Magnetic coupling in manganite-based thin film heterostructures studied by Electron Holography

Abstract

Advances in nanofabrication of magnetic nanomaterials leads to search for new tools to measure physical properties at the nanoscale, such as magnetization. Accurate characterization of the magnetization states in nanostructures is of the utmost importance in the development new devices such as magnetic tunnel junctions (MTJs). Transmission electron microscopy (TEM) techniques such as Electron Holography (EH) allows the quantitative imaging of the magnetization states of ferromagnetic materials with unprecedented spatial resolution at the nanometer level. Furthermore, EH can be combined with the in situ variation of external parameters such as magnetic and electric fields, temperature, etc. In particular, we use a TEM cryo-holder to image magnetization states of ferromagnets with low TC (down to 100 K) while varying in situ the magnetic field applied by the objective lens of the TEM. In this work, we present the EH study of the magnetization switching of La-Sr and La-Ca manganite thin films (TC = 180 and 300 K, respectively) and manganite-based MTJs. The (de)coupling of magnetic electrodes in MTJs is analyzed by performing hysteresis loops at 100 K to determine the switching fields from the direct observation of the magnetization orientation o fthe electrodes upon magnetic field.