Critical behavior near the ferromagnetic-paramagnetic transformation in the austenite phase of Ni₄₃Mn₄₆Sn₈X₃ (X=In and Cr) Heusler alloys

다국어 초록 (Multilingual Abstract)

<P><B>Abstract</B></P> <P>In this work, we present a detailed study on the magnetic property and critical behavior in the austenitic phase of Ni<SUB>43</SUB>Mn<SUB>46</SUB>Sn<SUB>8</SUB>X<SUB>3</SUB> alloys with X=Cr and In, which were prepared by an arc-melting method in an argon ambience. The <I>M</I>(<I>T</I>) curve of the Cr sample (X=Cr) exhibits a single magnetic phase transition at the Curie temperature of the ferromagnetic (FM) austenitic phase with <I>T</I> <SUP>A</SUP> <SUB>C</SUB> =303K. In contrast, the In sample (X=In) exhibits multiple magnetic phase transitions, including a magnetic phase transition from a FM state to weakly magnetic state at <I>T</I> <SUP>M</SUP> <SUB>C</SUB> =165K of the martensitic phase, a martensitic transition from the weakly magnetic to the FM austenite phase at <I>T</I> <SUP>M-A</SUP> =259K, and a magnetic phase transition from the FM to paramagnetic (PM) at <I>T</I> <SUP>A</SUP> <SUB>C</SUB> =297K of the austenite phase. Based on the Landau theory and <I>M</I>(<I>H</I>) data measured at different temperatures, we pointed that the FM-PM phase transitions around <I>T</I> <SUP>A</SUP> <SUB>C</SUB> in both samples were the second-order phase transition. Our results suggest an existence of the long-range FM interactions in the austenite phase. A small deviation from the mean-field theory of the critical exponents has been also observed pointing out an existence of the inhomogeneous magnetism that could be associated with the presence of the anti-FM interactions in these samples. Besides, their effective exponents <I>β</I> <SUB>eff</SUB>(<I>ε</I>) and <I>γ</I> <SUB>eff</SUB>(<I>ε</I>) have been also calculated.</P>