Large Magnetocaloric Effect and Magnetoresistance in Fe and Co Co‐Doped Ni‐Mn‐Al Heusler Alloys

Abstract

The Ni 40 Co 10Àx Fe x Mn 33 Al 17 (x ¼ 4, 6, 8) alloys are prepared by arc-melting method. The crystallographic structure, magnetic and magnetoresistance properties are systematically studied. The large magnetic change is obtained across the martensitic transformation from the ferromagnetic austenite phase to weak-magnetic martensite phase. With the increase in Fe/Co ratio, the martensite transformation temperature shifts to the lower temperature. The large values of magnetoresistance of 33.3, 25.7, and 13.1% are achieved at the field of 3 T for x ¼ 4, x ¼ 6, and x ¼ 8 alloys around the martensitic transformation, respectively. These results indicate that Ni-Fe-Co-Mn-Al alloy provides the motive power for further research in practical applications.

Magnetocaloric and Elastocaloric Effects in All‐d‐Metal Ni37Co9Fe4Mn35Ti15 Magnetic Shape Memory Alloy

“…The relationship between Δ S m pk and the magnetic field is almost linear. The similar near‐linear relationship is also observed in Ni 40 Co 10− x Mn 33 Al 17 alloys and Ni 1.7 Co 0.3 Mn 1+ x Al 1− x alloys …”

“…In the heating process, the magnetization maintains its initial value at the beginning and then a sudden jump of magnetization is observed between the austenite start temperature ( A s ), 276 K, and austenite finish temperature ( A f ), 303 K, corresponding to the transition associated with reverse MT. On further heating, the austenite phase shows a magnetic transition from FM state to paramagnetic state near the Curie temperature ( T c ) of 305 K. The T c is determined by the peak temperature of the dM/dT versus T curve, as shown in the inset of Figure a . Moreover, a thermal hysteresis of magnetization transition between cooling and heating during forward and reverse MT can be observed, which is a signature of the first‐order transition.…”

“…However, Co substituted by Fe will weaken the FM exchange interaction in some Heusler alloys due to the relatively weak interactions between Mn and Fe . At the same time, the substitution Co with Fe plays a critical role in tuning MT temperature due to the change in the number of valence electrons …”

“…Among those bondings, the Mn–Co interaction in austenite is stronger than that of other interactions . Thus, the local Mn–Co–Mn configuration is built, which have been proved to exhibits FM coupling with parallel magnetic moments . The Fe‐doping in some Heusler alloys could also modify the magnetic structure of the austenite phase with FM being the preferred state .…”

“…Liu et al reported a relative high MT temperature in NiMnTi(Co), which would adversely affect RT refrigeration . In our previous study, it was proved that the substitution Co with Fe would significantly reduce the MT temperature . More importantly, it was reported that Fe‐doping could significantly improve the mechanical properties and also contribute to achieving the enhanced eC performance in Ni‐Fe‐Mn‐Al alloys .…”