Evaluation of Exchange Coupling in α-Fe(100)/Nd₂Fe₁₄B(001) Interface

Abstract

  Magnetic bilayer films with an interface of α-Fe(100) and Nd₂Fe₁₄B(001) planes were fabricated in order to evaluate the exchange-coupling constant, which was recently reported to depend on the Miller indices of the interface planes. The epitaxial growth of both α-Fe and Nd₂Fe₁₄B layers was confirmed with the epitaxial relation of MgO(100)[100] || α-Fe(100)[110] || Nd₂Fe₁₄B(001) [110], according to the X-ray pole-figure measurements. FMR experiments on this film were performed by using a Q-band microwave apparatus. We observed a significant shift of α-Fe resonance field from H_r = 5.24 kOe to H_r = 4.41 kOe in a bilayer film sputtered at T_S^NFB = 650°C compared to a reference film without an Nd₂Fe₁₄B layer. This lower shift suggests the existence of an internal field due to the positive exchange coupling between α-Fe and Nd₂Fe₁₄B phases. The magnitude of the exchange-coupling constant was estimated to be in the range between 6.5 and 11 erg/cm² for the bilayer film sputtered at T_S^NFB = 650°C.