On the Magnetism of the Normal State in MgB2

The experimentally observed ferromagnetism in MgB2 in the normal state is attributed to microphase-separated inclusions of iron. This magnetic character is also observed when the iron content of the samples is reduced below 20 μg/g, however in these samples the diamagnetism of MgB2 is apparent and is measured. It is found experimentally that the diamagnetic susceptibility at room temperature of B element, MgB2, and MgB4 is close to the ratio 1:2:4, suggesting that the diamagnetism in these borides is confined to the boron atoms. This observation supports a picture in which the two electrons of Mg are donated to B in MgB2.