A novel physical phenomenon has been observed that resembles a large asymmetric switchinglike magnetoresistance at low applied fields in bulk metamagnetic Heusler alloys. A thermally activated isothermal forward metamagnetic transition with a signature of a pronounced time-dependent relaxation was observed in a bulk B-substituted off-stoichiometric Ni-Mn-In Heusler alloy, whereas the reverse metamagnetic transition exhibited the usual athermal behavior with no thermal activation. The asymmetry between the forward and reverse metamagnetic transitions resulted in a large switchinglike, low-field magnetoresistance (∼16% for a field change of $B$ = 0 → 0.25 T at $T$ = 304 K) in the bulk Heusler alloys, ${\mathrm{Ni}}_{50}{\mathrm{Mn}}_{35}{\mathrm{In}}_{15-x}{\mathrm{B}}_x$ (1 ⩽ $x$ ⩽ 2).

• Received 21 May 2014
• Revised 25 July 2014

DOI:https://doi.org/10.1103/PhysRevB.90.064412