Magnetic Field‐Induced Phase Transformation in NiMnCoIn Magnetic Shape‐Memory Alloys—A New Actuation Mechanism with Large Work Output

TLDR

Magnetic shape memory alloys enable magnetic‑field‑induced actuation and related functions, but require relatively high critical fields (1.5–3 T) for reversible phase transformation. The study characterizes the magnetic‑field‑induced martensitic phase transformation in Ni₄₅Mn₃₆.₅Co₅In₁₃.₅ single crystals as a new actuation mechanism capable of ultra‑high work output. The authors examine how magnetic fields affect transformation temperatures, magnetization, and superelasticity, quantify orientation‑dependent strains and magnetostress, and develop a thermodynamic model of the phase transformation. NiMnCoIn alloys achieve over 1 MJ m⁻³ T⁻¹ of magnetic work output—an order of magnitude higher than NiMnGa—independent of orientation, with [111] crystals reaching 140 MPa T⁻¹ and 1.2 % strain, surpassing existing actuators and enabling high‑frequency, high‑work‑output applications.

Abstract

Abstract Magnetic shape memory alloys (MSMAs) have recently been developed into a new class of functional materials that are capable of magnetic‐field‐induced actuation, mechanical sensing, magnetic refrigeration, and energy harvesting. In the present work, the magnetic &!hyphen;field‐induced martensitic phase transformation (FIPT) in Ni 45 Mn 36.5 Co 5 In 13.5 MSMA single crystals is characterized as a new actuation mechanism with potential to result in ultra‐high actuation work outputs. The effects of the applied magnetic field on the transformation temperatures, magnetization, and superelastic response are investigated. The magnetic work output of NiMnCoIn alloys is determined to be more than 1 MJ m −3 per Tesla, which is one order of magnitude higher than that of the most well‐known MSMAs, i.e., NiMnGa alloys. In addition, the work output of NiMnCoIn alloys is orientation independent, potentially surpassing the need for single crystals, and not limited by a saturation magnetic field, as opposed to NiMnGa MSMAs. Experimental and theoretical transformation strains and magnetostress levels are determined as a function of crystal orientation. It is found that [111]‐oriented crystals can demonstrate a magnetostress level of 140 MPa T −1 with 1.2% axial strain under compression. These field‐induced stress and strain levels are significantly higher than those from existing piezoelectric and magnetostrictive actuators. A thermodynamical framework is introduced to comprehend the magnetic energy contributions during FIPT. The present work reveals that the magnetic FIPT mechanism is promising for magnetic actuation applications and provides new opportunities for applications requiring high actuation work‐outputs with relatively large actuation frequencies. One potential issue is the requirement for relatively high critical magnetic fields and field intervals (1.5–3 T) for the onset of FIPT and for reversible FIPT, respectively.