Commensurate-incommensurate transition in helical magnetic structures

Abstract

The author has studied the commensurate-incommensurate transition for a system that exhibits helical magnetic structure. Such a transition occurs in the rare earth element Ho. The commensurability potential drives the system to a state where the period of the modulation is one half of the period of the lattice. It is shown that in the incommensurate state the angle, theta , between neighbouring spins can be expressed by an average angle and harmonic deviations around it. In the commensurate state, theta alternates between two values.