和垂直矫顽力均在10 kOe左右。MgO下底层能够诱导FePt取向生长,形成(001)织构和(100)织构共存的L10相。当d≤2时,薄膜发生明显的相分离。相分离有助于减小FePt颗粒的尺寸。
Due to its extremely large uniaxial magnetic anisotropy (Ku=～7×10-7ergs/cc), small grain size and high chemical stability, the L10-FePt film with face-centered tetragonal (001) texture has attracted great attention for the potential application in perpendicular recording media and magnetic tunnel junction. However, a subsequent anneal to form the L10 phase often result in undesirable dispersive grain size, irregular grain shape and random grain alignment. In this thesis, a kind of heat resisting continuous L10-FePt films suitable for microfabrication of arrays and a kind of hard/soft magnetic FexPt100-x composite with potential application to manufacture the cantilever for magnetic force microscope with high isotropic coercivity were prepared. The phase separation in FePt-Ag nanocomposites was also researched to understand the effect on the morphology. The surface morphology, magnetic properties and lattice structure were anylized.
By magnetron sputtering, [Fe(0.6 nm)/Fe3o.5Pt69.5(1.9 nm)]10 continuous multilayer films with nominal composition of Fe5oPt5o and total thickness of 25 nm were deposited on MgO(001) substrates heated to 400℃, and then subjected to a vacuum annealing at temperatures in the range of Ta=[500,900]℃. The morphology, crystallography as well as magnetic property dependences of Ta were investigated by scanning electron microscope, atomic force microscope, X-ray diffraction and vibrating sample magnetometer. Heating the substrate during sputtering resulted in interlayer diffusion, and the as-deposited multilayer film showed the soft magnetic behaviors of FePt alloy with disordered A1 phase. Annealed at Ta％≥700℃, the film became the ordered L10 phase with significant (001) orientation; the ordering parameter was more than 0.85; the magnetocrystalline anisotropic energy exceeded 2.7×107 erg/cc. Due to the residual subtle periodical compositional fluctuation in the film, the ordering could nucleate interior the film and the Pt-enrichment boundaries were sufficiently suppressed. The continuity of morphology maintained at Ta≤800℃. The observation by atomic force microscope indicated that the film annealed at Ta=780℃had the flattest surface with sparse swells lower than 3 nm. This kind of heat-resisting continuous film would fit the need for microfabrication of patterned arrays of L10 FePt for applications such as the perpendicular magnetic recording media.
FexPt100-x films (50 nm thick) with x=[10,85] in atomic percent were deposited by electron beam onto MgO (001) substrates heated to 100℃. And then the samples were annealed at 500℃ for 2 h. The crystalline structures and anisotropic magnetic properties were investigated. The direction of easy magnetization axis switches between horizontal direction and vertical direction with the increase of x, inducted by the intrinsic magnetocrystalline anisotropy and extrinsic shape anisotropy. At x=60, a composite of disordered A1 phase and ordered L10 phase can be obtained due to the unfinished A1→L10 transformation. Both the horizontal coercivity and the vertical coercivity exceed 5 kOe. The horizontal coercivity is higher than the magnetocrystalline anisotropic field of soft A1 phase, and the horizontal coercive loop is asymmetric. The mechanism is discussed by a tri-domain model for the hard-soft exchange coupling system. This kind of hard/soft magnetic composite has the potential application to manufacture the cantilever for magnetic force microscope with high isotropic coercivity.
By magnetron sputtering, MgO (5 nm) underlayer and [(FePt(d nm)/Ag(3 nm)]n multilayer (d= 1,2,3,4; n= 9,5,3,2; the total thick of FePt film was d×n≈9; the total thick of Ag was 3n) were subsequently deposited onto quartz substrate heated to 100℃, and subjected to an anneal at 600℃for 30 min in vacuum. The vertical and horizontal coercivity is approximately 10 kOe, and the overlap of (002) peak and (200) peak is appeared in all samples. The addition of Ag can prevent the formation of L10-FePt, despite the fact that the MgO underlayer could induce the growth of (001) orientation. The film was phase-separated abruptly at d≤2. The phase separation significantly reduced the size of FePt grain. The Ag addition can decrease the exchange-coupling interaction among FePt grains.
引文
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