Measuring the Saturation Magnetization in Samples With Unknown Magnetic Volume

We present a method to determine the saturation magnetization of samples for which the magnetic volume is unknown and thus cannot be calculated from the magnetic moment. This can happen, e.g., in multilayers, where the spacer material is likely to cause intermixing or whenever ion irradiation is used to modify the magnetic properties of samples on purpose. In both cases the effective magnetic volume is altered from its nominal value in an unknown manner. Therefore magnetometry like superconducting quantum interference devices (SQUID) or vibrating sample magnetometry (VSM) fail, because they detect the magnetic moment but do not provide information on the respective magnetic volume. We show, how ferromagnetic resonance (FMR) can be used instead to circumvent this problem. As a test system we have used thin films of permalloy (Py) and Py/Ta multilayers. Some of the Py/Ta samples were irradiated with Ne ions in order to modify the magnetic properties by altering the interface due to intermixing.