Anomalous shift of magnetic resonance line in disordered and noncollinear magnetics

It is established that anomalous shift of magnetic resonance line in spin glasses is a general feature of noncollinear magnetics, and it is observed in helical antiferromagnetics too. The shift appears with appearing of a noncollinear magnetic short-range order. A nonuniform spin precession is excited in noncollinear magnetics. An effective exchange field acts on a spin under nonuniform precession. Using hydrodynamic theory of spin waves in spin glasses, it is shown that the value of the shift may be of the order of the resonance field, if a certain parameter, characterizing the degree of noncollinearity of the spin structure, is of the order of unity