Contents I. Introduction
The need to measure the high-frequency permeability of magnetic materials and magnetic thin film has increased due to using the fifth-generation mobile communication system, spintronic devices, and so on. Many methods have been reported for evaluating the high-frequency magnetic permeability of magnetic materials [1], [2], [3], [4]. On the other hand, high-frequency magnetic materials, such as ferrite used at high frequencies, are actually thick samples (usually over m in thickness). Generally, thick magnetic samples require the error reduction of the demagnetizing field. The Nicolson-Ross–Weir (NRW) method using coaxial structure has a closed toroidal loop [4]. The magnetic closed-loop eliminates the demagnetizing field inside the magnetic material to evaluate permeability; therefore, no error from the demagnetizing field is generated in principle. However, the sample size and frequency band are strictly limited. Recently, we developed an ultrabroadband microstrip line-type probe for measuring permeability and permittivity up to 67 GHz [5], [6]. However, since thick magnetic materials are placed close to the microstrip line conductor, the perpendicular components of the magnetic field were not ignored. Therefore, the permeability was observed to be lower, and the ferromagnetic resonance frequency was higher due to the demagnetizing field [7]. Thus, this study aims to eliminate the measurement error of the demagnetizing factor.
