| Summary: | Heusler alloy with an atomic composition of Ni<sub>51.82</sub>Mn<sub>32.37</sub>In<sub>15.81</sub> was prepared by melt spinning from arc-melted ingots. X-ray diffraction, scanning electron microscopy and magnetic measurements were used to study the structural, microstructural and magnetic properties. The crystal structure consists of a mixture of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>B</mi><mn>2</mn></mrow></semantics></math></inline-formula> austenite (~50%) and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mn>14</mn><mi>M</mi></mrow></semantics></math></inline-formula> martensite (~50%). The alloy undergoes a second order magnetic transition at a Curie temperature of <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msubsup><mi>T</mi><mi>c</mi><mi>A</mi></msubsup><mo>=</mo><mn>194.2</mn><mtext> </mtext></mrow></semantics></math></inline-formula>K. The hysteresis loop reveals the occurrence of exchange bias phenomenon at room temperature. The critical exponents <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>β</mi></semantics></math></inline-formula>, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>γ</mi></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>δ</mi></semantics></math></inline-formula> were estimated using modified Arrott plots, Kouvel–Fisher curves and critical isothermal analysis. The respective values are <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>β</mi><mo>=</mo><mn>0.500</mn><mo>±</mo><mn>0.015</mn></mrow></semantics></math></inline-formula>, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>γ</mi><mo>=</mo><mn>1.282</mn><mo>±</mo><mn>0.055</mn></mrow></semantics></math></inline-formula> and <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mi>δ</mi><mo>=</mo><mn>3.003</mn><mo>±</mo><mn>0.002</mn></mrow></semantics></math></inline-formula>. The critical behaviour in ribbons is governed by the mean field model with a dominated long-range order of ferromagnetic interactions. The maximum entropy change, <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><mo>∆</mo><msubsup><mi>S</mi><mi>M</mi><mrow><mi>m</mi><mi>a</mi><mi>x</mi></mrow></msubsup></mrow></semantics></math></inline-formula>, for an applied magnetic field of 5 T reaches an absolute value of 0.92 J/kg·K. The experimental results of entropy changes are in good agreement with those calculated using Landau theory.
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