A study on CoFe/p-Si interfacial structures before and after swift heavy ion irradiation

Interfacial structures of CoFe/p-Si have been studied before and after the swift heavy ion (～100?MeV, Ni⁷⁺) irradiation to investigate its electronic and magnetic behavior. X-ray diffraction (XRD), atomic force microscopy, magnetic force microscopy and magnetization characteristics (M–H) from vibrating sample magnetometer (VSM) techniques have been used for the above. XRD data have confirmed the formation of the CoFe alloy phase along with the silicide phases of Fe and Co. It is observed that there is an irradiation-induced growth in crystallite but surface remains smooth with a surface roughness of ～34?nm. A very significant increase has been observed in the magnetization and that too with irradiation dose as compared with unirradiated ones, maintaining their superparamagnetic behavior. The results could be understood due to the role played by various magnetic phases in the structure. The magnetic field sensitivity on electronic transport across the structures has also increased in a significant manner after the irradiation as compared with unirradiated ones. The magnetic field sensitivity has resulted in an MR of 20%. The results could be understood due to the irradiation induced interfacial intermixing to result in increased magnetic phases of silicide for the observed significant magnetic behavior on the irradiation.     

Electronic and magneto-transport study across swift heavy ion irradiated exchange coupled Fe/NiO bilayer on Si substrate

Low temperature electronic and magneto-transport study across Fe/NiO bilayer on Si substrate has been reported. These bilayer structures have been irradiated by swift heavy ions (~100 MeV Fe⁷⁺ ions with a fluence of 5×10¹² ions/cm²). The electronic transport study across such bilayer (both unirradiated and irradiated) structures has shown the semiconducting nature of the interface. A significant decrease in current has been observed for the irradiated structure (as compared to unirradiated ones on the irradiation) which could be due to the irradiation induced introduction of defects/disorders in the structure. The magneto-transport study across unirradiated structure has shown the magnetic field sensitivity at low temperatures only whereas the irradiated structure has not shown any perceptible magnetic field sensitivity at low temperatures. Such observed intriguing feature of magnetic field sensitivity across the bilayer structures could be understood due to the motion of thermally assisted magnetic domain walls in the presence of external applied magnetic field. The observed high % MR could be related to spin-dependent electron scattering at the interfaces.     

The influence of ultraweak ionizing irradiation on the magnetoplastic effect in single crystals of a C<Subscript>60</Subscript> fullerite

The suppression of plasticity sensitivity of a C₆₀ fullerite to the action of a magnetic field is revealed. It is found that the C₆₀ fullerite undergoes temporary softening due to irradiation with ultralow (<0.1 cGy) doses of β and γ radiation.     

Irradiation-induced magnetism in graphite: a density functional study

Recent experiments indicate that proton irradiation triggers ferromagnetism in originally nonmagnetic graphite samples while He ion bombardment has a much smaller effect. To understand the origin of irradiation-induced magnetism, we have performed spin-polarized density functional theory calculations of the magnetic properties of the defects which are most likely to appear under irradiation vacancies and vacancy-hydrogen complexes. Both defects are magnetic, but as for the latter we find that H adsorption on one of the vacancy dangling bonds gives rise to a magnetic moment double that of the naked vacancy. We show that for small irradiation doses vacancy-hydrogen complexes result in a macroscopic magnetic signal which agrees well with the experimental values.     

Fabrication,Investigation, and Application of Doped Indium Antimonide Microcrystals in Radiation-Resistant Sensors

Results of investigations into the physical properties and radiation stability of InSb microcrystals grown from the vapor phase are presented. The effect of Sn, Al, and Cr dopants on the parameters of microcrystals and their stability to high-energy neutron irradiation are examined. It is reported that microcrystals have already been used in magnetic field sensors and magnetic measuring systems operating under irradiation.     

Effect of γ-ray irradiation on the magnetic properties of NdFeB and Fe–Cr–Co permanent magnets

The effect of γ-ray irradiation on the magnetic properties of NdFeB and Fe–Cr–Co permanent magnets has been investigated. The magnetic flux loss of two kinds of magnets before and after irradiation was measured. Results show that the effect of γ-ray irradiation on the magnetic properties of sintered NdFeB is not so obvious as that on Fe–Cr–Co magnet. Irradiation-induced damage from γ-ray for the Fe–Cr–Co magnets was characterized for the first time. The decline of permanent magnetic properties of Fe–Cr–Co magnet induced by γ-ray irradiation is reversible except for the maximum energy product (BH)_max. The difference of coercivity mechanism between these two kinds of permanent magnets is responsible for the different dependence of magnetic properties loss induced by γ-ray irradiation.     

重离子治癌的磁扫描照射野形成法

在论述重离子治癌照射的基本思想及其特点的基础上,着重对磁扫描照射野形成的两种技术路线——点扫描和栅扫描的优缺点进行了分析阐述.初步给出了 HIRFL上的重离子治癌终端磁扫描相关参数. The basic principle and characteristic of irradiation in heavy ion radiotherapy are introduced. Based on the basic principle and characteristic of irradiation in heavy ion radiotherapy, two magnetic scan methods for creating uniform irradiation field--the spot scan and the raster scan, are compared briefly. The parameter requests to the magnetic scanning system of the heavy ion radiotherapy facility planned in IMP(Institute of Modern Physics) are presented.     

Field-cycled PEDRI imaging of free radicals with detection at 450 mT

This paper describes the design, construction and use of a field-cycled proton-electron double-resonance imaging (FC-PEDRI) system for the detection and imaging of free radicals. The unique feature of this imager is its use of a 450-mT detection magnetic field in order to achieve good image quality and sensitivity. The detection magnetic field is provided by a superconducting magnet, giving high stability and homogeneity. Field cycling is implemented by switching on and off the current in an internal, coaxial, resistive secondary magnet that partially cancels the superconducting magnet's field at the sample; the secondary magnet is actively shielded to avoid eddy currents. EPR irradiation takes place at approximately 5 mT, following which the field is switched to 450 mT in 40 ms for NMR signal detection. Full details of the imager's subsystems are given, and experiments to image the distribution of stable free radical contrast agents in phantoms and in anesthetized rats are described.     

AFM and electronic transport studies of swift heavy ion irradiated Mn/p-Si bilayer structure

Mn/p-Si structures have been realised by electron beam evaporation of manganese on etched and cleaned p-Si wafers. Bilayer structures have been irradiated by swift heavy ions (of 100 MeV Fe⁷⁺ having a fluence of 1 × 10¹³ ions/cm²). The electronic transport features across the bilayer of the structure (i.e. I–V characteristics across the Mn/p-Si interface) show a significant increase of current (by two orders of magnitude) for the irradiated ones as compared to un-irradiated ones. I–V characteristics across the interface has also been recorded in presence of in-plane (i.e., along the plane of the interface) magnetic field which show a significant magnetic field sensitivity for the irradiated ones. The surface morphological studies from AFM show a granular structure with open face having micro-particles in it, prior to the irradiation and round shaped embedded granular structure after the irradiation. XRD data show the formation of manganese silicide (Mn₅Si₂). The results are understood in the realm of interfacial intermixing which is tailored by the swift heavy ion irradiation.     

Observations on the thermoluminescence signal induced by alpha radiation

Experimental observations of changes in thermoluminescence sensitivity of a polymineral fine-grain sample are reported. A repeat alpha regeneration experiment, involving multiple cycles of heating and alpha irradiation revealed a sensitivity decrease. It was further investigated whether this effect is caused by irradiation or heating. Our experiments show that repeated thermal treatments result in an increase in thermoluminescence (TL) sensitivity. This is in contrast to the effect of cycles of alpha irradiation which led to a decrease in TL sensitivity. This decrease was found to be dependent on the alpha irradiation history.     

The effect of damage on the superconducting and magnetic transition in ErRh4B4

Thin films of ErRh₄B₄, which exhibit both the superconducting and magnetic transitions observed in the bulk, were damaged by irradiation with 1.8 MeV α-particles. The dependence of T_c of the film on fluence, and the resulting resistance ratio, is very similar to that of A15 materials. The ferromagnetic transition is also rapidly depressed by damage. The results raise interesting questions concerning the band structure of cluster compound superconductors, the nature of the magnetic transition in ErRh₄B₄ and the generality of the sensitivity of cluster compounds to damage.     

Investigation of stability of ITER candidate Hall sensors under neutron irradiation

Hall sensors offer an attractive true non-inductive method of magnetic field measurements for fusion reactors. Their use for steady state magnetic diagnostics of ITER is presently limited by their questionable radiation and thermal stability. Issues of stable and reliable operation in ITER like radiation and thermal environment are addressed by the contribution. Recently, novel Hall sensors, compatible with temperatures up to 200°C, were developed and their radiation stability was tested at LVR-15 experimental fission reactor. Overview of the experimental set-up on LVR-15 reactor is given. Degradation of the sensor’s sensitivity by several tens of percents was observed after neutron irradiation by the total neutron fluence of 2 × 10¹⁷ n/cm² in LVR-15. This level of neutron fluence is comparable to that expected to occur over the whole ITER life time for a sensor location just outside the ITER vessel. The in-situ recalibration techniques are expected to handle the observed degree of Hall sensors performance degradation in ITER environment.     

Formation of the nanodots and change of the characteristics of thin magnetic films under laser irradiation

Results of experimental investigations of laser radiation interaction with the Ti, Co, NiFe, TbFe and LaSrMnO₃ films are presented. It is shown, that it is possible to improve magnetic characteristics and to obtain magnetic films with regular distribution of nanodots by the laser radiation. It is observed an increasing of magnetic permeability and the reduction of the coercive force after irradiation of the NiFe films by the nanosecond laser pulses that are induced by the substantial growth of the size of the nanodots in the process of recrystallization. Magnetic nanodots of 100–200 nm size are produced by the method of the laser cutting of the continuous magnetic films, or are formed in a nonmagnetic matrix by the diffusion in the multilayered films and oxidization of TbFe and LaSrMnO_3−x films at the irradiation of the nanosecond laser pulses.     

质子辐照对永磁合金微观结构演化的研究

钐钴和钕铁硼稀土永磁合金已经广泛应用于粒子加速器的波荡器和其他器件中,作为加速器的重要组成部分,永磁合金在辐照环境中长期服役会出现磁性能损失的现象,这会影响束流的品质.为了探讨产生这个现象的微观机理,采用透射电镜对质子辐照前后的钐钴和钕铁硼稀土永磁合金进行了微观结构演化的表征和分析,统计了由辐照析出的纳米晶体积密度和粒径分布,并讨论了微观结构演化对宏观磁性能损失的影响.结果表明,随着质子辐照损伤程度的增加,永磁合金的微观结构从单晶结构转变为纳米晶多晶结构,且纳米晶和基体的晶体结构相同.钕铁硼的纳米晶体积密度先增大后减小,粒径分布先增大后不变;钐钴的纳米晶体积密度逐渐减小,粒径逐渐增大.在2 dpa的质子辐照损伤程度下,钕铁硼稀土永磁合金比钐钴永磁合金的非晶化趋势更明显.     

Comparison of electron beam and pulsed laser irradiation effects in Fe80B20

The effects of high-energy electron beam and pulsed excimer laser irradiation on the magnetic properties of Fe₈₀B₂₀ amorphous alloy are investigated by means of transmission and conversion electron Mössbauer spectroscopy (CEMS) and scanning electron microscopy (SEM). Both types of irradiation were found to induce changes in the magnetic anisotropy of Fe₈₀B₂₀, but the influence of high-energy electron beam irradiation was weaker. Depending on the number of applied laser pulses and repetition rate, controlled magnetic anisotropy and/or relaxation of internal stresses could be obtained by excimer laser irradiation. The presence of molten zones subsequently solidified and of laser-induced internal stresses supports the model of closúre domain structure.     

Interface study of ion irradiated Cu/Ni/Cu(0 0 2)/Si magnetic thin film by X-ray reflectivity

The irradiation effect of 1 MeV C⁺ on the interface and magnetic anisotropy of epitaxial Cu/Ni system with a perpendicular magnetic anisotropy was investigated by using magneto-optical Kerr effects, grazing incident diffraction and X-ray reflectivity. The magnetic easy-axis was altered from the direction along the surface normal to in-plane and the strain in the Ni layer was relaxed after ion irradiation. Though the interface between the top Cu layer and the Ni layer becomes rough, the contrast of electron densities of Cu and Ni layer increases and the grain-growth occurs during ion irradiation. These phenomena arise from thermo-chemical driving force, i.e. heat of formation, which may be a crucial factor in determining the interface shape in the case of indirect energy transfer mechanism. Therefore, the change of the magnetic anisotropy of the Ni/Cu system after ion irradiation is not due to the formation of the intermixed layer at the interface. The ion irradiation effects on the grain-growth and enhancement of the electronic contrast between Ni and Cu are explained by the interfacial atomic movement caused by thermo-chemical driving force.     

X-ray absorption analysis of sputter-grown Co/Pt stackings before and after helium irradiation

We have studied the local order around cobalt atoms in Pt/Co/Pt layered systems gradually modified by irradiation using 30 keV helium ions. Using X-ray diffraction and X-ray Absorption Fine Structure, we have determined the crystallographic order, the number of Co-Co and Co-Pt bonds and the corresponding bond lengths both in-plane and in the perpendicular direction. The comparison with an interdiffusion model highlights the unexpected complexity of the initial Pt/Co/Pt nanostructure. We use the Néel/Bruno model of magnetic anisotropy to correlate the structure and the magnetic hysteresis properties. We then identify the structural consequences of irradiation onto the short range order. The irradiation induces a substitutional mixing maintaining the initial crystallographic structure. We confirm that the mixing rate is in agreement with a ballistic mechanism of mixing. In addition, we show that the previously reported irradiation-induced controlled decrease of the magnetic anisotropy can not be solely attributed to Co-Pt intermixing: irradiation also significantly releases the 3.4% tensile strain of the cobalt-rich dense planes. We finally speculate on the class of magnetic materials the concept of light ion irradiation could be extended to.     

Modification of magnetic anisotropy in metallic glasses using high-energy ion beam irradiation

Heavy ion irradiation in the electronic stopping power region induces macroscopic dimensional change in metallic glasses and introduces magnetic anisotropy in some magnetic materials. The present work is on the irradiation study of ferromagnetic metallic glasses, where both dimensional change and modification of magnetic anisotropy are expected. Magnetic anisotropy was measured using Mössbauer spectroscopy of virgin and irradiated Fe₄₀Ni₄₀B₂₀ and Fe₄₀Ni₃₈Mo₄B₁₈ metallic glass ribbons. 90 MeV ¹²⁷I beam was used for the irradiations. Irradiation doses were 5×10¹³ and 7.5×10¹³ ions/cm². The relative intensity ratios D ₂₃ of the second and third lines of the Mössbauer spectra were measured to determine the magnetic anisotropy. The virgin samples of both the materials display in-plane magnetic anisotropy, i.e., the spins are oriented parallel to the ribbon plane. Irradiation is found to cause reduction in magnetic anisotropy. Near-complete randomization of magnetic moments is observed at high irradiation doses. Correlation is found between the residual stresses introduced by ion irradiation and the change in magnetic anisotropy.     

激光陀螺本征模偏振态与磁敏感特性的理论研究

环境磁场的干扰是影响激光陀螺精度的重要因素之一. 为了减小二频机械抖动激光陀螺的磁敏感性, 推导了环形腔的琼斯矩阵, 其中考虑了非共面角、增益介质、腔损耗、腔镜反射各向异性和应力双折射, 采用矩阵本征问题求解的摄动理论分析了环形腔的偏振态和磁敏感特性. 研究表明, 为了减小激光陀螺的磁敏感性, 应减小非共面角和腔损耗, 增大腔镜的反射各向异性. 腔镜应力双折射究竟会增大还是减小磁敏感性与应力作用主轴、受应力腔镜的位置有关, 此外它还会引起顺时针和逆时针模式之间的偏振非互易性. 磁敏感性与腔失谐近似成线性关系, 导致激光陀螺工作于增益峰值时磁敏感性并非最小. 这些结果对减小二频机械抖动激光陀螺的磁敏感性具有较好的指导意义. 关键词： 激光陀螺 磁敏感性 椭圆度 琼斯矩阵     

Oscillations of the magnetoresistance of a two-dimensional electron gas under microwave irradiation: Influence of the irradiation frequency

We present measurements of the magnetoresistance of a two-dimensional electron gas (2DEG) under continuous microwave as a function of the irradiation frequency. In a previous work by Simovič et al. [Phys. Rev. B 71 (2005) 233303], the magnetoresistance under microwave was shown to be modulated by oscillations of large amplitude that are periodic with magnetic field, their period and phase depending strongly on the electron density. Here we show that the phase and the amplitude of the microwave-induced oscillations also depend on the frequency of irradiation and the sign of the magnetic field.