Long-Lived Ultrafast Spin Precession in Manganese Alloys Films with a Large Perpendicular Magnetic Anisotropy

Spin precession with frequencies up to 280 GHz is observed in Mn_3-δGa alloy films with a perpendicular magnetic anisotropy constant Kᵤ~15 M erg/cm³. The damping constant α, characterizing macroscopic spin relaxation and being a key factor in spin-transfer-torque systems, is not larger than 0.008 (0.015) for the δ=1.46 (0.88) film. Those are about one-tenth of α values for known materials with large Kᵤ. First-principles calculations well describe both low α and large Kᵤ for these alloys.