Simple determination of Curie temperature using a smartphone magnetometer

The Curie temperature, also called the Curie point, is the temperature at which magnetic material undergoes a phase transition from ferromagnetic to paramagnetic properties. The characteristics of permanent magnets appear below the Curie temperature—below 400 °C (673 K) for commercial ferromagnetic materials such as ferrite or neodymium. In ferromagnetic materials, atomic magnets are spontaneously oriented in the same direction in each microscopic domain (crystal region), resulting in a strong magnetic field. Raising the temperature of ferromagnetic materials to the Curie point will interfere with various spontaneous arrangements, and only the weak type of magnetization remains, called paramagnetic. The common method for ascertaining Curie temperature is by using a pendulum Curie point, or using a small magnet attached to a horizontal ferromagnetic wire. The pendulum or ferromagnetic wire, which is heated through combustion or electric heating, will turn into paramagnetic material when it reaches the Curie temperature, so that the pendulum or magnet will fall. The magnet/wire heating method allows the quantitative determination of Curie temperature, with a quite complex measurement and calculation parameters. Therefore, our study focused on demonstrating the Curie temperature of the ferromagnetic material (permanent magnet) quantitatively using a smartphone magnetometer. Measuring and analyzing the magnetization vs. temperature relationship of ferromagnetic material is carried out using the mean field theory (Ising model) approach, so that the Curie temperature of permanent magnets can be easily determined.