A Vibrating Reed Magnetometer for Microscopic Particles
01 Aug 1970-Review of Scientific Instruments (American Institute of Physics)-Vol. 41, Iss: 8, pp 1241-1243
About: This article is published in Review of Scientific Instruments.The article was published on 1970-08-01. It has received 70 citations till now. The article focuses on the topics: Magnetometer.
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TL;DR: In this paper, the authors describe a type of vibrating-sample magnetometer capable of sensitivity exceeding 10−8 emu, which is 1000 times more sensitive than a conventional VSM with comparable working space, and is much quicker to use than a SQUID magnetometer which generates point-by-point data.
Abstract: This paper describes a type of vibrating‐sample magnetometer capable of sensitivity exceeding 10−8 emu. The instrument is 1000 times more sensitive than a conventional VSM with comparable working space, and is much quicker to use than a SQUID magnetometer, which generates point‐by‐point data. The magnetic sample is mounted on the end of a cantilevered rod that incorporates a piezoelectric element. The sample is magnetized by a dc field (variable in magnitude), and is simultaneously subjected to a small alternating field gradient. The alternating field gradient exerts an alternating force on the sample, proportional to the magnitude of the field gradient and to the magnetic moment of the sample. The resulting deflection of the cantilever rod is measured by the voltage output of the piezoelectric element. By operating at or near a mechanical resonance frequency of the cantilever, the output signal is greatly amplified. In practice, the operating frequency is 100–1000 Hz, with mechanical Q values of 25–250. Mechanical and acoustic noise in the environment limits the sensitivity. Measurements have been made with a signal‐to‐noise ratio of about 500 on a 25‐μm sphere with a moment of 3.7×10−6 emu; this corresponds to a sensitivity of at least 10−8 emu. A complete hysteresis loop over ±10 kOe can be made in about 100 s. Measurements have been made over a temperature range from 77 to 400 K.
180 citations
TL;DR: In this article, the authors follow the path of the magnetic nanostructure and explain some of the steps along the way: What are the technologies that employ magnetic nano-structures? How these nanostructures made? What is the physics behind the functional parts? How are the magnetic properties measured?
Abstract: Magnetic nanostructures are an integral part to many state-of-the-art and emerging technologies. However, the complete path from parts (the nanostructures) to the manufacturing of the end products is not always obvious to students of magnetism. The paper follows this path of the magnetic nanostructure, and explains some of the steps along the way: What are the technologies that employ magnetic nanostructures? How are these nanostructures made? What is the physics behind the functional parts? How are the magnetic properties measured? Finally, we present, in our view, a list of challenges hindering progress in these technologies.
119 citations
TL;DR: In this paper, a detailed discussion of the magnetic properties of soft and hard ferromagnetic materials relevant for electromagnetic applications is given, and a brief consideration is given to the special problems posed by measurements on feebly magnetic materials.
Abstract: Major methods to measure the magnetic properties of materials are systematically discussed in the light of the general phenomenology of magnetism in matter and its physical interpretation. Attention is paid to the problems of measurement traceability and reproducibility and the related standards. While the discussion is focused on the characterization of the soft and hard ferromagnetic materials relevant for electromagnetic applications, brief consideration is given to the special problems posed by measurements on feebly magnetic materials. It is stressed how geometrical and physical properties can often combine to make the determination of the true magnetic properties of materials a somewhat elusive goal. Measurement reproducibility can nevertheless be attained under the guidance provided by written standards. Recent evolution of the magnetic measuring techniques has occurred in response to the digital revolution and the development of novel high-performance materials (e.g. extra-hard rare-earth based magnets, multilayers, micro/nanostructures, etc). It is stressed, however, that the drive to progress in measurements ultimately stems from the search for new fundamental phenomena in materials and their understanding.
78 citations
TL;DR: In this paper, a relation between the reversible susceptibility χ of the minor loops and the coercivity Hc has been found, showing that the investigated material is determined by the pinning of domain walls, rather than nucleation.
Abstract: Measurements of minor loops of SmCo5 powders have revealed that wall motion is predominant in the magnetization process. A relation between the reversible susceptibility χ of the minor loops and the coercivity Hc has been found, showing that the coercivity of the investigated material is determined by the pinning of domain walls, rather than nucleation. The relation χHc2 = constant has been found in a wide range of coercivities obtained by aging of the material. The aging process is interpreted as a decrease of the density of pinning sites, each site retaining its pinning force. The influence of hydrogen on Hc, which is reported recently, is interpreted likewise. A hysteresis loop measured on a single particle of a few microns size confirms these interpretations and allows for a refined model of pinned‐wall coercivity of SmCo5 powders. A full account will be submitted as a regular article to this Journal.
68 citations
TL;DR: In this article, the authors present a series of successive procedures, by which experimental hysteresis and back-field magnetization data are ultimately converted into hyperbolic spectra.
Abstract: SUMMARY The new rock-magnetic method presented here is a series of successive procedures, by which experimental hysteresis and back-field magnetization data are ultimately converted into ‘hyperbolic spectra’. The processing comprises smoothing and centring of raw data, asymptotic slope correction, determination of common hysteresis parameters and modelling of induced and remanent hysteresis components with specially adapted hyperbolic basis functions. The resulting spectral diagrams denote the relative contributions of 10-40 coercivity classes, each representing ferromagnetic particles of a narrow, clearly defined coercivity range. The distribution patterns of these spectra allow the discrimination and quantification of discrete mineral or grain-size fractions and the calculation of their partial hysteresis loops. A computer program (‘HYSTEAR’) for interactive and automated hysteresis loop data processing applying the algorithms described is available from the author.
68 citations
References
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TL;DR: In this article, the magnetization jumps were investigated in a single particle, and it was found that they occurred at various reproducible and strongly quantized fields, whose value depended on the value of the field previously applied to saturate the sample.
Abstract: A new technique for the separation of strongly magnetic powders by particle size has led to observations of discontinuous magnetization changes in samples of cobalt-rare-earth particles. These magnetization jumps were investigated in a single particle, and it was found that they occurred at various reproducible and strongly quantized fields, whose value depended on the value of the field previously applied to saturate the sample. This suggested that the coercive force of these materials might be very sensitive to the nature of the surface, which was verified experimentally. These results add support to the interpretation of the magnetic properties of high-crystal-anisotropy permanent magnet materials in terms of domain boundary nucleation and motion.
49 citations
TL;DR: In this article, a method for measuring the diamagnetic or paramagnetic susceptibilities of small particles of diameters of 1 to 100 μ is described, and theoretical considerations for the design of the apparatus and for the interpretation of measurements are given.
Abstract: A method for measuring the diamagnetic or paramagnetic susceptibilities of small particles of diameters of 1 to 100 μ is described. Theoretical considerations are given for the design of the apparatus and for the interpretation of measurements. Susceptibility determinations of polystyrene latexes and red blood cells show the use of the method.
35 citations
TL;DR: In this paper, the construction and principle of operation of a new type of quartz fiber torsion balance are described, which enables magnetic measurements to be made on an individual microscopic magnetic particle of about 1μ diameter.
Abstract: The construction and principle of operation of a new type of quartz fiber torsion balance are described. The quartz suspension fiber used can be as small as 0.5‐μ diameter. This enables magnetic measurements to be made on an individual microscopic magnetic particle of about 1‐μ diameter.
12 citations