A Peltier cell calorimeter for the direct measurement of the isothermal entropy change in magnetic materials

We developed a calorimetric technique to measure the isothermal magnetocaloric entropy change. The method consists in the use of Peltier cells as heat flow sensor and heat pump at the same time. In this paper, we describe the setup, the constitutive equations of the Peltier cell as sensor and actuator, and the calibration procedure. The Peltier heat is used to keep the sample isothermal when magnetic field is changed. The temperature difference between the sample and the thermal reservoir is kept by a digital control within 5 mK for a magnetic field rate of 20 mT s(-1). The heat flux sensitivity around 1 microW. With this method, it is possible to measure the magnetocaloric effect in magnetic materials by tracing the curves of the exchanged entropy Delta(e)s as a function of the magnetic field H. The method proves to be, in particular, suitable to reveal the role of the entropy production Delta(i)s, which is connected with hysteresis. Measurement examples are shown for Gd, BaFe(12)O(19) ferrite, and Gd-Si-Ge.     

Temperature dependence dynamical permeability characterization of magnetic thin film using near-field microwave microscopy

A temperature dependence characterization system of microwave permeability of magnetic thin film up to 5 GHz in the temperature range from room temperature up to 423 K is designed and fabricated as a prototype measurement fixture. It is based on the near field microwave microscopy technique (NFMM). The scaling coefficient of the fixture can be determined by (i) calibrating the NFMM with a standard sample whose permeability is known; (ii) by calibrating the NFMM with an established dynamic permeability measurement technique such as shorted microstrip transmission line perturbation method; (iii) adjusting the real part of the complex permeability at low frequency to fit the value of initial permeability. The algorithms for calculating the complex permeability of magnetic thin films are analyzed. A 100 nm thick FeTaN thin film deposited on Si substrate by sputtering method is characterized using the fixture. The room temperature permeability results of the FeTaN film agree well with results obtained from the established short-circuited microstrip perturbation method. Temperature dependence permeability results fit well with the Landau-Lifshitz-Gilbert equation. The temperature dependence of the static magnetic anisotropy H(K)(sta), the dynamic magnetic anisotropy H(K)(dyn), the rotational anisotropy H(rot), together with the effective damping coefficient α(eff), ferromagnetic resonance f(FMR), and frequency linewidth Δf of the thin film are investigated. These temperature dependent magnetic properties of the magnetic thin film are important to the high frequency applications of magnetic devices at high temperatures.     

Feasibility of nondestructive determination of the fatigue limit of steel 20H2M

The regularity of variations of the stray magnetic field of steel 20H2M specimens characterized by residual magnetization is studied in the ranges of elastic and plastic deformation. A correlation of the field value, i.e., variations of the magnetic parameters (H _τ, H _0τ, and H _n), with the fatigue limit was found to exist. This finding offers scope for the determination of the fatigue limit with the use of a prompt procedure for the nondestructive testing of magnetoelastic parameters.     

激励磁场对力磁耦合作用的强化机制研究

力磁耦合作用是金属磁记忆检测等电磁无损检测技术的基础。为了探明外加激励磁场在不同应力水平下对力磁耦合作用的影响机制,从磁导率与应力及环境磁场变化关系的角度,在理论上计算了外加激励磁场下力磁耦合作用下与力和磁单独作用下的表面磁场强度之差ΔH,并推导出该差值随着拉应力的增大而增大的结论。用预制缺陷的45钢试样进行对照试验,发现激励磁场对力磁耦合作用的影响ΔH是随着应力的增大而呈类似指数形式递增的。经设计的正交试验验证,激励磁场与应力对磁信号的交互耦合作用显著,且在受力过程中激励磁场对信号的作用水平最大,这与理论分析结果吻合。说明外加激励磁场对力磁耦合作用起到了一定的强化作用。     

Fe-Ga磁特性测试装置改进与动态磁致伸缩实验

利用Fe-Ga磁特性测试装置进行动态磁致伸缩测量时,受激励线圈产生的磁场的影响,测试样品的应变通常偏大,本文对此做了分析并进行验证。通过分析Fe-Ga动态磁致伸缩测量过程,对原测试装置进行了改进。将样品的一端固定在极头上并调节激励磁场使其在样品饱和磁场附近,以消除机械振动对动态磁致伸缩测试产生的影响。采用多参数磁学测试系统和改进前后的Fe-Ga特性测试系统进行Fe-Ga静态和动态磁致伸缩特性测试实验。结果表明:采用改进的Fe-Ga磁特性测试装置可在低饱和场下精确测量动态应变。实验还测试了Fe-Ga在2.7kA/m偏置磁场作用下的动态磁致伸缩特性,结果表明:(1)偏置磁场作用下应变与磁场同频;(2)应变对磁场的滞后随磁场频率的增加而增大;(3)λ~H曲线为椭圆形且椭圆环的面积随频率的增大而增大。上述结果表明,本文提出的改进装置可有效消除振动产生的额外应变。     

Technique for high axial shielding factor performance of large-scale, thin, open-ended, cylindrical Metglas magnetic shields

Metglas 2705M is a low-cost commercially available, high-permeability cobalt-based magnetic alloy, provided as a 5.08-cm wide and 20.3-μm thick ribbon foil. We present an optimized construction technique for single-shell, large-scale (human-size), thin, open-ended cylindrical Metglas magnetic shields. The measured dc axial and transverse magnetic shielding factors of our 0.61-m diameter and 1.83-m long shields in the Earth's magnetic field were 267 and 1500, for material thicknesses of only 122 μm (i.e., 6 foil layers). The axial shielding performance of our single-shell Metglas magnetic shields, obtained without the use of magnetic shaking techniques, is comparable to the performance of significantly thicker, multiple-shell, open-ended Metglas magnetic shields in comparable-magnitude, low-frequency applied external fields reported previously in the literature.     

Measurement of magnetic susceptibility in pulsed magnetic fields using a proximity detector oscillator

We present a novel susceptometer with a particularly small spatial footprint and no moving parts. The susceptometer is suitable for use in systems with limited space where magnetic measurements may not have been previously possible, such as in pressure cells and rotators, as well as in extremely high pulsed fields. The susceptometer is based on the proximity detector oscillator, which has a broad dynamic resonant frequency range and has so far been used predominantly for transport measurements. We show that for insulating samples, the resonance frequency behavior as a function of field consists of a magnetoresistive and an inductive component, originating, respectively, from the sensor coil and the sample. The response of the coil is modeled, and upon subtraction of the magnetoresistive component the dynamic magnetic susceptibility and magnetization can be extracted. We successfully measure the magnetization of the organic molecular magnets Cu(H(2)O)(5)(VOF(4))(H(2)O) and [Cu(HF(2))(pyz)(2)]BF(4) in pulsed magnetic fields and by comparing the results to that from a traditional extraction susceptometer confirm that the new system can be used to measure and observe magnetic susceptibilities and phase transitions.     

Differential membrane-based nanocalorimeter for high-resolution measurements of low-temperature specific heat

A differential, membrane-based nanocalorimeter for general specific heat studies of very small samples, ranging from 0.5 mg to sub-μg in mass, is described. The calorimeter operates over the temperature range from above room temperature down to 0.5 K. It consists of a pair of cells, each of which is a stack of heaters and thermometer in the center of a silicon nitride membrane, in total giving a background heat capacity less than 100 nJ/K at 300 K, decreasing to 10 pJ/K at 1 K. The device has several distinctive features: (i) The resistive thermometer, made of a Ge(1 - x)Au(x) alloy, displays a high dimensionless sensitivity ∣dlnR∕dlnT∣ ? 1 over the entire temperature range. (ii) The sample is placed in direct contact with the thermometer, which is allowed to self-heat. The thermometer can thus be operated at high dc current to increase the resolution. (iii) Data are acquired with a set of eight synchronized lock-in amplifiers measuring dc, 1st and 2nd harmonic signals of heaters and thermometer. This gives high resolution and allows continuous output adjustments without additional noise. (iv) Absolute accuracy is achieved via a variable-frequency-fixed-phase technique in which the measurement frequency is automatically adjusted during the measurements to account for the temperature variation of the sample heat capacity and the device thermal conductance. The performance of the calorimeter is illustrated by studying the heat capacity of a small Au sample and the specific heat of a 2.6?μg piece of superconducting Pb in various magnetic fields.     

Research and development of H- ion source and low energy beam transport for a kaon-neutrino factory

A baseline H(-) ion source and low energy beam transport (LEBT) system have been identified for Project X. The filament-discharge H(-) ion source has been fabricated by D-Pace, Inc. and is now in operation at LBNL. The source is capable of delivering over 10 mA of H(-) beam in cw operation with normalized 4 rms emittances less than 0.7 π mm mrad. A two-solenoid magnetic lens LEBT system has been design. The design has been validated with simulations of beam transport for 5 mA 30 keV H(-) beams using various simulation codes.     

Superconducting quantum interference device setup for magnetoelectric measurements

A commercial superconducting quantum interference device (SQUID) setup (MPMS 5S from Quantum Design), equipped with a magnetic ac susceptibility option, is modified for measurements of the linear magnetoelectric (ME) effect, i.e., of the magnetic moment induced by an applied external electric field in a ME sample. Test measurements on a Cr(2)O(3) (111) single crystal are in excellent agreement with previously reported data of its ME susceptibility. The main advantages of the proposed setup are the improved precision due to the high sensitivity of the SQUID magnetometer in combination with the lock-in technique and a relatively simple experimental realization.     

Mapping inelastic intensities in diffraction patterns of magnetic samples using the energy spectrum imaging technique

We present the quantitative measurement of inelastic intensity distributions in diffraction patterns with the aim of studying magnetic materials. The relevant theory based on the mixed dynamic form factor (MDFF) is outlined. Experimentally, the challenge is to obtain sufficient signal for core losses of 3d magnetic materials (in the 700-900eV energy-loss range). We compare two experimental settings in diffraction mode, i.e. the parallel diffraction and the large-angle convergent-beam electron diffraction configurations, and demonstrate the interest of using a spherical aberration corrector. We show how the energy spectrum imaging (ESI) technique can be used to map the inelastic signal in a data cube of scattering angle and energy loss. The magnetic chiral dichroic signal is measured for a magnetite sample and compared with theory.     

电喷雾电离-四极杆飞行时间质谱法研究三种β_2-受体激动剂的质谱裂解特征

采用电喷雾电离 -四极杆飞行时间质谱 ( ESI-Qq TOFMS)联用技术 ,对三种β2 -受体激动剂克仑特罗( Clenbuterol)、沙丁胺醇 ( Salbutamol)和盐酸 SPFF进行碰撞诱导解离 ( Collision induced dissociation,CID)研究。将三种药物标准品用甲醇溶解至 0 .1μg/m L直接进样 ,选择正离子方式进行检测。以质子化准分子离子 [M+H]+ 作为内标物 ,对碎片离子进行了准确质量测定 ,确认了这些碎片离子的元素组成 ,探讨了该类化合物的质谱裂解规律。研究发现 :它们的 ESI-MS2质谱分别生成脱去 H2 O分子、叔丁氨基等的碎片离子 ,其中叔丁氨基碎片离子 ( m/z74)为三种药物共有的碎片离子 ,这些特征可为 β2 -受体激动剂类药物的体内代谢转化和定量分析研究提供有力的依据。     

Quantitative elastic modulus measurement by magnetic force modulation microscopy

It is experimentally demonstrated that magnetic force modulation microscopy (MFMM) is a technique allowing quantitative elastic modulus measurements. A model of the cantilever–tip–sample interaction taking into account the lateral contact stiffness (i.e., the friction effects at the level of the tip–sample contact), the position of the magnetic force applied to the cantilever with respect to the tip position, as well as the inclination of the cantilever arm with respect to the sample surface is presented. The model shows that MFMM is much less sensitive to lateral force than the other modulation techniques and thus, in contrast to the latter, that the contrast of the stiffness images can be interpreted as a true elasticity contrast and not as a mixture of friction and elasticity. Thanks to the study of the normal contact stiffness versus normal load that allows the characterization of contact between tip and sample, it is possible to perform quantitative elastic modulus measurements with a dynamic modulation method.     

Effect of elastoplastic deformation on magnetic characteristics of a powder structural steel having different residual porosities

The effect of porosity on the evolution of magnetic characteristics of a powder structural steel during deformation up to failure is shown by an example of steel 50H2M. The selection of a magnetic field such that the coercive force in a minor magnetic hysteresis loop weakly depends on the porosity is shown to be possible. It is supposed that the applied stress at which the minimum coercive force of such a minor hysteresis is observed corresponds to internal stresses of the porous material.     

A Torsion Balance for Studying Anisotropic Magnetic Properties of Superconducting Materials

A low-temperature torsion balance for studying magnetic properties of superconductors is described. The device can operate in the modes of the rotation or vibration of an axisymmetric superconducting sample in an external magnetic field. The balance provides for the measurement of a torque of 10^–8 –1 N·m applied to the sample. The device is highly sensitive to frozen magnetic fluxes even of the order of magnitude of the geomagnetic field (H 0.5 Oe). To eliminate the effect of frozen magnetic fluxes, two-layer Permalloy shields providing for the cooling of the sample in the field H < 10^–3 Oe are used. The capabilities of the developed method for studying critical parameters and the anisotropic magnetic properties of superconductors are described.     

Superconducting silver brazing alloy (silver solder)

A superconducting transition has been observed in a type BAg-3 silver brazing alloy (silver solder) with T(c)=96.(6) mK and H(c)=4.7 Oe. The associated diamagnetism indicates that approximately 1/3 of the sample volume displays the Meissner effect. This property dictates caution in its use at very low temperatures, particularly near sensitive magnetic devices such as ac and SQUID magnetometers.     

天然产物的质谱研究 Ⅷ.寡糖甙与Na~ 加合离子的快原子轰击质谱和质量分离离子动能谱

研究了三种糖甙与Na~ 加合离子的快原子轰击质谱(FABMS)和质量分离离子动能谱(MIKES)。实验结果表明,当把这几种糖甙与氯化钠(NaCI)一起加到基质中时,在FAB谱中出现丰度相当高的[M Na]~ 加合离子,它的丰度比[M H]~ 要高得多。[M Na]~ 离子的MIKES为这些甙所连糖的序列分析提供了方便的方法。     

Low cost auxiliary system for broadband NMR on strongly magnetic systems

A low cost auxiliary system consisting of He cryostat, superconducting magnet, and sample holder assembly with field probe has been constructed. The system meets the requirements of NMR on strongly paramagnetic or ordered magnetic materials, which are accurate temperature settings over a wide range, high NMR frequencies, high and accurate magnetic fields of moderate homogeneity, and exact crystal orientations in the fields. The following values are achieved: The temperature setting in the range 1.7-400 K varies less than 0.5% for 10 min, which is the typical recording time of a spectrum. The distance from the NMR oscillator to the sample is only 55 cm (wavelength of approximately 550 MHz radiation), giving a tolerable He evaporation rate of 0.35 l/h. The maximum field at 4.2 K is 43.2 kG, which can be measured with an accuracy better than +/-100 ppm. The homogeneity at maximum field over a central sphere 8 mm in diameter is 5 G. The uncertainty on the crystal orientation in the field is +/-1/2 degree.     

A Peltier cells differential calorimeter with kinetic correction for the measurement of cp(H,T) and Δs(H,T) of magnetocaloric materials

In this paper we describe and test a setup for the characterization of the magnetocaloric effect around room temperature. The setup is a differential calorimeter able to measure both the specific heat c(p)(H,T) under constant magnetic field H and the isothermal entropy change induced by changing H, Δs(H,T), in the room temperature range. The setup uses miniaturized Peltier cells to measure the heat flux, with resolution of about 1 μW, and power Peltier cells to regulate the temperature in the range from 243 K (-30 °C) to 343 K (+70 °C). The kinetic effects due to the heat capacity of the measuring cells are taken into account by a simple model of the heat flux diffusion in the calorimetric cell. As measurement examples, we show the characterization of the magnetocaloric effect in magnetic materials with a second order transition [without latent heat and without hysteresis, as in the La(1)(Fe(1-x-y)Co(y)Si(x))(13) alloy with x=0.077 and y=0.079] and with a first order transitions (with latent heat and hysteresis as in Ni(50)Mn(36)Co(1)Sn(13)). As a result we compare the entropy change Δs(H,T) derived from (i) the integration of the specific heat c(p)(H,T) and (ii) the direct isothermal measurements, obtaining an excellent agreement.     

Compact very low temperature scanning tunneling microscope with mechanically driven horizontal linear positioning stage

We describe a scanning tunneling microscope for operation in a dilution refrigerator with a sample stage which can be moved macroscopically in a range up to a cm and with an accuracy down to the tens of nm. The position of the tip over the sample as set at room temperature does not change more than a few micrometers when cooling down. This feature is particularly interesting for work on micrometer sized samples. Nanostructures can be also localized and studied, provided they are repeated over micrometer sized areas. The same stage can be used to approach a hard single crystalline sample to a knife and cleave it, or break it, in situ. In situ positioning is demonstrated with measurements at 0.1 K in nanofabricated samples. Atomic resolution down to 0.1 K and in magnetic fields of 8 T is demonstrated in NbSe(2). No heat dissipation nor an increase in mechanical noise has been observed at 0.1 K when operating the slider.