  Using a multi-conduction-channel model, we redefined the micromechanism of
spin Hall magnetoresistance (SMR). Four conduction channels are created by spin
accumulation of nonpolarized electron flow at top, bottom, left and right
interfaces of the film sample, which corresponds to different resistance states
of polarized electron flow with various spin directions relative to the applied
magnetic field ($\mathbf{H}$), and brings about the SMR effect finally. The
magnetic insulator layer, such as yttrium iron garnet (YIG), is not a requisite
for the observation of SMR. Instead, the SMR effect is perfectly realized, with
an order of magnitude increase, in the sample with a discontinuous layer of
isolated-Co$_2$FeAl (0.3 nm) grains covered by 2.5-nm-thick Pt layer on MgO
substrate. The model intuitively gives the typical relationship of SMR effect,
i.e. $\rho_{\parallel}\approx\rho_{\bot}>\rho_{T}$, where $\rho_{\bot}$,
$\rho_{\parallel}$ and $\rho_{T}$ are longitudinal reisitivities with applied
magnetic field ($\mathbf{H}$) direction perpendicular to the current direction
out of plane (as Z direction), parallel with and perpendicular to it in plane
(as X and Y direction), respectively. Our research reveals that the scattering
between polarized and nonpolarized conduction electrons is the origin of SMR,
and the intrinsic SMR is not constant when $\mathbf{H}$ direction rotates in XZ
plane, which is distinct from that in the reported SMR mechanism.
