Very Low Frequency Integrating Vibrating Sample Magnetometer (VLFVSM) with High Differential Sensitivity in High dc Fields

Abstract

A vibrating sample magnetometer is described which is specifically adapted for magnetic moment measurements in high dc fields. The sample is moved at very low frequencies between series opposing detection coils, the induced voltage is integrated, and each cycle is recorded so that the output can be further time-averaged. Two novel aspects make this instrument particularly useful for high field measurements. First, the sample is moved beyond the center of the detection coils so that positioning errors, forces, and other incidental effects are eliminated. Second, a precise reference balance voltage is synchronously applied to the output signal to permit high-resolution differential measurements of magnetic moment. In addition to a detailed description of the basic VLFVSM, a general discussion of flux integration techniques is presented. Operation of the VLFVSM with field modulation superimposed, variable temperature, variable pressure, additional electronic filtering, and under swept-field conditions is discussed. Mechanical and electronic details and typical operating characteristics are included. The entire magnetometer has moderately high sensitivity, is extremely rugged, versatile, and eliminates sources of error present in many sample extraction techniques. All components, excluding the mechanical systems associated with the sample, are available commercially. This magnetometer has been applied to practically all types of high field magnetic moment measurements including differential susceptibility measurements in metals, alloys and insulators, superconductors, and highly anisotropic materials such as the rare earth metals.