Magnetic properties of exchange-coupled α-Fe/Nd–Fe–B multilayer thin-film magnets

The multilayer thin films having the form of Ti(30 nm)/Fe(dFe)/[Nd–Fe–B(dNd–Fe–B)/Fe(dFe)] ×5/Ti(30 nm)/glass were fabricated on glass substrates by means of radio frequency (rf) sputtering, with dFe varied from 0 to 50 nm and dNd–Fe–B from 0 to 100 nm. Magnetization measurements have revealed that the minor loops of the films are reversible in a certain range of demagnetization fields except for the films with dFe∼0 nm or dNd–Fe–B<10 nm. Micromagnetic calculation of magnetization curves has been performed, which has well reproduced the observed hysteresis loops including spring-back behavior and the dependence of the coercive field HcJ on dFe and dNd–Fe–B. From the comparison between experiment and calculation, we can infer that the interlayer exchange-coupling strength is about 10% of the intralayer couplings, which are found to be almost independent of dFe and dNd–Fe–B.