Magnetic correlations and Griffith-like phase in Co${}_2$TiSi${}_{0.5}$Al${}_{0.5}$ Heusler alloy

Abstract

We present a comprehensive study aimed at elucidating the complex magnetic correlations in Co${}_2$TiSi${}_{0.5}$Al${}_{0.5}$ Heusler alloy having the partial B2-type structure amid L2${}_1$ cubic main phase. The thermo-magnetization measurements at 100 Oe reveal the presence of two magnetic transitions at T${}_{C1}=278\mathrm{K}$ and T${}_{C2}=270\mathrm{K}$, respectively, with saturation magnetization of around 1.2 $\mu {}_{\mathrm{B}}$/f.u. at 5~K. Our magnetic field dependent studies reveal the dominance of T${}_{C1}$ transition at lower fields (${\mu }_0\mathrm{H}⩽0.03\mathrm{Tesla}$); however, at higher fields the T${}_{C2}$ transition becomes more pronounced. The observation of remnant magnetization above Curie temperature suggests the development of Griffiths-like phase, which is extensively analyzed through {\it ac} and {\it dc}- magnetic susceptibility ($\chi$) data. The evaluation of magnetocaloric potential indicates second order phase transition with notable $\Delta S_{\mathrm{M}}=$ 2.22 Jkg${}^{-1}$K${}^{-1}$ at 7 Tesla. The low-field (${\mu }_0\mathrm{H}⩽0.1\mathrm{Tesla}$) magnetic entropy ($\Delta S_{\mathrm{M}}$) curves exhibit two non-identical positive peaks. The nature and range of spin interactions near T${}_{\mathrm{C}}$ were scrutinized through rigorous critical phenomenon analysis, and the values of exponents $\alpha ,\beta ,\gamma$ and $\delta$ to be $0.063,0.361,1.108$ and $3.943$, respectively, which are found to be slightly deviating from mean-field theory towards 3D Heisenberg model. Additionally, the exchange magnetic interactions are found to decay as $J(r)\sim r^{-4.6}$. Furthermore, the density functional theory results reveal the half-metallic nature exhibiting 100\% spin polarization (SP). However, the electronic and magnetic properties are greatly affected by the incorporation of structural disorder, which results in drastic reduction of SP to mere 8.3\%.

submitted