Strong magnetic field gradients can produce a synthetic spin-orbit interaction that allows high-fidelity electrical control of single electron spins. We investigate how a field gradient impacts the spin relaxation time $T_1$ by measuring $T_1$ as a function of the magnetic field $B$ in silicon. The interplay of charge noise, magnetic field gradients, phonons, and conduction-band valleys leads to a maximum relaxation time of $160\mathrm{ms}$ at low fields, a strong spin-valley relaxation hotspot at intermediate fields, and a $B^4$ scaling at high fields. $T_1$ is found to decrease with increasing lattice temperature as well as with added electrical noise. In comparison, samples without micromagnets have a significantly greater $T_1$.

• Received 2 November 2018
• Revised 24 March 2019

DOI:https://doi.org/10.1103/PhysRevApplied.11.044063