A VERTICAL FORCE ALTERNATING-GRADIENT MAGNETOMETER

A modification of the alternating-gradient magnetometer1 that is especially suitable for measurements above and below room temperature is described. The gradient of the alternating field, and the resulting force on the sample, are made perpendicular to the magnetization direction and a cantilevered piezoelectric sensing element can then be located 10-15 cm above the sample in a constant temperature environment. Under these conditions, the mechanical resonant frequency and gain of the magnetometer are not influenced by changes in sample temperature. The instrument has high sensitivity for measuring small or weakly magnetic samples: a sensitivity of 10- 8 emu/(Hz)1/2 has been obtained over a temperature range from 77 to 700 K. The instrument can also be easily adapted to measure relatively massive or strongly magnetic samples. Samples weighing more than 1 g and magnetic moments above 1 emu have been measured and even higher values could be attained by using heavy piezoelectric elements and extension fibers. Examples of measurements on ferromagnetic, ferrimagnetic, and paramagnetic samples are given, and some practical considerations regarding construction of the instrument and mounting of samples are discussed.