Antiferromagnetic exchange interactions among dopant electrons in Si nanowires

Magnetic interactions among substitutional dopant impurities in silicon nanowires are investigated theoretically using density functional calculations. Our results show that while dopant impurities in silicon nanowires have no magnetic ordering in the ground state, a magnetic moment imposed at an impurity by applying an effective local magnetic field induces a magnetic moment, smaller in magnitude and opposite in sign, at an adjacent impurity, demonstrating an antiferromagnetic coupling between the impurity spins. The sign of the calculated Heisenberg exchange parameter J between the impurity spins also corresponds to the antiferromagnetic coupling and its magnitude decreases monotonically as the distance between impurities increases. Our results suggest that, while there is no static magnetic moment on dopant impurity atoms, a direct exchange interaction between impurity states of the dopants may result in an instantaneous short-range antiferromagnetic correlation between the impurity spins, confirming the suggestion from a recent experimental work observing the Kondo-like temperature dependence of the electrical resistance of doped silicon nanowires.