Magnetic field-induced strain in iron-based ferromagnetic shape memory alloys

Abstract

Magnetic field-induced strain (MFIS) along the [001]P (the symbol “P” represents parent phase) direction due to the conversion of martensite variants has been investigated for a disordered Fe–31.2Pd(at. %) single crystal and an ordered Fe3Pt single crystal exhibiting martensitic transformations from cubic phases to tetragonal phases at 85 and 230 K, respectively. The tetragonality c/a of Fe–31.2Pd at 77 K is 0.940 and that of Fe3Pt at 14 K is 0.945. When magnetic field is applied to the martensite phase along the [001]P direction, the specimen expands along the field direction for Fe–31.2Pd and contracts for Fe3Pt, suggesting that the c axis is the hard axis of magnetizaion for Fe–31.2Pd and is the easy axis for Fe3Pt. The conversion of variants by magnetic field is almost perfect for Fe–31.2Pd and is not perfect for Fe3Pt. The recoverable strain in the field removing process is small for Fe–31.2Pd and is about 0.6% for Fe3Pt. In the cooling process under magnetic field of 3.2 MA/m, the fraction of preferable variants reaches 100% in a narrow temperature range for Fe–31.2Pd, but it does not reach 100% for Fe3Pt (the maximum fraction is about 80%), although the fraction increases with decreasing temperature.

An Interpretation of Martensitic Transformation in L1<SUB>2</SUB>-Type Fe<SUB>3</SUB>Pt from Its Electronic Structure

“…5,6) It is now well understood that a large magnetocrystalline anisotropy energy and small twinning shear of the FCT martensite are important for realizing the rearrangement of martensite variants under a magnetic field. However, the origin of such second-order-like transformation and the resulting small twinning shear are not clarified yet.…”

Magnetic field guided formation of long carbon filaments (sausages)

“…Recently, magnetic field-induced growth and self-assembly of cobalt nanocrystallites was studied by Niu et al [5]. Other reports in which a chemical reaction was conducted in a magnetic field include the order observed in assemblies of superparamagnetic carrier particles reported by Rotariu [6], strain detected in iron-based ferromagnetic shape memory alloys reported by Sakamoto et al [7] and superconductivity measured in hybrid ferromagnets [8].…”

Magneto-Structural Properties of Ni2MnGa Ferromagnetic Shape Memory Alloy in Magnetic Fields

“…The martensite variants exhibit configurations typical of self-accommodation arrangements. The typical width of a variant is about 1 μm, by means of the TEM image of Ni 54 Mn 25 Ga 21 , which is shown in [7], and the strict twin structure of the microstructure is beneficial to the thermoelasticity of its martensitic transformation. A few studies discussed the interaction between magnetism and crystallographic rearrangements [1,8,9,17,18].…”

“…The strain is the result of field-induced twin boundary motion. A disordered Fe-31.2%Pd (at.%) alloy (A1-type cubic) [53,54], and an ordered Fe 3 Pt (L1 2 -type cubic) ferromagnetic alloy [55,56], have attracted considerable interest due to the large MFISs. The Ni-Mn-Ga, Fe-Pd, and Fe-Pt alloy shave attracted considerable attention as materials for magnetic actuators.…”