Calorimetric study of aligned liquid crystal + aerosil

A high-resolution ac-calorimetric study was performed on magnetically aligned colloidal dispersions of 8CB and aerosil spanning the weakly first-order \textit{I}-\textit{N} and second order \textit{N}-Sm\textit{A} phase transitions. Stable aligned samples were prepared by repeated cycling between the isotropic and nematic phase in the presence of a $2$~T magnetic field. Zero-field measurements were carried out on six aligned conjugate density samples ranging from $0.03$ to $0.15$~g~cm$^{-3}$ (mass of aerosil per volume of liquid crystal). For comparison, two unaligned samples from the same batch ($0.05$ and $0.13$~g~cm$^{-3}$) were also studied. The unaligned samples reproduce very closely previous studies on this system. The magnetically aligned samples, exhibits lower transition temperatures for the same aerosil density sample and a shift to higher aerosil density of the non-monotonic $T_c$ evolution. The clear differences between aligned and unaligned sample indicate the ``memory'' of the magnetic field even after heating deep into the isotropic phase. The origin of this ``memory'' remains unexplained.