Interface and temperature dependent magnetic properties in permalloy thin films and tunnel junction structures

A short-circuited coplanar waveguide for low-temperature single-port ferromagnetic resonance spectroscopy setup to probe the magnetic properties of ferromagnetic thin films

A coplanar waveguide shorted in one end is proposed, designed, and implemented successfully to measure the properties of magnetic thin films as a part of the vector network analyzer ferromagnetic resonance (FMR) spectroscopy setup. Its simple structure, potential applications, and easy installation inside the cryostat chamber made it advantageous especially for low-temperature measurements. It provides a wide band of frequencies in the gigahertz range essential for FMR measurements. Our spectroscopy setup with a short-circuited coplanar waveguide has been used to extract the Gilbert damping coefficient and effective magnetization values for standard ferromagnetic thin films, such as Permalloy (Py) and Cobalt (Co). The thickness and temperature-dependent studies of those magnetic parameters have also been done here for the afore-mentioned magnetic samples.

Experimental Investigation of Temperature-Dependent Gilbert Damping in Permalloy Thin Films

The Gilbert damping of ferromagnetic materials is arguably the most important but least understood phenomenological parameter that dictates real-time magnetization dynamics. Understanding the physical origin of the Gilbert damping is highly relevant to developing future fast switching spintronics devices such as magnetic sensors and magnetic random access memory. Here, we report an experimental study of temperature-dependent Gilbert damping in permalloy (Py) thin films of varying thicknesses by ferromagnetic resonance. From the thickness dependence, two independent contributions to the Gilbert damping are identified, namely bulk damping and surface damping. Of particular interest, bulk damping decreases monotonically as the temperature decreases, while surface damping shows an enhancement peak at the temperature of ~50 K. These results provide an important insight to the physical origin of the Gilbert damping in ultrathin magnetic films.