Element-specific XMCD hysteresis loops in iron oxides nanoparticles and thin films

P. MENDOZA ZÉLIS ; G. PASQUEVICH; C.E. RODRIGUEZ TORRES

Buenos Aires

Congreso; Latin American Workshop on Magnetism, Magnetic Materials and their Applications; 2013

Centro nacional de energía atómica - Universidad de Buenos Aires

There exist several techniques to measure the magnetic properties of materials. Most of them are sensitive to the total magnetization of the measured system and cannot discern among the contributions of non-equivalent atomic sites. X-ray Magnetic Circular Dichroism (XMCD) is a synchrotron-based technique that allows element-selective magnetic properties to be obtained. XMCD is the difference between two x-ray absorption spectra (XAS) taken in a mag- netic field, one taken with left circularly polarized light, and one with right circularly polarized light; which effectively measures the populations of the up and down spin orientations. XMCD is measured at the XAS edge of a specified element in a sample, which enables element-selective measurement. The intensity of XMCD is proportional to the mean magnetic moment projected onto the direction of the incident X-ray, and the sign of the intensity reveals the direction of the probed moment in relation to that of the total magnetization. Since contributions of Fe3+ on octahedral and tetrahedral sites in spinel structure are clearly distinguishable from each other in XMCD signals, hysteresis loops for each iron site can be obtained measuring the x-ray absorption as a function of the magnetic field intensity at different characteristic energies. In this work, we present XMCD hysteresis loops taken at the Fe L-edge in maghemite nanoparticles and in Zn ferrite nanoparticles and thin films. XMCD hysteresis loops were measured using the total electron yield mode at Brazilian Synchrotron Light Laboratory (PGM beamline). Our results will be compared with hysteresis loops taken by means of a vibrating sample magnetometer under the same conditions.