Continuous drift correction and separate identification of ferrimagnetic and paramagnetic contributions in thermomagnetic runs

The principle of a Curie balance was changed by using a sinusoidally cycling applied magnetic field instead of a fixed applied field. This was done with a horizontal translation type Curie balance. By cycling between field values Bmin and Bmax, the output signal is amenable to Fourier analysis. Partial Fourier analysis yields the fundamental harmonic and the second harmonic, termed SIG1 and SIG2 respectively. These are related to the saturation magnetization (Ms) by MS = 2 SIG1 — 8 SIG2 [(Bmax+Bmin)/(Bmax−Bmin)])/[A″(Bmax−Bmin)] and to the paramagnetic susceptibility (χpar) by χpar = 8 SIG2/[A″(Bmax − Bmin)2], whereby A″ is a calibration constant. Through the Fourier analysis continuous drift correction is achieved simultaneously. A personal computer takes care of field control, temperature control and data acquisition in real time mode, as well as processing the data, to yield SIG1 and SIG2. After the experiment, SIG1 and SIG2 are processed further with a separate transversal filtering program that improves the signal-to-noise ratio. The working temperature range of the adapted horizontal translation type Curie balance is between room temperature and 900°C. Its noise level corresponds to a magnetic moment of 2×10−9 Am2, making it a very powerful tool for thermomagnetic analysis of weakly magnetic material. Examples demonstrating this potential of the device are shown.