Multidomain Interactions in Perpendicular Magnetic Tunnel Junction (p-MTJ): Enabling Multistate MRAM

We present a comprehensive study of multidomain (MD) effects in a perpendicular magnetic tunnel junction (p-MTJ). The MD nucleation is considered in the free layer of MTJ, which alters the spatial net-magnetic field (
${H}_{\text {eff}}$
) and magnetization vector (
${M}_{e}$
). These variations in
${H}_{\text {eff}}$
and
${M}_{e}$
cause a reduction in the field-like and spin-transfer torques. Furthermore, due to the increased inertia, the switching probability of the MD state is smaller than that of the mono-domain state. We also show that MD formation in the free layer leads to multistate storage in a single MTJ device. We observe a trade-off between the device’s multistate storage and tunnel magnetoresistance (TMR) ratio: an enhancement in the multistate leads to a reduction in the TMR ratio. MD texture in the free layer is obtained by the coupled solution of 2-D Poisson’s equation with the ferromagnetic net energy state equation (MD demagnetization energy + exchange energy + Dzyaloshinskii–Moriya interaction (DMI) + Zeeman energy + anisotropy energy). Following that, the MD switching characteristics are captured by plugging
${H}_{\text {eff}}$
and
${M}_{e}$
into the Landau–Lifshitz–Gilbert (LLG) equation. Our work opens a new era of MD dynamics in the MTJ, which can be utilized to realize an efficient multistate magnetic random access memories (MRAM).