A focused magneto-optical Kerr magnetometer for Barkhausen jump observations

We describe a modified version of a magneto-optical Kerr magnetometer which allows measuring the hysteresis loop of a specific portion of the sample s urface. The diameter of the sampled area can be optically tuned from severa l mm down to 15 mu m. High quality hysteresis loops can be measured in a fe w seconds. Strong fluctuations are observed when the spot diameter is reduc ed to a few hundred microns or less. These fluctuations are related to the well-known Barkhausen noise here investigated for the first time in a syste matic way using optical techniques. Preliminary data for epitaxial Fe grown on MgO are presented. (C) 2000 American Institute of Physics. [S0034-6748( 00)01904-3].