磁性应力测量条件对应力感度的影响

磁性应力测量具有测量速度高,探测深度大(可达数毫米),无辐射危险,携带方便等优点.可以对使用中的构件进行实时实地且安全的测量.但磁性应力测量法只能用于铁磁材料并且对铁磁材料结构等因素也敏感.因此,在磁性应力测量中影响测量精度的原因很多,其中一个最主要的参数就是应力感度.本文主要研究了两种材料的应力感度与材料测定条件的关系,以及测定环境对应力感度的影响,从而在磁性测量的过程中能排除不利条件,正确地确定磁性应力的感度,提高磁性应力测量技术的准确度.     

Measurement of magnetic losses in resonant metallised ferrites

Microwave magnetic losses, far enough from the ferromagnetic resonance, are generally measured by perturbation methods, i.e. by comparing resonance of a cavity with and without magnetic sample. Nevertheless such methods require very accurate apparatuses, for parameters of the resonant cavity are slightly altered by the presence of the sample because of the relative smallness of the latter. The fore-going difficulty can be overcome by using the sample as a resonant cavity. The TM010mode of a cylindrical metallised sample are very convenient to achieve accurate measurement of magnetic losses. This method is quite effectual for materials with low magnetic moments and for low frequencies (from 1 to 5 GHz). Large metallic cavities are avoided and the apparatus is very simple.     

磁性材料磁热效应的研究

设计组装了一种冰量热计法磁致热效应测量仪,它可用于测量交变场下铁磁样品磁致热的绝对量。从磁热测量的结果,得到了一些单一磁样品和磁－良导体复合样品的磁致热效应实验规律。     

An automated compact vibromagnetometer for investigating soft magnetic materials

An automated vibration magnetometer for measuring the magnetization and hysteresis curves of soft magnetic materials at room temperature is described. The vibromagnetometer has a magnetic moment sensitivity of 5∙10^–6 Gs∙cm³, a measurement error of less than 3% and a magnetizing field strength range of up to ±200 Oe, which can be extended to ±10000 Oe using more powerful magnetic systems. Hysteresis characteristics of amorphous ferromagnetic microwire and of a printed text sign are presented.     

X-ray diffraction measurements in high magnetic fields and at high temperatures

Abstract

A system was developed measuring x-ray powder diffraction in high magnetic fields up to 5 T and at temperatures from 283 to 473 K. The stability of the temperature is within 1 K over 6 h. In order to examine the ability of the system, the high-field x-ray diffraction measurements were carried out for Si and a Ni-based ferromagnetic shape-memory alloy. The results show that the x-ray powder diffraction measurements in high magnetic fields and at high temperatures are useful for materials research.     

AC loss characteristics of YBCO conductors carrying transport currents in external AC magnetic fields

In this work we present dependence of AC losses in a YBCO tape conductor carrying an AC transport current in an external AC magnetic field on the angle between the direction of the external field and the tape face of the conductor. The losses were measured by a calorimetric method whose validity was proven by simultaneous electric and calorimetric measurements of the losses in the same part of the conductor. The experiment was conducted at 77 K. The measured data show that the AC losses are dominated by the normal component of the external magnetic field to the tape surface. It is also shown that the AC losses sharply drop when the external magnetic field is parallel to the tape surface, which is due to extremely high aspect ratio of the YBCO conductor.     

Low-Temperature Specific Heat of Graphite and CeSb2: Validation of a Quasi-adiabatic Continuous Method

We present the application of a fast quasi-adiabatic continuous method to the measurement of specific heat at ⁴He temperatures, which can be used for the study of a wide range of materials. The technique can be performed in the same configuration used for the relaxation method, as the typical time constants between calorimetric cell and thermal sink at 4.2 K are chosen to be of the order of τ～30 s. The accuracy in the absolute values have been tested by comparing them to relaxation-method results obtained in the same samples (performed in situ using the same set-up), with a deviation between the absolute values <3 % in the whole temperature range. This new version of the continuous calorimetric method at low temperatures allows us to completely characterize and measure a sample within a few hours with a high density of data points, whereas when employing other methods we typically need a few days. An exhaustive study has been performed for reproducibility to be tested. In the present work, we have applied this method to two different substances: CeSb₂, which exhibits three magnetic transitions at 15.5 K, 11.7 K and 9.5 K, and graphite, both highly-oriented pyrolytic graphite (HOPG) and natural crystals. Our results on these graphites are discussed in comparison with previous published data on different kinds of graphite samples.     

X-ray diffraction measurements in high magnetic fields and at high temperatures

A system was developed measuring x-ray powder diffraction in high magnetic fields up to 5 T and at temperatures from 283 to 473 K. The stability of the temperature is within 1 K over 6 h. In order to examine the ability of the system, the high-field x-ray diffraction measurements were carried out for Si and a Ni-based ferromagnetic shape-memory alloy. The results show that the x-ray powder diffraction measurements in high magnetic fields and at high temperatures are useful for materials research.     

Methods for measuring the Q-factor (or resistance) of induction coils at audio frequencies

Conclusions The above methods, especially those with the T-type circuits, may prove useful in studying coils, in testing, etc., for instance, in certifying coils used for checking the corresponding parameters of bridges (or Q-meters). They can also be used for evaluating losses in ferrites, ferromagnetic materials and other substances.     

Method for estimation of magnetic viscosity of ferromagnetics

A method providing quantitative estimation of the degree of magnetic viscosity of ferromagnetic materials by measurement of the phase of the signal from the measuring coil at field excitation by a sinusoidal signal in longitudinally extended samples with constant cross section is described. It is demonstrated that, in estimation of magnetic viscosity, it is necessary to take into account the sample size and shape, as well as the frequency of measurement. Additional information obtained by determination of the decrement of the signal from the measuring coil can be used together with the magnetic viscosity for determination of steel grade. Corresponding plots are presented.     

Viscosity-based magnetodynamic model of soft magnetic materials

A time-stepping method based on the concept of magnetic viscosity developed to reproduce the excess loss in electrical steel is proposed. A numerical scheme for simultaneous solution of Maxwell equations and equations describing the magnetic viscosity has been developed. The method is suitable for describing arbitrary magnetization regimes such as waveforms associated with pulsewidth modulation (PWM) voltage excitation, and the model differential equations can be conveniently combined with equations of an external electric circuit. The accuracy of the proposed dynamic model is shown using three nonoriented electrical steel as examples. Fitting of the magnetic viscosity parameters for one sinusoidal flux regime enables dynamic hysteresis loops and losses to be predicted with high accuracy over a wide range of frequencies and amplitudes of sinusoidal or nonsinusoidal flux densities.     

A novel experimental technique to determine the heat transfer coefficient between the bed and particles in a downer

A novel method for directly measuring the temperature history of mobile hot ferromagnetic particles (steel particles), substituting for reacting particles, in a binary-solid (reacting particles and inert particles) downflow is introduced. The temperature history of the hot steel particles can be obtained by measuring the temperature of the particles at different axial positions using magnetic fields that can separate the steel particles from other bed materials immediately and easily. Employing the magnetic marking method, magnetic sensors were used to detect the change in magnetic flux density in a given magnetic field, and the residence time of the steel particles was also measured. The cross-sectional averaged particle-to-bed heat transfer coefficients were calculated from the experimental results using simple heat balance equations. The measured temperature data have a relatively wide error range; however, the average temperature curves derived from the average particle-to-bed heat transfer coefficients agreed with the temperature plots. Therefore, the experimental method of this study is applicable to the measurement of the particle temperature in a binary-solid downflow. The results showed that there is strong correlation between the particle-to-bed heat transfer coefficients and normalized collision frequency under the laminar gas flow conditions.     

Microwave ferrites, part 2: passive components and electrical tuning

Low-loss ferrimagnets are the basis for passive microwave components operating in a wide range of frequencies. The magnetic resonances of passive components can be tuned using static magnetic fields over a wide frequency range, where higher operation frequencies require higher magnetic bias unless hexaferrites with large crystalline anisotropy are used. However, electrical tuning of the operation frequency, which can be achieved if the magnetic property of the material is sensitive to the field through magnetoelectric (ME) coupling, is more attractive than magnetic tuning. In the so-called multiferroic materials such as TbMnO₃, TbMn₂O₅, BiFeO₃, Cr₂O₃, and BiMnO₃, which possess simultaneously both the ferroelectric and ferromagnetic properties, ME coupling is very small to be practical. The ME effect, however, can be significantly enhanced in the case of bilayer/multilayer structures with one constituent highly piezoelectric, such as Pb(Zr_1 ? x Ti _x )O₃ (PZT) and 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ (PMN-PT), and the other highly ferromagnetic, opening up the possibility for a whole host of tunable microwave passive components. In such structures, the strain induced by the electric field applied across the piezoelectric material is transferred mechanically to the magnetic material, which then experiences a change in its magnetic permeability through magnetostriction. Additionally, electrical tuning coupled with high dielectric permittivity and magnetic susceptibility could lead to miniature microwave components and/or make operation at very high frequencies possible without the need for increased size and weight common in conventional approaches. In Part 1 of this review, fundamentals of ferrite materials, interconnecting chemical, structural, and magnetic properties with the treatment of various types of ferrites used in microwave systems are discussed. Part 2 discusses the basis for coupling between electrical and magnetic properties for highly attractive electrical tuning of passive components by combining piezoelectric materials with ferrites and various device applications of ferrites.     

Tuning the permeability spectra with a half-free ferromagnetic underlayer in (NiFe/IrMn)n exchange-biased multilayers

The influence of a half-free ferromagnetic underlayer on the static and microwave magnetic properties in [NiFe/IrMn]_n exchange bias multilayer thin film system has been systematically investigated. By changing the thickness of the half-free ferromagnetic underlayer, the linewidth of the ferromagnetic resonance (FMR) in this system can be tuned from 0.9 to 2.4 GHz. Theoretical fitting of the FMR frequencies based on the Landau-Lifshitz-Gilbert equation is also carried out to quantitatively identify the effective anisotropy fields and Gilbert damping parameters. The results provide an effective and flexible way to tailor the microwave permeability spectra and broaden the frequency linewidth toward the low frequency range in [ferromagnetic/antiferromagnetic]_n exchange bias multilayer films system. This approach has potential application for tunable wideband high frequency noise filters.     

Development and comparative analysis of fluxgate magnetic sensor structures in PCB technology

In this paper, we present a family of fluxgate magnetic sensors on printed circuit boards (PCBs), suitable for an electronic compass. This fabrication process is simple and inexpensive and uses commercially available thin ferromagnetic materials. We developed and analyzed the prototype sensors with software tools based on the finite-element method. We developed both singleand double-axis planar fluxgate magnetic sensors as well as front-end circuitry based on second-harmonic detection. Two amorphous magnetic materials, Vitrovac 6025X (25 /spl mu/m thick) and Vitrovac 6025Z (20 /spl mu/m thick), were used as the ferromagnetic core. We found that the same structures can be made with Metglas ferromagnetic core. The double-axis fluxgate magnetic sensor has a sensitivity of about 1.25 mV//spl mu/T with a linearity error of 1.5% full scale, which is suitable for detecting Earth's magnetic field (/spl plusmn/60 /spl mu/T full-scale) in an electronic compass.     

动态转矩测量技术的研究

采用磁栅转矩传感器和一种新的微机辅助相位差检测方法，研制了一套新型动态转矩测量系统。与现有的转矩测量仪器相比，该系统的测量受传动系统转速波动的影响很小，具有更高的测量精度、灵敏度和抗干扰性能。     

Development and analysis of a PCB vector 2-D magnetic field sensor system for electronic compasses

A high-sensitivity vector two-dimensional (2-D) magnetic sensor system for low magnetic field measurements has been realized and tested. The system, made in PCB technology, consists of a double-axis Fluxgate magnetic sensor and the readout electronic circuitry, based on second-harmonic detection. The amorphous magnetic materials Vitrovac 6025X (25 /spl mu/m thick) and Vitrovac 6025Z (20 /spl mu/m thick) were used as the ferromagnetic core of the sensor. By applying a sinusoidal excitation current having a 450-mA peak at 10 kHz with Vitrovac 6025Z, the measured magnetic sensitivity was about 1.25 mV//spl mu/T. This value seems to be adequate for the Earth's magnetic field detection (/spl plusmn/60 /spl mu/T). The full-scale linearity error was about 1.5%. By using the thicker Vitrovac 6025X and a sinusoidal excitation current having a 600-mA peak at 10 kHz, a maximum sensitivity of approximately 1.68 mV//spl mu/T with a linearity error of about 1.55% full scale in the range of /spl plusmn/60 /spl mu/T were measured. Due to the use of commercially available ferromagnetic materials, the vector 2-D magnetic sensor system presented is characterized by a very simple fabrication process, thus allowing low-cost devices to be designed.     

System for coil simulation measurements of losses and instabilities in superconducting wires

A new system for measuring ac losses in superconductors under coil simulation conditions is described. It is aimed to investigate instabilities in local points of a coil. Currents up to 150 A and magnetic fields up to 0.4 T can be applied simultaneously and can be varied independently. The magnetic and electric fields on both sides of the sample are measured by means of pick-up coilds and potential leads, respectively. By this method the instantaneous values of the power introduced through each of both sample surfaces can be measured separately. The validity of the method and the performance of the system are demonstrated by measuring the losses of a copper-clad single-core Nb---Ti---Zr wire for several values of the ratio between the current and the magnetic field, which are inphase.     

System for coil simulation measurements of losses and instabilities in superconducting wires

A new system for measuring ac losses in superconductors under coil simulation conditions is described. It is aimed to investigate instabilities in local points of a coil. Currents up to 150 A and magnetic fields up to 0.4 T can be applied simultaneously and can be varied independently. The magnetic and electric fields on both sides of the sample are measured by means of pick-up coils and potential leads, respectively. By this method the instantaneous values of the power introduced through each of both sample surfaces can be measured separately. The validity of the method and the performance of the system are demonstrated by measuring the losses of a copper-clad single-core Nb-Ti-Zr wire for several values of the ratio between the current and the magnetic field, which are inphase.     

Selective sensitivity of ellipsometry to magnetic nanostructures

Magneto-optic (MO) ellipsometry of ferromagnetic materials is extremely sensitive to ultra-thin films, multilayers, and nanostructures. It gives a possibility to measure all components of the magnetization vector in the frame of the magneto-optic vector magnetometry and enables us to separate magnetic contributions from different depths and materials in nanostructures, which is reviewed in this article. The method is based on ellipsometric separation using the selective MO Kerr effect. The figure of merit used to quantify the ellipsometric selectivity to magnetic nanostructures is defined on the basis of linear matrix algebra. We show that the method can be also used to separate MO contributions from areas of the same ferromagnetic materials deposited on different buffer layers. The method is demonstrated using both: (i) modeling of the MO ellipsometry response and (ii) MO measurement of ultra-thin Co islands epitaxially grown on self-organized gold islands on Mo/Al₂O₃ buffer layer prepared using the molecular beam epitaxy at elevated temperatures. The system is studied using longitudinal (in-plane) and polar (perpendicular) MO Kerr effects.