The influence of 30 keV He$^+$ ion irradiation on structural, electronic and magnetic properties of Co$_2$MnSi thin films with B2 order was investigated. It was found, that irradiation with light ions can improve the local chemical order. This provok
es changes of the electronic structure and element-specific magnetization towards the bulk properties of the well-ordered Co$_2$MnSi Heusler compound with L2$_1$ structure.
We report on the influence of the improved L21 ordering degree on the magnetic properties of Co2MnSi Heusler films. Different fractions of the L21 phase are obtained by different post-growth annealing temperatures ranging from 350 degC to 500 degC. R
oom temperature magneto-optical Kerr effect measurements reveal an increase of the coercivity at an intermediate annealing temperature of 425 degC, which is a fingerprint of an increased number of pinning centers at this temperature. Furthermore, Brillouin light scattering studies show that the improvement of the L21 order in the Co2MnSi films is correlated with a decrease of the saturation magnetization by about 9%. The exchange stiffness constant of Co2MnSi, however, increases by about 8% when the L21 order is improved. Moreover, we observe a drop of the cubic anisotropy constant K1 by a factor of 10 for an increasing amount of the L21 phase.
