Experimental probing of exchange interactions between localized spins in the dilute magneticinsulator (Ga,Mn)N

The sign, magnitude, and range of the exchange couplings between pairs of Mn ions is determined for(Ga,Mn)N and (Ga,Mn)N:Si with x 3%. The samples have been grown by metalorganic vapor phase epitaxyand characterized by secondary-ion mass spectroscopy; high-resolution transmission electron microscopy withcapabilities allowing for chemical analysis, including the annular dark-field mode and electron energy lossspectroscopy; high-resolution and synchrotron x-ray diffraction; synchrotron extended x-ray absorption finestructure;synchrotron x-ray absorption near-edge structure; infrared optics; and electron spin resonance. Theresults of high-resolution magnetic measurements and their quantitative interpretation have allowed us to verify aseries of ab initio predictions on the possibility of ferromagnetism in dilute magnetic insulators and to demonstratethat the interaction changes from ferromagnetic to antiferromagnetic when the charge state of the Mn ions isreduced from 3+ to 2+.