Detection of the ferromagnetic properties of Si:P in the region of an insulator–metal phase transition

The ferromagnetic properties of Si:P in the region of a concentration insulator–metal phase transition at liquid helium temperatures have been detected and studied. To determine the spin component of the magnetization, the diamagnetic contribution linear in field has been subtracted from the total magnetizations of samples measured by a SQUID magnetometer. The spin magnetization has strong nonlinearity with saturation in fields of about several oersteds and a hysteresis loop, which are characteristic of ferromagnets. The capability of magnetization decreases sharply with the shift away from the phase transition point on the insulator side of the phase transition. However, it increases strongly at a nearly half degree of compensation of Si:P by acceptor impurities. The results indicate that the triplet state for some pairs of exchange-coupled spins (ferromagnetic phase) in Si:P in the region of the insulator–metal phase transition at low temperatures is more energy favorable than the singlet state (antiferromagnetic phase) largely because of a moderate compensation.