  Highly precise pulsar timing is very important for understanding the nature
of neutron stars and the implied physics, even being used to detect directly
gravitational waves. Unfortunately, the accuracy of the pulsar timing is
seriously affected by the spin-down irregularities, such as spin fluctuations
with a manifestation of low frequency structures (the so-called red noise
processes), and various activities of magnetospheres. Except from the random
timing noise, significant periodic or quasi-periodic components could also be
found in some timing residuals of pulsars, indicating the presence of
unmodelled deterministic effects. The physical origins of these effects still
remain unexplained. In this paper, we suggest a new mechanism involving the de
Haas-van Alphen magnetic oscillation, which could trigger the observed low
frequency structures. We find that the proposed magnetic oscillation period is
about 1-$10^{2}$ yr, which is about $10^{-4}$ times as long as the classical
characteristic time scale of interior magnetic field evolution for a normal
neutron star. Due to the magnetic oscillation, we estimate both the braking
index range between $10^{-5}$ and $10^{5}$ and the residuals range between 4 to
906 ms for some specific samples of quasi-periodic pulsars. Those are
consistent with the pulsar timing observations. Nonlinear phenomena of de
Haas-van Alphen effect and the Condon domain structure are considered.
Avalanche-like magnetized process of domain wall motion (rapidly magnetic
energy release) could associated with some special emitting manifestations of
neuron star radiation.
