Superposition of conventional and spontaneous exchange bias in a Ni₅₀Mn₃₄In₁₃Fe₃ magnetic shape memory alloy

The conventional exchange bias and spontaneous exchange bias are two interesting but fundamentally different effects in Mn rich Ni-Mn-Z magnetic shape memory alloys. Previous investigations show that these two phenomena appear separately. Here, we report that the conventional and spontaneous exchange bias phenomena coexist in a Ni₅₀Mn₃₄In₁₃Fe₃ alloy and the superposition of them increases the total exchange bias of the alloy. Our results suggest that the canonical spin glass and super spin glass may coexist and are embedded in the antiferromagnetic matrix of the martensite, through properly tuning the temperature-field history, which further results in the superposition of conventional and spontaneous exchange bias for this alloy. The interfacial interaction between the canonical spin glass and the antiferromagnetic matrix forms during field cooling process, which results in the conventional exchange bias. Moreover, the application of large magnetic field during the isothermal magnetization process changes the superspin glass into a superferromagnetic state, which interacts with the antiferromagnetic matrix at the interface, causing the spontaneous exchange bias. The superposition of exchange bias provides an effective way to achieve large exchange bias in materials.