Because the needle of a compass is magnetised, it's attracted to the magnetic pole – the points near the North and South Poles where the Earth's magnetic field is concentrated.
The iron atoms each behave as tiny magnets but, whereas in a normal lump of magnetised metal their north-south poles all point in the same direction, in a spin glass they do not.
A magnetic field is used to magnetise the substance creating a magnetic material that can be printed into any shape And, the direction of the magnetic field can be changed during printing.