Magnetism of antiphase boundaries in ordered alloys studied using electron holography

Magnetic anomalies in antiphase boundaries (APBs), which are a type of planar defect produced in ordered crystals, have been studied using electron holography. For many ordered crystals, including a Ni₅₀Mn₂₅Al_12.5Ga_12.5 alloy with a Heusler-type structure, atomic disordering in the APB region (showing a finite thickness) deteriorates the ferromagnetic spin order. This relationship has several functions, such as the pinning of magnetic domain walls by APBs. However, in an Fe₇₀A1₃₀ alloy with a B2-type (CsCl-type) ordered structure, ferromagnetism can be developed by APBs. The unusual relationship observed in the Fe₇₀A1₃₀ alloy can provide useful information for engineering APB-induced phenomena. This paper reviews recent electron holography observations from these two types of alloys, and technical advancements in the APB studies.