Hard magnetic properties of NdFeB/Co films annealed in the presence of a magnetic field

The influence of an anneal in the presence of a magnetic field on the magnetic properties of sputtered Nd₂Fe₁₄B/Co films is reported. As the Co content increases from 0 to 22 weight % the remanent magnetization increases from 0.68 to 0.95 T, the coercivity decreases from 2.3 to 0.55 T and the largest energy product, 85 kJ/m³, is obtained for the sample containing no Co. In the presence of an anneal field of 0.17 T an increase in the coercivity and energy product occur for intermediate Co concentration (14 weight %) and we obtain an energy product of 102kJ/m³. δM plots and the value of the spin reorientation temperature indicate that the exchange between the Nd₂Fe₁₄B and Co phases is larger for films annealed in an applied field and this correlates with the large energy products we measure in these films.