Development of microscopic magnetometer with reflective objective using magneto-optical Kerr effect

A microscopic magnetometer using magneto-optical Kerr effect (MOKE) was developed to characterize the magnetic properties of hard magnetic nano-structures such as a bit-patterned medium and a magnetoresistive random access memory. Our new type magnetometer has a unique feature that adopts the reflective objective instead of the generally used refractive lens to reduce the unnecessary rotation of polarization axis of the light by the lens with Verdet constant in a magnetic field. A Schwarzschild-type objective consisting of two spherical mirrors was applied as the reflective objective in our magnetometer. The objective was designed specifically for our magnetometer. An actual focusing spot diameter at the sample surface was estimated to be 4.7 mu m by the knife-edge measurement. Furthermore, a magnetization curve was measured by MOKE for the Co80Pt20 thin-film line with a width of 75 mu m, and demonstrated that our magnetometer can reduce the unnecessary rotation of polarization axis compared with the one measured by the magnetometer with a refractive lens. (C) 2012 American Institute of Physics. [doi:10.1063/1.3675176]