  The long-range spin-triplet supercurrent transport is an interesting
phenomenon in the superconductor/ferromagnet ($S/F$) heterostructure containing
noncollinear magnetic domains. Here we study the long-range superharmonic
Josephson current in asymmetric $S/F_1/F_2/S$ junctions. It is demonstrated
that this current is induced by spin-triplet pairs
$\mid\uparrow\uparrow\rangle-$$\mid\downarrow\downarrow\rangle$ or
$\mid\uparrow\uparrow\rangle+$$\mid\downarrow\downarrow\rangle$ in the thick
$F_1$ layer. The magnetic rotation of the particularly thin $F_2$ layer will
not only modulate the amplitude of the superharmonic current but also realise
the conversion between
$\mid\uparrow\uparrow\rangle-$$\mid\downarrow\downarrow\rangle$ and
$\mid\uparrow\uparrow\rangle+$$\mid\downarrow\downarrow\rangle$. Moreover, the
critical current shows an oscillatory dependence on thickness and exchange
field in the $F_2$ layer. These effect can be used for engineering
cryoelectronic devices manipulating the superharmonic current. In contrast, the
critical current declines monotonically with increasing exchange field of the
$F_1$ layer, and if the $F_1$ layer is converted into half-metal, the
long-range supercurrent is prohibited but $\mid\uparrow\uparrow\rangle$ still
exists within the entire $F_1$ region. This phenomenon contradicts the
conventional wisdom and indicates the occurrence of spin and charge separation
in present junction, which could lead to useful spintronics devices.
