Magnetic Shape Memory Alloys (MSMAs) combine shape-change/deformationrecovery abilities of heat driven conventional shape memory alloys (SMA) and magnetic field driven magnetostrictives through martensitic transformation. They are promising for actuator applications, and can be employed as sensors/power-harvesters due to their capability to convert mechanical stimuli into magnetic response or vice versa. The purpose of the present work was to investigate magneto-thermo-mechanical (MTM) response of various MSMAs, under simultaneously applied magnetic field, heat and stress. To accomplish this, two novel testing systems which allowed absolute control on magnetic field and stress/strain in a wide and stable range of temperature were designed and manufactured. MTM characterization of MSMAs enabled us to determine the effects of main parameters on reversible magnetic field-induced phase transformation (FIPT), such as magnetocrystalline anisotropy energy, Zeeman energy, stress hysteresis, thermal hysteresis, critical stress to start stress induced phase transformation and crystal orientation. Conventional SMA characteristics of single crystalline Ni2MnGa and NiMnCoIn and polycrystalline NiMnCoAl and NiMnCoSn MSMAs were investigated using the macroscopic MTM testing system to reveal how these conventional properties were linked to magnetic-field-induced actuation. An actuation stress of 5 MPa and a work output of 157 kJm?3 were obtained by the field-induced martensite variant reorientation (VR) in NiMnGa alloys. FIPT was investigated both in Ni2MnGa MSMA and in NiMnCoIn metamagnetic SMA. It proved as an alternative governing mechanism of field-induced shape change to VR in Ni2MnGa single crystals: one-way and reversible (0.5% cyclic magnetic field induced strain (MFIS) under 22 MPa) stress-assisted FIPTs were realized under low field magnitudes (< 0.7 Tesla) resulting in at least an order of magnitude higher actuation stress levels than those in shape memory alloys literature. The possibility of harvesting waste mechanical work as electrical power by means of VR in NiMnGa MSMAs was explored: without enhanced pickup coil parameters or optimized power conditioning circuitry, 280 mV was harvested at 10 Hz frequency within a strain range of 4.9%. For the first time in magnetic shape memory alloys literature, a fully recoverable MFIS of 3% under 125 MPa was attained on single crystalline metamagnetic SMA NiMnCoIn by means of our microscopic MTM testing system to understand the evolution of FIPT under simultaneously applied magnetic field and stress. Conventional SMA characteristics of polycrystalline bulk NiMnCoAl and sintered compacted-powder NiMnCoSn metamagnetic SMAs were also investigated, with and without applied field.

In this study, the shape memory response of Ni2MnGa and NiMnCoIn magnetic shape memory alloys was observed under compressive stresses. Ni2MnGa is a magnetic shape memory alloy (MSMA) that has been shown to exhibit fully reversible, stressassisted magnetic field induced phase transformation (MFIPT) in the I X-phase transformation because of a large magnetostress of 7 MPa and small stress hysteresis. The X-phase is a recently discovered phase that is mechanically induced, however, the crystal structure is unknown. To better understand the transformation behavior of Ni2MnGa single crystal with [100] orientation, thermal cycling and pseudoelasticity tests were conducted with the goal of determining the Clausius-Clapeyron relationships for the various phase transformations. This information was then used to construct a stresstemperature phase diagram that illustrates the stress and temperature ranges where MFIPT is possible, as well as where the X-phase may be found. NiMnCoIn is a recently discovered meta-magnetic shape memory alloy (MMSMA) that exhibits unique magnetic properties. The ferromagnetic parent phase and the paramagnetic martensite phase allow the exploitation of the Zeeman energy. To gain a better understanding of the transformation behavior of NiMnCoIn, thermal cycling and pseudoelasticity tests were conducted on single crystals from two different batches with crystallographic orientations along the [100](011), [087], and [25 7 15] directions. A stress-temperature phase diagram was created that illustrates the Clausius- Clapeyron relationships for each orientation and batch. SQUID tests revealed the magnetic response of the alloy as well as the suppression of the martensite start temperature with increasing magnetic field. Pseudoelasticity experiments with and without magnetic field were conducted to experimentally quantify the magnetostress as a function of magnetic field. For the first time, it has been shown that NiMnCoIn is capable of exhibiting magnetostress levels of 18-36 MPa depending upon orientation, as well as nearly 6.5% transformation strain in the [100] direction. The results of this study reveal increased actuation stress levels in NiMnCoIn, which is the main limitation in most MSMAs. With this increased blocking stress, NiMnCoIn is a strong candidate for MFIPT.