Thanks to Frederik for his highlights,

by setting:
bfieldc
0.0 .0. 10.0
i get a total magnetic moment of: 

-0.2783699990E-19 0.1301609909E-19 -2.867197277 

but after setting
reducebf
0.75

tho total magnetic moment decrease every iteration until it became very small:
here bellow, the MOMENT.OUT file for SCF cycle:

-0.2783699990E-19 0.1301609909E-19 -2.867197277
0.1251810919E-18 0.3988457821E-19 -1.668360767
0.6191338539E-19 -0.5615394444E-20 -1.379373978
0.7347896801E-20 0.2443680691E-19 -1.084004127
-0.2580657003E-19 0.1607170329E-19 -0.9349549288
-0.4814645244E-19 0.2245462263E-19 -0.7872795972
-0.1366248740E-19 0.1656533472E-19 -0.6528726141
-0.9495394031E-20 0.5818447949E-20 -0.5312738989
0.1067300969E-19 -0.4366662723E-20 -0.4234078898

NB:
i used a large k-mesh:
ngridk
323232

and a more empty states:
nempty
10

So how can i maintain the total magnetic moment in this case?

many thanks