Study of slow magnetization relaxation in Hf/GdFeCo/SiN Hall bar by anomalous Hall resistance measurements

•Magnetization relaxation in Hf/GdFeCo/SiN as a function of current polarity, probe widths, and notch in the device.•In notched Hall bar, the smaller HC for positive current seems due to valve-like behavior from notch.•Notch provides smaller delays for nucleation and switching compared to the no-notch Hall bar.•Narrow probe shows the advantage of comparatively faster and less stochastic switching.•Sense current is another important key to controlling the nucleation delay.