Magnetic Structure-Dependent Ultrafast Spin Relaxation in Magnet CrI: A Time-Domain ab Initio Study.

Two-dimensional magnet CrI is a promising candidate for spintronic devices. Using nonadiabatic molecular dynamics and noncollinear spin time-dependent density functional theory, we investigated hole spin relaxation in two-dimensional CrI and its dependence on magnetic configurations, impacted by spin-orbit and electron-phonon interactions. Driven by in-plane and out-of-plane iodine motions, the relaxation rates vary, extending from over half a picosecond in ferromagnetic systems to tens of femtoseconds in certain antiferromagnetic states due to significant spin fluctuations, associated with the nonadiabatic spin-flip in tuning to the adiabatic flip. Antiferromagnetic CrI with staggered layer magnetic order notably accelerates adiabatic spin-flip due to enhanced state degeneracy and additional phonon modes. Ferrimagnetic CrI shows a transitional behavior between ferromagnetic and antiferromagnetic types as the magnetic moment changes. These insights into the spin dynamics of CrI underscore its potential for rapid-response spintronic applications and advance our understanding of two-dimensional materials for spintronics.