The impact of B substitution in Ni₅₀Mn₃₅In_15−xB_x Heusler alloys on the structural, magnetic, transport, and parameters of the magnetocaloric effect (MCE) has been studied by means of room-temperature X-ray diffraction and thermomagnetic measurements (in magnetic fields (H) up to 5 T, and in the temperature interval 5–400 K). Direct adiabatic temperature change (ΔT_AD) measurements have been carried out for an applied magnetic field change of 1.8 T. The transition temperatures (T-x) phase diagram has been constructed for H = 0.005 T. The MCE parameters were found to be comparable to those observed in other MCE materials such as Ni₅₀Mn_34.8In_14.2B and Ni₅₀Mn₃₅In₁₄X (X=In, Al, and Ge) Heusler alloys. The maximum absolute value of ΔT_AD = 2.5 K was observed at the magnetostructural transition for Ni₅₀Mn₃₅In_14.5B_0.5.

Magnetization, electrical resistivity, magnetoresistance, and Hall resistivity of $\mathrm{N}{\mathrm{i}}_{50}\mathrm{M}{\mathrm{n}}_{35}\mathrm{I}{\mathrm{n}}_{14.25}{\mathrm{B}}_{0.75}$ and $\mathrm{N}{\mathrm{i}}_{50}\mathrm{M}{\mathrm{n}}_{35}\mathrm{I}{\mathrm{n}}_{14.5}{\mathrm{B}}_{0.5}$ Heusler alloys were studied in a temperature range $T=80–400\mathrm{K}$ in magnetic fields up to 20 kOe. Both alloys exhibit a martensitic transformation from a high-temperature ferromagnetic austenite phase to a low-temperature, low-magnetization martensitic phase. The electrical resistivity nearly doubles as a result of the martensitic transformation, reaching 180 and 100 µΩ cm in the martensitic states of $\mathrm{N}{\mathrm{i}}_{50}\mathrm{M}{\mathrm{n}}_{35}\mathrm{I}{\mathrm{n}}_{14.25}{\mathrm{B}}_{0.75}$ and $\mathrm{N}{\mathrm{i}}_{50}\mathrm{M}{\mathrm{n}}_{35}\mathrm{I}{\mathrm{n}}_{14.5}{\mathrm{B}}_{0.5}$, respectively. The temperature dependence of the electrical resistivity does not corresponded with the Mooij correlation. The magnetoresistance is negative with a narrow negative peak at the martensitic transition. Normal and anomalous Hall effect coefficients were determined by fitting the field dependences of the Hall resistivity using magnetization data. The coefficients of the normal Hall effect for both compositions were found to decrease with temperature from positive values in the austenite to negative values in the martensite phase. None of the known correlations between the anomalous Hall effect coefficient and resistivity were satisfied. Significant changes in the values of the anomalous Hall coefficients during the martensitic transformation are explained by the difference in spin-up and spin-down state occupations in the martensite and austenite phases. First-principles calculations of the electronic structures confirm this explanation.