This study investigated the formation and relaxation dynamics of nuclear spin polarization in three ${\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ bulk samples with different aluminum concentrations $x$ of 0.00, 0.05, and 0.15. The time-resolved Kerr rotation technique was primarily used. The samples with $x=$ 0.15 and 0.05 exhibited anomalously large nuclear magnetic fields $B_{\mathrm{N}}$ exceeding 1 T, approximately twice the applied magnetic field. Further investigations revealed that $B_{\mathrm{N}}$ formation occurred in two stages: a rapid initial rise followed by a gradual increase toward a saturation value. Relaxation measurements revealed that the relaxation time of $B_{\mathrm{N}}$ was longer for AlGaAs than for GaAs. The comparison of the results obtained under strong and weak magnetic fields indicated the suppression of quadrupole-induced relaxation. We modified the dynamics model of nuclear spin polarization and explained the two-stage formation and the accompanying large $B_{\mathrm{N}}$ in AlGaAs bulks.

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• Magneto-optical Kerr effect
• Magneto-optical spectra
• Nuclear & electron resonance
• Optical transient phenomena
• Spin dynamics
• Zeeman effect
• III-V semiconductors
• Kerr effect