  We conduct an experimental study of high-mobility two-dimensional electron
gas (2DEG) in GaAs/AlGaAs quantum wells modulated by strong magnetism at an
in-plane magnetic field ($B$). The modulated $B$-fields are performed via the
single stripe and gratings which are made of the heavy rare earth metal Terbium
(Tb) thin films on the sample surface. The robust ferromagnetic resonances
(FMRs) persist to the temperature of 50-70 K in both the stripe and grating
samples, for the ferromagnetism (FM) phase of Tb exists at above 100 K. The
high-order (with integer numbers of $j \equiv \hbar\omega/g\mu_{B}B = 1,
2,$...) magnetic resonances can also be observed in the stripe structure via
the microwave (MW) photovoltaic detection and magnetoresistance under microwave
irradiation. In addition, the resonance features around $j = 1/2$ are robust in
the single-stripe modulated sample, which suggests the spinons with spin-1/2
collective excitations in a 1D Heisenberg model.
