Voltage spike in MOSFET circuit
When the FET is turned off the current in the inductor has to go somewhere - the diode will start conducting but only after the forward recovery time.  This can be up to 2400ns and a voltage of 2-3v.

The ringing on the purple trace in the last picture is due to inductance in the ground or power leads.

Have you followed my recommendation from your other question regarding a decoupling capacitor between the FET source and the positive end of the inductor?

You need to keep leads very short - with high currents and rapid switching it is important to keep inductances low.