Continuous Real Time Field Control in Magnetic Measurement Systems

Regulating the field characteristics of magnetic materials is a critical parameter to be considered during the research, development and manufacture of magnetic materials.

Even a slight deviation in the coercive field of the magnetic materials may affect the effectiveness of the material. The coercivity, in certain materials is measured in mOe. A real-time field control integrated system is well-suited for obtaining accurate measurements.

MicroSense has developed magnetic measurement systems combined with real-time field control technology for applications in production quality control systems and research measurement systems.

Magnetic Field Control in MicroSense Measurement Systems

Most magnetic measurement systems use electromagnets in order to generate an electric field. A typical electromagnet consists of a pair of poles, a yoke and a pair of coils. The poles and yoke are made of a magnetic alloy or magnet iron which behaves non-linearly.

The magnetic field varies with respect to time at a certain current, when the eddy currents disappear and the domain walls in the pole tips start moving.

Traditional measurement systems such as VSMs involve the indirect control of a magnetic field. This is a slow process owing to the communication lag between the power supply response and Gaussmeter.

In recent times, however, many systems have shifted the field control from the PC to a DSP within the field control unit. Although DSP-based systems are faster, they are still an iterative process with a lag in the response.

However, the field control in the MicroSense systems is different from that of other systems. Instead of subroutines, MicroSense systems consist of a specific hardware developed exclusively for fulltime field control.

In addition, an electronic control loop continuously adjusts the magnetic field to maintain it with respect to the set point. The field noise in the MicroSense systems is very low as the field values are not digitized.

Figure 1 shows the measurement of field noise in MicroSense VSM. Real time field control is faster than other field control systems. It was reported that real-time systems are approximately three times faster than the non real-time field control.

Figure 1. Typical measurement of field noise in MicroSense VSM

Experimental results show that the real-time direct field control system enables the user to perform measurements with steps as small as 1mOe, unlike any other type of measurement system.

Dynamic Gauss-Range Change Function

Dynamic Gauss Range Change is a key function of the MicroSense VSM measurement system. It enables the system to switch the Gauss range at the time of application of magnetic field in the middle of a measurement.

Using this function, measurement of hysteresis loop is possible, and the users can obtain the highest resolution field readings during low-field measurements. This helps in the measurement of GMR, MRAM, MTJ and spin-valve samples, generating a M(H) curve which exhibits multiple hysteresis.

This feature enables the user to accurately measure the entire loop without compromising on the saturation of high field sample.

Conclusion

The MicroSense VSM systems have a field resolution 60 times better than most of VSM-based super conducting magnet and 50 times greater than some Helmholtz coil based VSM systems. Figures 2 and 3 show the graph illustrating the measurement of samples using the MicroSense VSM.

Figure 2. Measurement result on a 10 µm micro-wire using MicroSense VSM

Figure 3. Measurement on a sample with a coercivity of 4mOe

About MicroSense

MicroSense, LLC, previously known as ADE Technologies, is comprised of three primary businesses – precision capacitive sensors, vibrating sample magnetometers and magneto-optical Kerr effect (MOKE)tools for state-of-the-art magnetic measurement and wafer measurment systems.

Until the company was sold in November, 2009, we were a subsidiary of KLA-Tencor Corporation, a leading global supplier of semiconductor wafer defect inspection and metrology tools. MicroSense serves a host of industries including semiconductor equipment, data storage, machine tool, solar, automotive and high brightness LED. MicroSense provides customer value and security, through extensive business experience, financial strength, world-wide support, and technical leadership.

This information has been sourced, reviewed and adapted from materials provided by MicroSense, LLC.

For more information on this source, please visit MicroSense, LLC.

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