First principles theory of spin waves in Fe, Co, and Ni

Using constrained local spin density functional theory it is possible to di rectly calculate the adiabatic magnon dispersion curve. Small amplitude mag nons with wavelengths between 2 and 32 atomic layers were constructed and t he energy change with respect to amplitude within the frozen potential appr oximation was calculated. The resulting dispersion curves give the spin wav e stiffness for [111] face-centered-cubic Co and Ni in fair agreement with experiment. In Fe the stiffness was calculated along [100] and [110] direct ions. The two values of stiffness were found to be nearly equal to each oth er and roughly half the measured value. It was found that the calculated Fe stiffness did not change upon addition of gradient corrections to the loca l density approximation, indicating that the source of discrepancy is not l ikely a failure of the local density approximation. It is argued that the a diabatic approximation is more likely the source of discrepancy since the m agnetic interactions in Fe are longer ranged than those in Co or Ni, thus m aking the dynamical retardation effect more important in Fe. (C) 1999 Ameri can Institute of Physics. [S0021-8979(99)58708-2].