高过渡族元素掺杂ZnO基磁性半导体研究
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摘要
作为一种具有丰富物理内涵和重要应用前景的新型电子材料，磁性半导体已成为自旋电子学这个新领域的研究热点。磁性半导体通常是通过掺杂过渡族金属元素TM如V，Cr,Mn，Fe，Co，Ni等进入Ⅲ-Ⅴ族、Ⅱ-Ⅵ族和Ⅳ族化合物或单质，如InAs，GaAs，ZnO，TiO_2，ZnTe，Ge，Si等得到的。目前国际上的研究热点主要集中在寻找具有室温铁磁性的磁性半导体材料并探讨产生铁磁性的根源。在In_(1-x)Mn_xAs和Ga_(1-x)Mn_xAs磁性半导体方面，Ohno等人做了大量开创性的工作，率先发现了铁磁性，但其居里温度太低(目前最高报道为170K)，限制了其在室温的应用。
自从Dietl等人在理论上预言ZnO基磁性半导体的居里温度高于室温，ZnO基磁性半导体就引起了研究者们的广泛关注。到目前为止，虽然人们对磁性半导体的微结构、磁性、电子输运、磁电阻、光学、磁光等性质都作了一些研究，然而来自不同研究组的结果很不一致，甚至互相矛盾。氧化物磁性半导体的磁性起源是争论的焦点。研究者认为磁性可能来源于载流子诱导的交换作用、双交换作用等内禀的机制，也有可能是由铁磁性杂质相引起的，因为过渡元素在半导体中的溶解度普遍比较低，容易形成磁性杂质相。在磁性半导体中，由于s，p载流子与掺杂过渡元素的局域的d电子之间产生交换作用，从而产生的铁磁性称为载流子诱导铁磁性，这种机理成功地解释了(Ga，Mn)As等低居里温度磁性半导体的磁性起源。但是高居里温度氧化物磁性半导体中磁性的起源仍不明确。同时，氧化物磁性半导体中还存在掺杂量较低、饱和磁化强度较低、高温磁电阻很小、输运机理不清楚等诸多问题。本论文工作包括制备Co和Fe掺杂ZnO室温磁性半导体，对其磁性、输运、磁光等性质进行了研究，并对氧化物磁性半导体的磁性起源、输运机理等问题进行了初步探讨，获得了如下有意义的实验结果。
1．我们用交替溅射过渡族元素层与ZnO层的方法制备了高过渡族会属元素含量的ZnO基磁性半导体薄膜。众所周知，过渡族金属元素在氧化物中的溶解度都比较低，因此很难在热力学平衡态下实现氧化物中高浓度掺杂过渡族元素，形成单一相，而不出现像过渡族金属颗粒等这类杂相析出。我们在水冷的玻璃衬底上，交替溅射非常薄的过渡元素层和ZnO层，每一层的厚度大约1-3个原子单层。这样，利用表面的粗糙度和原子间相互扩散，过渡元素与ZnO彼此扩散，形成均一的Zn_(1-x)TM_xO相。所研究的过渡族元素TM包括Co和Fe。X射线衍射和透射电子显微镜等结构测量表明，样品中并没有过渡元素金属相析出，从而解决了ZnO基磁性半导体中高浓度掺杂过渡元素的问题。我们的结果表明，采用这种特殊的交替溅射的镀膜方法，可以得到室温下具有铁磁性的磁性半导体材料，这为磁性半导体的研究提供了一种新的有效的材料制备方法。
2．系统研究了Co-ZnO和Fe-ZnO磁性半导体薄膜，包括制备工艺、后期热处理、材料的结构、磁性、输运特性和磁光效应。结果表明，所获得的薄膜样品具有高的居里温度、高饱和磁化强度，并证明样品为本征的磁性半导体。在Co-ZnO体系中，X射线磁圆二色谱表明ZnO中氧化态的Co处于高自旋态，并对磁性有贡献，同时，结构测量表明样品中并没有其他铁磁性杂相，因而磁性来源于本征的Co-ZnO磁性半导体。磁性测量表明，样品具有室温铁磁性，居里温度高于室温。样品在室温和低温都有很高的饱和磁化强度，典型样品[ZnO0．5nm／Co 0．5nm]_(60)的饱和磁化强度在5K和293K时分别为550 emu／cm~3(1．41μ_B／Co)和400 emu／cm~3(1．03μ_B/Co)。在Fe-ZnO体系中，同样发现了室温铁磁性，并且居里温度高于室温，具有高的饱和磁化强度，典型样品[ZnO 0．16nm／Fe0．48nm]_(30)样品的饱和磁化强度在5K和293K分别为765emu／cm~3(1．44μ_B/Fe)和632emu／cm~3(1．18μ_B/Fe)。
3．用改进的F-center模型解释了磁性半导体的磁性起源。样品中氧空位作为施主缺陷将束缚一个电子，由于电子与磁性离子之间交换作用形成束缚磁极化子，束缚磁极化子之间通过交迭区域的磁性离子相互作用，形成长程的铁磁序。而弱局域的电子随局域长度增加，等效于类氢半径增加，从而提高了材料的居旱温度和饱和磁化强度。用改进的F-center模型可以有效地对Co-ZnO体系的磁性和输运特性的实验结果进行有效的理论解释，说明所得的Co-ZnO体系其磁性来源于本征的Co-ZnO磁性半导体。
4．研究了在ZnO基磁性半导体中的自旋相关电子输运和磁电阻。在Co-ZnO体系里，实验上发现不同样品的lnρ与T~(-1／2)均呈线性关系，并且在不同的磁场下，有不同的斜率和截距；在Fe-ZnO体系里，实验上发现不同成分样品的电阻与温度关系均满足lnρ~∞T_H／T+(T_(ES)／T)~(-1/2)的形式。在Efros变程跃迁导电模型基础上，我们建立了考虑库仑相互作用、载流子之间自旋-自旋交换作用和硬带能的统一模型，成功地解释了ZnO基磁性半导体中观察到的电子输运现象。另外，室温下制备态的ZnO基磁性半导体中还发现了大的负磁电阻，293K时Co-ZnO和Fe-ZnO中磁电阻分别为11％和8％，5K时磁电阻分别为34％和27％。
5．研究了制备态和退火态Co-ZnO磁性半导体的极向克尔谱，发现通过调制成分和退火处理，可以大幅度调制极向克尔谱。退火后样品的磁光克尔旋转角得到显著增强，克尔角最大值达到0．72°，比纯Co薄膜、Pt／Co多层膜和Pt_xCo_(1-x)合金的克尔角都要大。我们认为这是由于退火后样品变成了Co颗粒和Co-ZnO磁性半导体的纳米复合体系。在磁性半导体中得到如此大的室温磁光效应，到目前为至还未见其它研究组报道。
6．用铁磁共振研究了Fe-ZnO磁性半导体。我们通过研究共振场随磁场的变化关系，得到了有效g因子、各向异性场等磁参量。随Fe成分增加，样品饱和磁矩增加，垂直模式共振场增加。铁磁共振峰线宽随Fe成分增加而减小，表明样品中化学成分非均匀性随之减小。结果表明，适当增加过渡元素掺杂量将有利于提高磁性半导体室温饱和磁矩。
Recently, magnetic semiconductors (MS) have attracted considerable attention because of their potential applications in spintronics devices. Magnetic semiconductors are usually synthesized by doping transitional metal elements such as V, Cr, Mn, Fe, Co, and Ni, intoⅢ-Ⅴ,Ⅱ-Ⅵ, andⅣgroup compounds such as InAs, GaAs, ZnO, TiO_2, SnO_2, ZnTe, etc. In_(1-x)Mn_xAs and Ga_(1-x)Mn_xAs are pioneering examples of such magnetic semiconductors with ferromagnetism, but the Curie temperature is too low (The obtained highest Curie temperature in Ga_(1-x)Mn_xAs is 170 K, still far below the room temperature).
ZnO-based MS are paid much attention since the theoretical prediction of room temperature ferromagnetism on ZnO- and GaN-based MS. But reported experimental results of ZnO-based magnetic semiconductors by different research groups are quite different and even contradictory, and hence the origin of the ferromagnetism is still an open question from the experimental point of view. Besides some intrinsic origins for ferromagnetism, such as carrier-mediated interaction, super-exchange interaction, ferromagnetism from secondary phases was also supposed due to the low solubility of transition metal elements in the host lattice. In the magnetic semiconductor system, due to the interactions between the s, p electrons of the carriers and the localized d electrons of the doped transitional metal elements, the ferromagnetism can be established, which is regarded as the carrier-mediated ferromagnetism. But the detailed mechanisms of the ferromagnetism of high Curie temperature are still not well understood theoretically. In this thesis, I mainly introduce our recent work about the properties of Co and Fe doped ZnO magnetic semiconductors with room temperature ferromagnetism.
1. ZnO-based magnetic semiconductor films with high concentration of the transitional metal elements were prepared by alternately sputtering very thin transitional metal (TM) and ZnO layers. It is well known that the transition metals usually have very low solubility in oxides, such as ZnO, TiO_2, SnO_2,In_2O_3 and so on. Therefore, it is not possible for high concentration doping of TM elements into these oxides in the thermal equilibrium state to form a single phase, such as Zn_(1-x)Co_xO, without precipitation phases like Co metal clusters. We alternately deposited very thin TM and ZnO layers, such as only 1-3 atomic monolayers, on the water cooled glass substrates. Since the interface roughness and the interdiffusion length are comparable, TM and ZnO may incorporate into each other due to interdiffusion to form Zn_(1-x)TM_xO phase. X-ray diffraction and transmission electron microscopy didn't find any TM metal clusters in the as-deposited Co-ZnO and Fe-ZnO magnetic semiconductor films.
2. Co-ZnO as-deposited samples have been proved to be intrinsic magnetic semiconductor with high Curie temperature and high magnetization. The magnetic measurements showed that the samples are ferromagnetic at room temperature and the Curie temperature is above the room temperature. The saturation magnetizations of a typical sample [ZnO 0.5nm/Co 0.5nm]_(60) are very high at both 5 K (550 emu/cm~3(1.41μ_B/Co))and 290 K (400 emu/cm~3(1.03μ_B/Co)), respectively. X-ray magnetic circular dichroism results indicated that the oxidation valence state of Co in high spin state in the host ZnO has contribution to the magnetism, and the impurity phases are excluded by structural measurements. Therefore the origin of magnetisim of Co-ZnO as-deposited samples is suggested to be intrinsic.
3.The spin-dependent electrical transport and magnetoresistance in ZnO-based magnetic semiconductors have been studied experimentally andtheoretically. In Co-ZnO magnetic semiconductors a linear relation of lnρversusT~(1/2), which shows different slopes and intersections at different magnetic fields, is observed experimentally in the low temperature range. In Fe-ZnO magnetic semiconductors, a universal form of the resistance versus temperature, i.e.,lnρ~∞T_H /T + (T_(ES)/T)~(-1 2), is observed experimentally at different magnetic fields. The spin-dependent variable hopping model has been proposed by taking into account the electron-electron Coulomb interaction, the spin-spin exchange interaction and hard gap energy in the same frame, which can well described the observed magnetic transport properties in both Co-ZnO and Fe-ZnO magnetic semiconductor systems. Moreover, large negative magnetoresistance is observed at room temperature in ZnO-based magnetic semiconductors and the negative magnetoresistances are about 11% and 8% at 293K and 34% and 27% at 5K in Co-ZnO and Fe-ZnO magnetic semiconductors, respectively.
4.The ferromagnetism of ZnO-based magnetic semiconductors is explained by the modified scenario of the F-center mediated ferromagnetism. The oxygen vacancies are easily fromed in ZnO material. The oxygen vacanciy acts as a shallow doner in Co doped ZnO and traps an electron. Cansidering the interaction of the magnetic cations with the trapped hydrogenic electron in the impurity band, the trapped electrons tend to form bound magnetic polarons, coupling the 3d moments of the ions within their orbits. The interaction between the bound magnetic polarons by means of the shared impurity cations may be ferromagnetic at large concentrations of magnetic impurities. The strong interaction between the weakly localized s,p electrons of the oxygen vacancies and the strong localized d electrons of the Co may enhance the Curie temperature and saturation magnetization.
5.The polar Kerr rotation and ellipticity spectra of the as-deposited and annealed Co-ZnO magnetic semiconductors were studied. The Kerr rotation spectra versus the photon energy can be greatly modulated by adjusting the Co concentrationor annealing the samples. Moreover, the observed maximal Kerr rotation, 0.72°in anannealed sample is higher than those of pure Co films, Pt/Co multilayers and Pt_xCo_(1-x) alloys. The enhanced Kerr rotation in the annealed samples can be explained by the fact that the annealed samples became a nanocomposite system consisting of Co clusters and Co-ZnO magnetic semiconductor.
6. Ferromagnetic resonance is used to study Fe-ZnO magnetic semiconductors. The angular dependence of ferromagnetic resonance field for the samples with different compositions was studied. As the Fe content increases, the saturation magnetization increases, and the resonance field in normal resonance mode increases. The linewidth of the ferromagnetic resonance reduces as the Fe content increases, indicating that the inhomogeneity in chemical composition reduces with increasing Fe content. Therefore, suitably increasing Fe content is favorable to obtain magnetic semiconductor films with high saturation magnetization at room temperature.
自从Dietl等人在理论上预言ZnO基磁性半导体的居里温度高于室温，ZnO基磁性半导体就引起了研究者们的广泛关注。到目前为止，虽然人们对磁性半导体的微结构、磁性、电子输运、磁电阻、光学、磁光等性质都作了一些研究，然而来自不同研究组的结果很不一致，甚至互相矛盾。氧化物磁性半导体的磁性起源是争论的焦点。研究者认为磁性可能来源于载流子诱导的交换作用、双交换作用等内禀的机制，也有可能是由铁磁性杂质相引起的，因为过渡元素在半导体中的溶解度普遍比较低，容易形成磁性杂质相。在磁性半导体中，由于s，p载流子与掺杂过渡元素的局域的d电子之间产生交换作用，从而产生的铁磁性称为载流子诱导铁磁性，这种机理成功地解释了(Ga，Mn)As等低居里温度磁性半导体的磁性起源。但是高居里温度氧化物磁性半导体中磁性的起源仍不明确。同时，氧化物磁性半导体中还存在掺杂量较低、饱和磁化强度较低、高温磁电阻很小、输运机理不清楚等诸多问题。本论文工作包括制备Co和Fe掺杂ZnO室温磁性半导体，对其磁性、输运、磁光等性质进行了研究，并对氧化物磁性半导体的磁性起源、输运机理等问题进行了初步探讨，获得了如下有意义的实验结果。
1．我们用交替溅射过渡族元素层与ZnO层的方法制备了高过渡族会属元素含量的ZnO基磁性半导体薄膜。众所周知，过渡族金属元素在氧化物中的溶解度都比较低，因此很难在热力学平衡态下实现氧化物中高浓度掺杂过渡族元素，形成单一相，而不出现像过渡族金属颗粒等这类杂相析出。我们在水冷的玻璃衬底上，交替溅射非常薄的过渡元素层和ZnO层，每一层的厚度大约1-3个原子单层。这样，利用表面的粗糙度和原子间相互扩散，过渡元素与ZnO彼此扩散，形成均一的Zn_(1-x)TM_xO相。所研究的过渡族元素TM包括Co和Fe。X射线衍射和透射电子显微镜等结构测量表明，样品中并没有过渡元素金属相析出，从而解决了ZnO基磁性半导体中高浓度掺杂过渡元素的问题。我们的结果表明，采用这种特殊的交替溅射的镀膜方法，可以得到室温下具有铁磁性的磁性半导体材料，这为磁性半导体的研究提供了一种新的有效的材料制备方法。
2．系统研究了Co-ZnO和Fe-ZnO磁性半导体薄膜，包括制备工艺、后期热处理、材料的结构、磁性、输运特性和磁光效应。结果表明，所获得的薄膜样品具有高的居里温度、高饱和磁化强度，并证明样品为本征的磁性半导体。在Co-ZnO体系中，X射线磁圆二色谱表明ZnO中氧化态的Co处于高自旋态，并对磁性有贡献，同时，结构测量表明样品中并没有其他铁磁性杂相，因而磁性来源于本征的Co-ZnO磁性半导体。磁性测量表明，样品具有室温铁磁性，居里温度高于室温。样品在室温和低温都有很高的饱和磁化强度，典型样品[ZnO0．5nm／Co 0．5nm]_(60)的饱和磁化强度在5K和293K时分别为550 emu／cm~3(1．41μ_B／Co)和400 emu／cm~3(1．03μ_B/Co)。在Fe-ZnO体系中，同样发现了室温铁磁性，并且居里温度高于室温，具有高的饱和磁化强度，典型样品[ZnO 0．16nm／Fe0．48nm]_(30)样品的饱和磁化强度在5K和293K分别为765emu／cm~3(1．44μ_B/Fe)和632emu／cm~3(1．18μ_B/Fe)。
3．用改进的F-center模型解释了磁性半导体的磁性起源。样品中氧空位作为施主缺陷将束缚一个电子，由于电子与磁性离子之间交换作用形成束缚磁极化子，束缚磁极化子之间通过交迭区域的磁性离子相互作用，形成长程的铁磁序。而弱局域的电子随局域长度增加，等效于类氢半径增加，从而提高了材料的居旱温度和饱和磁化强度。用改进的F-center模型可以有效地对Co-ZnO体系的磁性和输运特性的实验结果进行有效的理论解释，说明所得的Co-ZnO体系其磁性来源于本征的Co-ZnO磁性半导体。
4．研究了在ZnO基磁性半导体中的自旋相关电子输运和磁电阻。在Co-ZnO体系里，实验上发现不同样品的lnρ与T~(-1／2)均呈线性关系，并且在不同的磁场下，有不同的斜率和截距；在Fe-ZnO体系里，实验上发现不同成分样品的电阻与温度关系均满足lnρ~∞T_H／T+(T_(ES)／T)~(-1/2)的形式。在Efros变程跃迁导电模型基础上，我们建立了考虑库仑相互作用、载流子之间自旋-自旋交换作用和硬带能的统一模型，成功地解释了ZnO基磁性半导体中观察到的电子输运现象。另外，室温下制备态的ZnO基磁性半导体中还发现了大的负磁电阻，293K时Co-ZnO和Fe-ZnO中磁电阻分别为11％和8％，5K时磁电阻分别为34％和27％。
5．研究了制备态和退火态Co-ZnO磁性半导体的极向克尔谱，发现通过调制成分和退火处理，可以大幅度调制极向克尔谱。退火后样品的磁光克尔旋转角得到显著增强，克尔角最大值达到0．72°，比纯Co薄膜、Pt／Co多层膜和Pt_xCo_(1-x)合金的克尔角都要大。我们认为这是由于退火后样品变成了Co颗粒和Co-ZnO磁性半导体的纳米复合体系。在磁性半导体中得到如此大的室温磁光效应，到目前为至还未见其它研究组报道。
6．用铁磁共振研究了Fe-ZnO磁性半导体。我们通过研究共振场随磁场的变化关系，得到了有效g因子、各向异性场等磁参量。随Fe成分增加，样品饱和磁矩增加，垂直模式共振场增加。铁磁共振峰线宽随Fe成分增加而减小，表明样品中化学成分非均匀性随之减小。结果表明，适当增加过渡元素掺杂量将有利于提高磁性半导体室温饱和磁矩。
Recently, magnetic semiconductors (MS) have attracted considerable attention because of their potential applications in spintronics devices. Magnetic semiconductors are usually synthesized by doping transitional metal elements such as V, Cr, Mn, Fe, Co, and Ni, intoⅢ-Ⅴ,Ⅱ-Ⅵ, andⅣgroup compounds such as InAs, GaAs, ZnO, TiO_2, SnO_2, ZnTe, etc. In_(1-x)Mn_xAs and Ga_(1-x)Mn_xAs are pioneering examples of such magnetic semiconductors with ferromagnetism, but the Curie temperature is too low (The obtained highest Curie temperature in Ga_(1-x)Mn_xAs is 170 K, still far below the room temperature).
ZnO-based MS are paid much attention since the theoretical prediction of room temperature ferromagnetism on ZnO- and GaN-based MS. But reported experimental results of ZnO-based magnetic semiconductors by different research groups are quite different and even contradictory, and hence the origin of the ferromagnetism is still an open question from the experimental point of view. Besides some intrinsic origins for ferromagnetism, such as carrier-mediated interaction, super-exchange interaction, ferromagnetism from secondary phases was also supposed due to the low solubility of transition metal elements in the host lattice. In the magnetic semiconductor system, due to the interactions between the s, p electrons of the carriers and the localized d electrons of the doped transitional metal elements, the ferromagnetism can be established, which is regarded as the carrier-mediated ferromagnetism. But the detailed mechanisms of the ferromagnetism of high Curie temperature are still not well understood theoretically. In this thesis, I mainly introduce our recent work about the properties of Co and Fe doped ZnO magnetic semiconductors with room temperature ferromagnetism.
1. ZnO-based magnetic semiconductor films with high concentration of the transitional metal elements were prepared by alternately sputtering very thin transitional metal (TM) and ZnO layers. It is well known that the transition metals usually have very low solubility in oxides, such as ZnO, TiO_2, SnO_2,In_2O_3 and so on. Therefore, it is not possible for high concentration doping of TM elements into these oxides in the thermal equilibrium state to form a single phase, such as Zn_(1-x)Co_xO, without precipitation phases like Co metal clusters. We alternately deposited very thin TM and ZnO layers, such as only 1-3 atomic monolayers, on the water cooled glass substrates. Since the interface roughness and the interdiffusion length are comparable, TM and ZnO may incorporate into each other due to interdiffusion to form Zn_(1-x)TM_xO phase. X-ray diffraction and transmission electron microscopy didn't find any TM metal clusters in the as-deposited Co-ZnO and Fe-ZnO magnetic semiconductor films.
2. Co-ZnO as-deposited samples have been proved to be intrinsic magnetic semiconductor with high Curie temperature and high magnetization. The magnetic measurements showed that the samples are ferromagnetic at room temperature and the Curie temperature is above the room temperature. The saturation magnetizations of a typical sample [ZnO 0.5nm/Co 0.5nm]_(60) are very high at both 5 K (550 emu/cm~3(1.41μ_B/Co))and 290 K (400 emu/cm~3(1.03μ_B/Co)), respectively. X-ray magnetic circular dichroism results indicated that the oxidation valence state of Co in high spin state in the host ZnO has contribution to the magnetism, and the impurity phases are excluded by structural measurements. Therefore the origin of magnetisim of Co-ZnO as-deposited samples is suggested to be intrinsic.
3.The spin-dependent electrical transport and magnetoresistance in ZnO-based magnetic semiconductors have been studied experimentally andtheoretically. In Co-ZnO magnetic semiconductors a linear relation of lnρversusT~(1/2), which shows different slopes and intersections at different magnetic fields, is observed experimentally in the low temperature range. In Fe-ZnO magnetic semiconductors, a universal form of the resistance versus temperature, i.e.,lnρ~∞T_H /T + (T_(ES)/T)~(-1 2), is observed experimentally at different magnetic fields. The spin-dependent variable hopping model has been proposed by taking into account the electron-electron Coulomb interaction, the spin-spin exchange interaction and hard gap energy in the same frame, which can well described the observed magnetic transport properties in both Co-ZnO and Fe-ZnO magnetic semiconductor systems. Moreover, large negative magnetoresistance is observed at room temperature in ZnO-based magnetic semiconductors and the negative magnetoresistances are about 11% and 8% at 293K and 34% and 27% at 5K in Co-ZnO and Fe-ZnO magnetic semiconductors, respectively.
4.The ferromagnetism of ZnO-based magnetic semiconductors is explained by the modified scenario of the F-center mediated ferromagnetism. The oxygen vacancies are easily fromed in ZnO material. The oxygen vacanciy acts as a shallow doner in Co doped ZnO and traps an electron. Cansidering the interaction of the magnetic cations with the trapped hydrogenic electron in the impurity band, the trapped electrons tend to form bound magnetic polarons, coupling the 3d moments of the ions within their orbits. The interaction between the bound magnetic polarons by means of the shared impurity cations may be ferromagnetic at large concentrations of magnetic impurities. The strong interaction between the weakly localized s,p electrons of the oxygen vacancies and the strong localized d electrons of the Co may enhance the Curie temperature and saturation magnetization.
5.The polar Kerr rotation and ellipticity spectra of the as-deposited and annealed Co-ZnO magnetic semiconductors were studied. The Kerr rotation spectra versus the photon energy can be greatly modulated by adjusting the Co concentrationor annealing the samples. Moreover, the observed maximal Kerr rotation, 0.72°in anannealed sample is higher than those of pure Co films, Pt/Co multilayers and Pt_xCo_(1-x) alloys. The enhanced Kerr rotation in the annealed samples can be explained by the fact that the annealed samples became a nanocomposite system consisting of Co clusters and Co-ZnO magnetic semiconductor.
6. Ferromagnetic resonance is used to study Fe-ZnO magnetic semiconductors. The angular dependence of ferromagnetic resonance field for the samples with different compositions was studied. As the Fe content increases, the saturation magnetization increases, and the resonance field in normal resonance mode increases. The linewidth of the ferromagnetic resonance reduces as the Fe content increases, indicating that the inhomogeneity in chemical composition reduces with increasing Fe content. Therefore, suitably increasing Fe content is favorable to obtain magnetic semiconductor films with high saturation magnetization at room temperature.
引文
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