Abstract
In this work, we investigated the phase transition and electronic structures of some newly designed all-d-metal Heusler compounds, X2MnTi (X = Pd, Pt, Ag, Au, Cu, and Ni), by means of the first principles. The competition between the XA and L21 structures of these materials was studied, and we found that X2MnTi favors to feature the L21-type structure, which is consistent with the well-known site-preference rule (SPR). Under the L21 structure, we have studied the most stable magnetic state of these materials, and we found that the ferromagnetic state is the most stable due to its lower energy. Through tetragonal deformation, we found that the L21 structure is no longer the most stable structure, and a more stable tetragonal L10 structure appeared. That is, under the tetragonal strain, the material enjoys a tetragonal phase transformation (i.e., from cubic L21 to tetragonal L10 structure). This mechanism of L21-L10 structure transition is discussed in detail based on the calculated density of states. Moreover, we found that the energy difference between the most stable phases of L10 and L21, defined as ΔEM (ΔEM = ECubic-ETetragonal), can be adjusted by the uniform strain. Finally, the phonon spectra of all tetragonal X2MnTi (X = Pd, Pt, Ag, Au, Cu, and Ni) phases are exhibited, which provides a powerful evidence for the stability of the tetragonal L10 state. We hope that our research can provide a theoretical guidance for future experimental investigations.
Highlights
Magnetic shape memory compounds (MSMAs) (O’Handley, 1998) are a new type of intelligent materials which integrates magnetic controlled shape memory and magnetic field-induced strain simultaneously
Based on the above information, we focus on the electronic structures and phase transition of all-d-metal Heusler compounds X2MnTi (X = Pd, Pt, Ag, Au, Cu, and Ni) with the help of the first principles
We investigated the phase transition and electronic structures of X2MnTi (X = Pd, Pt, Ag, Au, Cu, and Ni) compounds based on first-principle calculations
Summary
Magnetic shape memory compounds (MSMAs) (O’Handley, 1998) are a new type of intelligent materials which integrates magnetic controlled shape memory and magnetic field-induced strain simultaneously. It can be used as key components of sensors and brakes in the future. MSMAs have both thermoplastic martensitic transformation (Oikawa et al, 2001) and magnetic transformation (Oikawa et al, 2002), and their shape memory effect can be controlled by the magnetic field. MSMAs enjoy magnetoresistance (Ullakko et al, 1996) and magnetocaloric (GschneidnerJr et al, 2005) effects, so they have been regarded as a research hot spot in recent years. Heusler (Graf et al, 2011; Birkel et al, 2013; Ahmadian and Salary, 2014; Kirievsky et al, 2014; Xue et al, 2016; Miranda and Gruhn, 2017; Ghunaim et al, 2018; Li et al, 2019, 2020) compounds
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