The Origin Magnetars: the role of anisotropic neutron superfluid of   neutron stars
  We estimate the strength of the induced magnetic field due to the total induced magnetic moment of the anisotropic ($^3PF^2$) neutron superfluid interior of neutron stars. The induced magnetic field of the neutron stars is found as follows. $B^{(in)} = \frac{\eta}{{T_7 - \eta}}B^{(0)} ,\begin{array}{*{20}c}{} & {\eta =} \ \end{array}\frac{{m(^3 P_2 )}}{{0.1m_{Sun}}}R_{NS,6}^{- 3} $ ($T_7$ denotes the interior temperature of the neutron star in unit of 10$^7$ K). The induced magnetic field will gradually increase with the temperature of the neutron star decreasing in their late evolutionary stage. A magnetar may appear in a condition when $T_7 \to \eta$. The upper limit of the induced magnetic field of $^3P^2$ superfluid is $3.35 \time 10^{14} \eta$. 
Qiu-he Peng