磁针磁矩的测量和耦合磁针的实验研究

第3届全国大学生物理实验竞赛基础实验题包括3部分:测量磁针处局域磁场水平分量的大小,测量磁针的磁矩和转动惯量以及地磁场中耦合磁针的运动研究.介绍竞赛试题的实验内容并给出解答,分析了参赛学生的实验考试结果.     

对地磁水平分量测量实验的改进

通过地“地磁水平分量测量”实验的改进，介绍一种测量振动周期的新方法，即将小磁针在磁场中的机械振动周期的测量转变为同步的电信号振动周期的测量。     

自制投影用小磁针

奥斯特实验,是教学中的重要演示实验之一,作为演示实验,由于小磁针较小,又在桌面上做实验,故可见度很低,实验观察效果不够理想．笔者自制了透明的小磁针,让实验在投影仪上完成,增大了实验的可见度．如图１所示,取一按扣,留凸扣面,将两对面稍向下弯曲,然后将两个磁化钢针穿过凸扣穿线孔．将透明胶片剪成磁针形状,一方涂红色,另一方涂蓝色,将其中间弄一小孔,将磁化钢针的南北极与胶片颜色对应好,将其扣在凸扣上,自制小磁针就做好了．再取刻写蜡纸的铁笔笔尖,用胶直接粘在放置实验装置玻璃板的合适位置上,做为小磁针支架．…     

信箱

<物理实验>2000年第2期介绍了"自制投影用小磁针"一文,较好地解决了演示实验中,磁针小,可见度低,实验观察效果不理想的问题.在此介绍两种简便易行的方法,供同仁们参考.     

磁针标准样品建立的必要性及其应用

<正> 磁针装置是某些测角仪器的重要部件。在需要定向的光学仪器中均装有磁针。磁针根据磁子午线使仪器定向,即给出磁北,以便仪器测量磁方位角,因此,这类光学仪器的技术条件规定:“仪器的瞄准线应平行于磁子午线,允许差为θ(单位为密位)”。显而易见,仪器测量磁方位角的精度与磁针的定向精度有关。     

地磁场中磁针的耦合运动

通过不同条件下的两种模型研究耦合磁针的运动规律,求解了3种典型初始条件时磁针的运动情况,并做了实验进行验证,对会出现的相关现象加以讨论,加深对耦合现象的理解.     

三维磁针

传统磁针只能在水平方向上转动,很难表示三维空间中磁场的方向.增加一个水平转动轴,磁针就可以在三维空间转动.多个这样的磁针,可以演示三维空间中磁感线的方向.三位磁针的具体做法如图1所示.     

地磁水平分量的测量

用动力学的方法测量了地磁场的水平分量.通过改变电路中电流的大小和方向,测量磁针在地磁场水平分量和外加亥姆霍兹线圈产生的合磁场的共同作用下的简谐振动周期,用作图法得到合磁场为零的电流值,从而得到地磁场水平分量.     

一种演示磁感线的简单方法

在电磁学实验中,用小磁针演示磁感线没有"连续的"效果.笔者采用一种巧妙的办法,使磁感线的演示直观生动,现介绍如下.     

磁传感器与磁场的测量

在中学物理教学中，研究磁场传统的实验方法是用小磁针显示磁场的方向，用小磁针或铁粉显示磁感线分布．磁针和铁粉用来形象描述磁场功不可没，可对磁感强度的定量研究却显得无能为力．学生也只好在题海中领会感受磁感强度B的大小；1特斯拉有多大?在脑子里只有一个模糊抽象的印象．物理学对电磁现象的研究成果为各行各业提供了先进的检测设备，可是在自身的物理教学中对磁场的实验检测仍停留在4大发明的“司南”时代．近来上海的DIS实验(数字化实验系统)，     

奥托·斯特恩对质子磁矩的研究

因为对分子束方法的发展和对质子磁矩的发现,奥托·斯特恩获得了1943年的诺贝尔物理学奖.1933年,斯特恩和他的合作者测量了质子磁矩.质子磁矩的测量,拓展了人类探索微观世界的途径,加速了人们认知核子结构的进程.以文献研究法为主要手段,从质子磁矩测量实验本身展开,深入挖掘了斯特恩等人关于质子磁矩测量工作的全过程,旨在厘清斯特恩等人在质子磁矩测量工作方面的开创性贡献,以及该实验对于20世纪30年代原子核物理学发展的贡献所在.     

Estimation of physical parameters of magnetic nanoparticles

The results of estimation of the magnetic moment and sizes of magnetic nanoparticles in a magnetic fluid obtained using the technique based on measuring the field dependence of the acoustomagnetic effect are considered in the paper. The samples with different magnetic phase concentrations are analyzed. The obtained results compared with the data of magnetogranularmetric analyses are studied.     

Revelation of Ni magnetic moment in GdNi single crystal by soft X-ray magnetic circular dichroism

Magnetic moment of Ni in GdNi single crystal was studied through the soft X-ray absorption spectra (XAS) and the magnetic circular dichroism (MCD) at the Ni L_2,3-edges and the Gd M_4,5-edges. Our experiment revealed for the first time that the Ni 3d band is not filled completely even at the content of 50 at.% of Gd and the Ni does retain a total magnetic moment coupling antiparallel to that of Gd. This result implied that the Ni in GdNi holds an intrinsic magnetic moment even at 50 at.% of Gd and contradicts the well-known charge transfer model. Further by employing the magneto-optical sum rule, the spin and orbital angular magnetic moment were evaluated and discussed.     

铁单质薄膜磁致伸缩行为与磁矩演化研究

磁致伸缩材料在传感器、位移器件等领域应用前景广阔,对此类材料的制备与实验已成为研究热点,但使用分子动力学方法模拟其磁致伸缩过程中内部磁矩的演化仍缺乏相关研究.本研究以磁致伸缩材料铁单质为研究对象,采用分子动力学方法建立单畴铁单质磁致伸缩模型.分析了铁单质薄膜磁致伸缩行为随初始磁矩的变化,以及在磁场作用下微观原子磁矩的变化与宏观磁致伸缩之间的关系.结果表明:模型磁化构型的演化与磁致伸缩行为有着密切联系,随着外加磁场强度增大,原子磁矩与外加磁场方向相同的区域面积逐渐增大,宏观表现为模型的磁致伸缩随磁场强度增大而伸长,并最终达到饱和,而边界处的原子磁矩是模型是否达到饱和磁致伸缩的关键.     

Direct measurement of the proton magnetic moment

The proton magnetic moment in nuclear magnetons is measured to be μ(p)/μ(N) ≡ g/2 = 2.792?846 ± 0.000?007, a 2.5 parts per million uncertainty. The direct determination, using a single proton in a Penning trap, demonstrates the first method that should work as well with an antiproton (p) as with a proton (p). This opens the way to measuring the p magnetic moment (whose uncertainty has essentially not been reduced for 20 years) at least 10(3) times more precisely.     

Giant magnetic moment at open ends of multiwalled carbon nanotubes

The attractions of cantilevers made of multiwalled carbon nanotubes(MWNTs)and secured on one end are studied in the non-uniform magnetic field of a permanent magnet.Under an optical microscope,the positions and the corresponding deflections of the original cantilevers(with iron catalytic nanoparticles at the free end)and corresponding cut-off cantilevers(the free ends consisting of open ends of MWNTs)are studied.Both kinds of CNT cantilevers are found to be attracted by the magnet,and the point of application of force is proven to be at the tip of the cantilever.By measuring and comparing deflections between these two kinds of cantilevers,the magnetic moment at the open ends of the CNTs can be quantified.Due to the unexpectedly high value of the magnetic moment at the open ends of carbon nanotubes,it is called giant magnetic moment,and its possible mechanisms are proposed and discussed.     

Neutrino oscillation and magnetic moment from \nu - e^{-} elastic scattering

We discuss how the measurement of the elastic cross section at reactor energies can be used to extract new information on the neutrino oscillation parameters. We also consider the magnetic moment contribution and show how both effects tend to cancel each other when the total cross section is measured. To achieve the separation of each of the effects, experiments capable of measuring angular and energy distributions with respect to the outgoing electron become necessary. The sensitivity of these kind of experiments to magnetic moments, masses and mixings is discussed. We also discuss the possibility of measuring the magnetic moment of neutrinos via oscillation. Received: 12 September 1997 / Revised version: 22 December 1997 / Published online: 10 March 1998     

Development of measuring magnetic Compton profiles by grazing incidence geometry

A novel technique of measuring a magnetic Compton profile using the grazing angle geometry against a sample surface (Grazing Incidence Magnetic Compton Profile) has been successively developed. Measurements of a magnetic moment and a magnetic Compton profile are possible for a Fe 200 nm film on a thick glass substrate. The estimated thinnest limit for measurements is 100 nm for a Fe film.     

Low-frequency complex magnetic susceptibility of magnetic composite microspheres in colloidal dispersion

A procedure is presented to determine the permanent magnetic dipole moment of composite microspheres containing magnetic nanoparticles with a blocked magnetic dipole moment. The composite particles are dispersed in a solvent, and the complex magnetic susceptibility is measured from 0.1 to 1000 Hz using a highly sensitive new setup. Composite particles with a permanent magnetic dipole moment are revealed by a characteristic frequency that corresponds to the Brownian rotation of the microspheres. From measured susceptibility spectra, we calculate the permanent magnetic dipole moment of recently developed cobalt ferrite-doped silica and latex microspheres.     

光磁共振实验测量gF值方法的改进与拓展

分析了光磁共振实验测量gF值中传统方法存在的问题，提出了利用光抽运信号的变化来判断合磁场方向的改进措施，避免了实验过程中对合磁场的方向和大小的误判以及光抽运信号与共振信号的混杂．同时，拓展了原有的测量方法，丰富了实验内容．