Answer:
The dominant theory of the strong fields of magnetars is that it results from a magnetohydrodynamic dynamo process in the turbulent, extremely dense conducting fluid that exists before the neutron star settles into its equilibrium configuration.
How strong is a magnetar magnetic field?
It can generate the most intense magnetic field observed in the Universe. The field strength of a magnetar is one thousand trillion times stronger than Earth's and is so intense that it heats the surface to 18 million degrees Fahrenheit. We only know of about 10 magnetars in the Milky Way galaxy.