Description

Experimental measurements of electrical signals play an essential role in the development of physical knowledge by the scientific community, being important not only to obtain information about the electromagnetic characteristics of the analyzed material, but it can also be used for mechanical and optical analysis. With the advancement of technology, especially in the area of condensed matter physics, the need to study smaller materials, on the order of micrometers, or even nanometers, has been increasing, and consequently the need for increasingly robust instrumentation.

In the 21st century, the physics of condensed matter involves electrical measurements in orders of magnitude smaller than the noise itself. In the study of magnetism and magnetic properties of materials, the ability to characterize physical effects through this measurement is relevant, such as the magneto-optical Kerr effect (MOKE). This effect describes the change in the polarization angle of light incident on a magnetized surface after its reflection, making it possible to infer properties such as the type of magnetization present in the material, being classified as ferromagnetic, antiferromagnetic or paramagnetic.

In the most used experimental setups, the MOKE measurement is carried out indirectly, through electronic instrumentation equipment, and thus, the difficulty of capturing the signal associated with the physical phenomenon arises. Such an electrical signal is characterized by an amplitude below the noise level, around μV or nV. This signal needs a specific treatment, a usual amplifier would also make the noises amplified and therefore would make the desired analysis difficult. Based on this, the need to build a Lock-in phase-sensitive amplifier becomes significant, since in this type of amplifier it is possible to select and amplify a signal of a desired frequency.

In the present work, a phase-sensitive amplifier (Lock-in) for the MOKE system in longitudinal configuration is made, being possible to evaluate the magnetization behavior in a thin film of IrMn/Py (ferro/antiferromagnetic) as well as the measurement of its exchange bias, through its hysteresis curve.

Key-words: magneto-optical Kerr effect; phase-sensitive amplifier; spintronics; thin films.

Final Report (Portuguese)