Pinning of incommensurate spin-density waves by impurities

The pinning of incommensurate spin-density waves (SDW's) by both nonmagnetic and magnetic impurities is investigated in quasi-one-dimensional systems. Nonmagnetic impurities pin the SDW weakly by inducing a distortion of the total electron density near the impurity sites. Magnetic impurities have a stronger effect. Because of the local magnetic field produced by the SDW, the energy density has a periodicity equal to half the SDW wavelength. The dependence of the energy density on an external magnetic field is analyzed and predictions are made on the possibility of observing narrow-band noise in ``sliding'' SDW's.