Abstract
Epitaxial {111} Ni 0.82 Fe 0.18 O films (NiFeO) were prepared by using solid-source metal-organic chemical vapor deposition on {0001} α-Al 2 O 3 . The exchange anisotropy between NiFeO and Ni 80 Fe 20 (NiFe) was investigated. Structural and chemical analyses showed that NiFeO films were compositionally homogeneous. The 60-degree rotational twins formed in the NiFeO films. The epitaxial relationship between Ni 0.82 Fe 0.18 O and Al 2 O 3 is the following: [111] NiFeO||[0001]α-Al 2 O 3 , [110]NiFeO||[1100]α-Al 2 O 3 , and [112]NiFeO||[1120]α-Al 2 O 3 . The orientation relationship between NiFeO and NiFe is cube-to-cube. Misfit dislocations pile up at the interfaces significantly reduce the stress, and result in semi-coherent interfaces. In-plane tension and out-of-plane compression were developed in NiFeO films due to the thermal stress, which may force the magnetic moment of NiFeO to lie in the {111} planes parallel to the film surface, and may lead to a strong interfacial coupling between NiFeO and NiFe. The relative small exchange field possibly results from (1) a low anisotropy energy compared to the interfacial coupling energy in the NiFeO {111} plane, (2) an orientation distribution of the easy axes in the NiFeO {111} plane, and (3) the large domain size of NiFeO. The Malozemoff model was used to estimate the exchange field in this system. Based on the assumption that the domain size of the NiFeO is approximately equal to the twin size, the calculated exchange field agrees well with the experimental results. © 2001 American Institute of Physics.