反铁磁耦合软磁/硬磁双层膜体系的交换弹性反磁化特性

基于微磁学理论研究了软磁/硬磁反铁磁交换耦合双层结构体系的反磁化特性,利用一维原子链模型模拟了其反磁化过程。研究表明:当考虑了软磁层的磁晶各向异性能后,随着软磁层厚度的增大,交换弹性反磁化过程从可逆过程转变为不可逆过程。存在一个临界的软磁层厚度tc,当软磁层厚度tstc时,交换弹性反磁化过程为不可逆过程。形核场Hb随软磁层厚度的变化仅当体系的反磁化过程为可逆的交换弹性反磁化过程时才满足经验公式Hb=Hb0/tsn。     

界面掺杂FeMn对CoFe/CrPt交换偏置体系的影响

采用磁控溅射的方法制备了CoFe/CrPt钉扎的交换偏置体系,用外加磁场真空退火以获得钉扎场.通过把反铁磁的FeMn掺入到该钉扎体系中发现,约0.7nm厚度的FeMn掺入在CoFe/CrPt的界面时,可以使体系的钉扎场从原来的5.6×103A/m增加到1.55×104A/m,而体系的Blocking温度仍然可以达到600℃.     

NiO/CoFe双层膜的交换机制研究

通过改变制备NiO薄膜的氩气压和衬底材料,研究了NiO的结构、表面粗糙度对NiO/CoFe双层膜交换耦合场Hex的影响.实验表明完全自旋未补偿面与交换耦合场的产生没有直接联系,但交换耦合场Hex与界面状况密切相关.增大NiO的表面粗糙度会使交换耦合场Hex减小.应用随机场理论在考虑了实际界面存在的粗造度、杂质和缺陷等实际情况下,正确地预测了交换耦合场的数量级,而且对交换耦合场与铁磁层厚度tFM、反铁磁层厚度tAFM以及交换耦合场的温度特性等实验结果做出了合理解释.并应用随机场模型对反铁磁/铁磁双层膜中铁磁层矫顽力Hc与铁磁层厚度tFM的关系进行了定量计算,发现矫顽力Hc与铁磁层厚度1/tFM成正比,这一结果表明理论计算与我们的实验数据符合得很好.     

织构和界面粗糙度对NiFe/FeMn双层膜交换偏置场的影响

采用磁控溅射方法制备NiFe/FeMn双层膜（分别以Ta、Cu作为缓冲层,Ta作为保护层）。实验发现,以Ta为缓冲层的NiFe/FeMn双层膜的交换偏置场比以Cu为缓冲层的NiFe/FeMn双层膜的交换偏置场大,而矫顽力却很小。我们从织构、界面粗糙度两方面对其中的原因进行了分析。以Ta为缓冲层的NiFe/FeMn双层膜有好的织构且NiFe/FeMn界面较平滑,这引起了较强的交换偏置场和较低的矫顽力。     

氧化物反铁磁Cr2O3薄膜的研究进展

氧化物反铁磁Cr2O3薄膜在自旋电子学器件中有着广泛的应用.重点论述了反铁磁Cr2O3的早期基础性研究,以及反铁磁Cr2O3薄膜在交换偏置和磁电效应方面的研究进展.最后指出了氧化物反铁磁Cr2O3薄膜研究中存在的部分问题,并展望了它的发展前景.     

硬磁/反铁磁交换耦合对反铁磁FeMn稳定性影响研究

采用磁控溅射方法在SiO2基体上制备了FePt/FeMn/NiFe/Ta多层膜样品,通过FeMn/NiFe双层膜交换偏置的变化研究了硬磁FePt不同磁化状态对反铁磁层FeMn的影响。实验表明,磁化了的L10相FePt能使FeMn在较薄的情况下（4.5nm）对NiFe产生比较强的交换偏置;而未被磁化的FePt对FeMn/NiFe交换偏置影响并不明显。认为更薄的反铁磁层对另外的铁磁层产生交换偏置是由于硬磁与反铁磁的界面交换耦合作用能增强反铁磁的稳定性。     

交换耦合软/硬磁双层膜体系磁动力学性质的研究

基于Laudau-Lifshitzt方程,在一维原子链模型的框架内研究了交换耦合软/硬磁双层膜体系的磁动力学性质,得到了软磁层在磁反转前处于一致磁结构和交换弹性磁反转过程中处于螺旋磁结构时的本征自旋波模式的频率及其空间分布特点,以及自旋波色散关系曲线。研究表明,软磁层的反磁化机制与自旋波的软模现象有密切关系,一阶自旋波模式的软化诱导了软磁层的磁反转,且磁反转的形式与一阶自旋波模式的空间分布状态相关。由磁动力学方法得到的磁反转临界场与近似的解析解得到的结果一致。     

Mn成分对CoFe/Pt_(50)(Cr_(100-x)Mn_x)_(50)体系交换偏置的影响

采用直流磁控溅射的方法制备了CoFe/Pt-CrMn交换偏置体系,反铁磁的Pt-CrMn是利用[Pt/CrMn]n多层膜并经过300℃、2h的退火获得。通过调整Mn的成分,系统地研究了体系交换偏置场的变化。获得了钉扎性能良好的L10相反铁磁钉扎材料Pt-CrMn,即CoFe/Pt50(Cr88Mn12)50钉扎体系,其界面交换耦合能为0.22×10-7J/cm2,截止温度(blocking temperature)为480℃。     

NiO/FeCo磁性多层膜的高频磁性

制备了一系列具有铁磁/反铁磁交换偏置作用的[NiO/Fe65Co35]10多层膜,使用振动样品磁强计(VSM)测量了样品的静磁参数,利用微带线法测量了样品4GHz-10GHz的磁谱,首次制备并测得了自然共振频率(fr)在6GHz以上,最高到fr=9.6GHz的薄膜样品。结果表明交换偏置场(Hex)、各向异性场(Hua)、以及矫顽力(Hc)随铁磁层厚度(tFM)增大而减小;基于Landau-Lifishitz(L-L)方程对静磁参量和磁谱进行了比较,发现样品自然共振频率较L-L方程计算值偏大30%以上。     

磁性材料交换偏置效应研究进展

磁性材料中交换偏置效应对自旋电子学的基础研究和应用发展起到了至关重要的作用,因此也成为无机非金属材料的研究中最为活跃的领域之一.由于交换偏置效应来源于铁磁/反铁磁界面处的交换耦合作用,所以相关的研究工作主要集中在铁磁/反铁磁双层膜体系;在一些基态为反铁磁的类钙钛矿锰氧化物中,由于存在相分离形成的铁磁团簇也观察到了交换偏置现象;此外,很多磁性材料纳米化后也出现了交换偏置效应.主要从这3方面介绍了在新材料体系中交换偏置效应的研究进展,以及交换偏置效应在自旋相关器件中的应用,提出了一些研究中面临的挑战并对发展方向作出展望.     

Auger electron spectroscopy analysis of interface roughness of Fe/Cr bilayers

In this work we investigate the surface and interfacial properties of Fe/Cr and Cr/Fe bilayers before and after annealing using Auger electron spectroscopy (AES). The roughness of the interface is also determined with the X-ray reflection method. The fitted values of inelastic mean free path λ_{Cr in Fe} reproduce the calculated value for Cr in Fe well, whereas the values of λ_{Fe in Cr} are significantly larger than the calculated ones, suggesting mutual segregation of atoms during growth. The low-energy range Auger spectra demonstrated that the MNN lines of Cr covered with Fe and Fe covered with Cr disappear after the deposition of 1 nm overlayer, this being an indication of continuous deposited film, but not excluding mixing at interfaces. The results of X-ray reflectometry measurements, which give the values of Fe/Cr and Cr/Fe roughness, are in accordance with this observation. The LMM Auger spectra of annealed samples showed that at the largest applied temperature, Cr diffuses into Fe, but the reverse effect of Fe diffusion into Cr is not observed.     

NiFe/IrMn多层膜制备及MgO掺杂研究

采用磁控溅射制备了Ta/NiFe/IrMn/Ta薄膜,研究了反铁磁IrMn的溅射功率和铁磁层NiFe厚度对多层膜交换偏置场的影响。在反铁磁IrMn中插入MgO,发现MgO含量对交换偏置场有一定影响。随着MgO含量的增加,多层膜的交换偏置场逐渐增大,当MgO的含量约为2.5%交换偏置场达到最大值。随着MgO含量进一步增加交换偏置场下降。在IrMn中插入适量的MgO可以有效地增加交换偏置场。     

Competition between ferromagnetic and antiferromagnetic interaction in monoclinic LiMnO2

The electronic and magnetic structures of monoclinic LiMnO₂ are investigated by first-principles calculations with spin-polarized generalized gradient approximation. It is found that the Mn³⁺ ion is in the high-spin state. The ground state is found to be an insulating state with competing ferromagnetic and antiferromagnetic interaction, and it is this competition that results in the spin-glass behavior observed in monoclinic LiMnO₂.     

基于NiMn的铁磁/反铁磁系统中交换偏置研究进展

NiMn合金薄膜作为一种高性能的反铁磁材料在巨磁电阻器件中具有重要的应用前景,引起了物理学及材料学等领域广大科研工作者的浓厚兴趣。综述了NiMn合金薄膜的基本性质,并对NiMn基铁磁/反铁磁双层膜的交换偏置的基本特征进行了分析。     

Microstructure and optical properties of cubic AlN/TiN bilayers deposited by laser molecular beam epitaxy

AlN/TiN bilayers were deposited on Si(100) substrates with varying laser pulse energy by laser molecular beam epitaxy (LMBE) technique, and their growth mode, crystal structure and optical properties were investigated. The results indicated that atomically flat TiN single films and AlN/TiN bilayers with layer-by-layer growth mode were successfully grown on Si(100) substrates at optimal laser pulse energy. Both TiN and AlN in the grown bilayers exhibited the NaCl-type cubic structure with the same (200) preferred orientation, showing an excellent epitaxial relationship. TiN single film was more reflective in the infrared range and presented a small transparent window centered at wavelength of 404 nm. Reflectance spectrum of AlN film on top of TiN indicated the sharp absorption at about 246 nm, yielding a bandgap energy of 5.04 eV comparable to the theoretical calculation of bulk cubic AlN, but scarcely reported by the experimental data.     

Tuning exchange spring effects in FePt/Fe(Co) magnetic bilayers

Structural and magnetic properties of exchange spring magnets consisting of hard magnetic (FePt) and soft magnetic (Fe and Co) bilayers, prepared by ion beam sputtering method are studied via X-ray diffraction (XRD), magneto-optic Kerr effect (MOKE) and vibrating sample magnetometry (VSM). Thin tracer layers of ⁵⁷Fe were introduced in the soft layer in order to observe the Fe spin structure and interfacial diffusion by Conversion Electron Mössbauer Spectroscopy (CEMS). The observed in-plane exchange spring behavior extends also to the magnetic hard layer, whose switching field can be tuned in an unexpected manner via the top soft magnetic layer. To explain the observed phenomenon it is suggested that the increased switching field, found in the system with a Co/Fe bilayer acting as a single soft magnetic layer, is compatible with a peculiar behavior of the stiffness coefficient of the heterogeneous soft magnetic layer. According to this observation, possibilities to maximize the exchange spring effects via suitably chosen non-homogeneous soft magnetic layers are open.     

Study of TiN/BN bilayers produced by pulsed arc plasma

Bilayers of TiN/BN were produced by using a PAPVD (Plasma Assisted Physical Vapor Deposition) pulsed vacuum arc system. The equipment is formed by a reactor composed by a vacuum chamber with two face-to-face electrodes and an RLC circuit to produce the arc discharge. To obtain the BN coating a target of h-BN was used placed on the cathode and a substrates of silicon placed on the anode. The work gas was nitrogen at a pressure of 4.4×10⁻¹ mbar and a voltage of 240 V. In order to improve the adherence of the BN film, an interlayer of TiN was grown. In this case the chamber was filled with N₂ to produce the TiN coating, with a pressure of 1.7 mbar and a voltage of 300 V. By means of XRD (X-ray diffraction), the existence of TiN was determined finding different crystalline orientation in FCC phase. An FTIR (Fourier Transform Infrared Spectroscopy) was employed to determine sp³/sp² bonding ratio in the BN film.By plotting I-V curves the electrical properties of the bilayer were studied, observing a semiconductor behavior and this result was compared to the silicon substrate without coating.     

Underlayer dependence of microtexture, microstructure and magnetic properties of c-axis oriented strontium ferrite thin films

Strontium ferrite (SrM) thin films were prepared by dc magnetron sputtering system on thermally oxidized silicon wafer (SiO₂/Si), single-crystal sapphire with (00l) orientation and single-crystal MgO with (111) orientation and the effect of Au and Pt underlayers on morphology and magnetic properties was studied. Experimental results revealed that with the application of underlayers, the crystallization temperature of SrM was reduced. Strontium ferrite thin films with uniaxial anisotropy were formed on all substrate specimens. Comparison of the results obtained on all thin films indicated that the maximum saturation magnetization and coercivity in the perpendicular direction were 0.377 T and 0.382 MAm^− 1, respectively, for thin films with Au underlayer and SiO₂/Si substrate.     

Cooling rate induced variation in microstructure and magnetic structure of Nd60Fe30Al10 glass forming alloy

Cooling rate induced variation in microstructure and magnetic structure was investigated in the as-cast Nd₆₀Fe₃₀Al₁₀ alloy. Because the cooling rate was different from the periphery to the center regions, apparent evolution from a full amorphous to a partial precipitated crystalline structure was observed in one as-cast sample. Corresponding to different microstructures, two magnetic domain structures, i.e. fine strip-like domains in sub-micron scale and sunflower-like domains in micron scale, were observed at the periphery and the center of a cross section, respectively. The variation of magnetic properties was discussed in the view of exchange interaction coupling.     

Effects of PyC shell thickness on the microstructure,ablation resistance of SiCnws/PyC-C/C-ZrC-SiC composites

SiC nanowires/pyrocarbon (SiCnws/PyC) core-shell structure toughened C/C-ZrC-SiC composites were fabricated by CLVD process,and the influences of PyC shell thickness on the microstructure and ablation resistance of the composites were researched.The results presented that SiCnws/PyC core-shell structure had a linear shape,and the composites became dense with the increasing PyC thickness.When the thickness of PyC shell increased from 0 to 2.4 μm,the density and thermal conductivity of the composites was improved gradually,but the coefficient of thermal expansion (CTE) decreased firstly and then increased.After the ablation test for 90 s,the ablation rates of the composites decreased continuously as the PyC thickness increased from 0 to 1.4 μm,but increased when the PyC thickness was up to 2.4 μm.Especially when the PyC thickness was 1.4 μm,the linear and mass ablation rates of the composites were 71.25 ％ and 63.01 ％ lower than those of the composites without PyC shell.The reasons behind the remarkable improvement of anti-ablation property were that the proper PyC thickness could alleviate the CTE mismatch to promote the formation of complete oxide coating,improve the thermal conductivity to reduce heat corrosion and enhance the capability to limit the mechanical erosion.