It is related to magnetic field strength h and magnetic induction strength B.
Magnetic energy e magnetic = (1/2)∫ H*B dV.
That is, as long as there is a magnetic field in space, then the magnetic field has energy.
Is equal to the volume fraction of H*B in the whole space divided by 2.
Iron is magnetized, which means that iron can generate magnetic field independently in space.
At this time, this magnetic field obviously has magnetic energy.
However, the energy here is still conserved. This magnetic energy is not given by the magnet, but is excited by the magnet.
Why do you say that?
For ferromagnetic materials, the basic unit of the model is called "magnetic chip", which generates a magnetic field itself, but the magnetic fields of many "magnetic chips" are disordered, so the magnetic fields in all directions are positive and negative and do not display.
When the magnet attracts the iron block, the "magnetic debris" in the iron changes under the action of the external magnetic field of the magnet. The specific changes are very complicated, but the overall effect is that the magnetic field of many "magnetic chips" is strengthened in the direction of the external field and weakened in the opposite direction of the external field.
When the magnet is removed, because the magnetic chip has a certain inertia, it will not immediately return to the original disordered state, so it is still magnetic. This phenomenon is supplemented as "hysteresis phenomenon", and the magnetic field that still exists when the applied magnetic field is zero is called "remanence". This is how iron is magnetized.
As long as there is a magnetic field, there is magnetic energy. It's that simple.
But,
The concept of magnetic energy is always accompanied by space. Because it is volume.
Because the magnetic field lines are closed, in an infinite space, if there is less magnetic field in one direction, there will be more magnetic field in the opposite direction parallel to this direction, so in the whole infinite space, the integral is zero and the magnetic energy is always zero.
However, this does not prevent the existence of the concept of magnetic energy.
Just as it makes sense to sum a finite number of real numbers, but all the real numbers add up to zero, we can't say that the concept of "sum" is useless.
about
What will happen to the magnet if you keep it still and repeat the above process with different iron blocks?
This problem
I can definitely tell you that the magnetic field generated by the magnet will weaken with the passage of time even if the iron block is not used for repetition, because the microscopic particles are doing endless random motion, and the structure in the magnet will eventually become disordered, and the positive and negative balance will weaken its sum field strength in space.
And you keep repeating the above process with different iron blocks, just accelerating the process.