A Recommended Book for A Naive to Learn Material Science

If you are needing to block the magnetic field for an experiment it may be easier to move your experiment to an area free of magnetic fields. Agricultural fields away from power lines are the quietest environment you are likely to find both electrically and magnetically.

Motorola has a million dollar RF absorbing chamber for testing and certifying some equipment one of their competitors uses a corn field.

Gordon

Block as in shield can be done two was, but neither is 100%. Magnetic shielding is easy to find, but what might suit your needs better are to use driven magnetic coils that offset the external fields you want to stop. There are commercial devices available just to do that for stray fields one might get from motors and transformers. If you need to go higher, custom fab coils and supply. Can even track varying field with hall sensors and that's something mu metal can't do.

Dr. K