High precision metrology based microwave effective linewidth measurement technique

A precision microwave effective linewidth measurement technique for magnetic samples has been developed. The measurement utilizes a high- Q cylindrical cavity that contains the sample of interest, a highly stable and programable static magnetic field source, a computer controlled network analyzer for cavity center frequency ω c and quality factor Q c determinations, and the standard metrological substitution A B A method for accurate relative ω c and Q c measurements. Sequential long term A B A measurements show that the time and temperature drifts and random errors are the dominant sources of error, with uncertainties in ω c ∕ 2 π and Q c in the range of 50 kHz and 25, respectively. The A B A method is applied to eliminate these drifts and minimize the random errors. For measurements over 25 A B A cycles, accuracy is improved to 0.14 kHz for ω c ∕ 2 π and 3 for Q c . The temperature variation over a single A B A cycle is generally on the order of 10 − 3 – 10 − 5 ° C and there is no need for any further temperature stabilization or correction measures. The overall uncertainty in the 10 GHz effective linewidth determinations for a 3 mm diam, 0.5 mm thick polycrystalline yttrium iron garnet (YIG) disk is 0.15 Oe or less, well below the intrinsic single crystal YIG linewidth. This represents a factor of 10 improvement in measurement accuracy over previous work.