MicroMag™ MAGNETOMETER SYSTEMS

        First, a word about measurement system speed and sensitivity.  Speed and sensitivity are perhaps the most important elements of any measurement.  In the case of weak magnetic samples, signal averaging is employed to trade speed for sensitivity.  Unfortunately, extravagant claims of sensitivity may make it difficult to compare various measurement techniques, or even different implementations of the same technique.

        Sensitivity can only be characterized by an objective, quantitative measure of system noise:  Standard deviation of the measured quantity over a given averaging time.  It is important to note that the practical lower limit of sample moment is many times greater than standard deviation.  As a rule-of-thumb, "peak-to peak" noise is of the order of five times standard deviation (quotation marks are included because the term "peak-to-peak" is without  meaning when dealing with statistical variables).  Even where the sample moment may be five times standard deviation, the resultant signal-to-noise would not permit estimation of magnetic moment with any degree of accuracy.

        In both the AGM and VSM, sensitivity is related to the dimensions of the measurement volume.  Sensitivity can be improved by reducing the size and spacing (that is, by reducing the magnet gap) of the VSM pickup coils, or the AGM gradient coils.  Of course, there are penalties associated with this approach:  the size of sample that can be accommodated is smaller, and the corresponding reduction in moment may outweigh the improved sensitivity.  Even where the sample can be accommodated, however, measurement accuracy is sacrificed where the sample dimensions are significant vis-a-vis the dimensions of the pickup coil/gradient coil assembly.

        A further consideration involves what might be termed "dead time".  Some implementations necessarily require a pause to be inserted between stepping the magnetic field and commencing the averaging interval.  For a given measurement time this "dead time" directly subtracts from the averaging time, adversely (and significantly) affecting signal-to-noise.

        In the final analysis, different measurement systems can only be compared by measurements of particular samples under similar conditions.  Princeton Measurements Corp. stands ready to perform such measurements.

WHICH SYSTEM IS BEST FOR YOUR APPLICATION:

     MicroMag™ Magnetometers are fast, sensitive magnetic measurement systems which provide the user with convenient easy to use tools for analyzing the magnetic properties of varying materials.  Our systems incorporate two of the basic magnetometer measurement techniques with overlapping functional capabilities.   The two techniques are represented by our alternating gradient and vibrating sample magnetometers and the following information is intended to assist the user in determining which system best suites his or her application.

     It is important to note here that BOTH TECHNIQUES are available only from Princeton Measurements Corporation and can be supplied either separately or as a combination system.  It is also possible to purchase a system based on one technique and later, add the other capability utilizing much of the original hardware purchased.  The operating software is compatible with both techniques.

    While both techniques provide much the same data, the optimum measurement technique depends upon the materials physical and geometric characteristics, the environmental range in which the measurements are to be made and the expected magnetic properties of the material to be evaluated.  The following table lists some of the specifications for our alternating gradient and vibrating sample magnetometer systems and can be used to help identify the optimum technique based upon the users requirements.

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