Study of antiferromagnetic and nematic phase transitions in $BaF{e}_2(A{s}_{1-x}{P}_x{)}_2$ by AC micro-calorimetry and SQUID magnetometry

Abstract

We study the antiferromagnetic (AFM) and structural phase transitions in single crystal $BaF{e}_2(A{s}_{1-x}{P}_x{)}_2$ $(x=0,0.3)$ at temperatures $T_N$ and $T_S$, respectively, by high resolution ac microcalorimetry and SQUID magnetometry. The specific heat measurements of both as grown and annealed $BaF{e}_{2}A{s}_2$ displays a sharp peak at the AFM/Structural transitions. A kink in the entropy of annealed $BaF{e}_{2}A{s}_2$ gives evidence for splitting of the two transitions by approximately 0.5K. No additional features could be identified in the specific heat of both $BaF{e}_{2}A{s}_2$ and $BaF{e}_2(A{s}_{0.7}{P}_{0.3}{)}_2$ in the temperature regions around $T^{\ast }$ > $T_S$ where torque measurements [S. Kasahara et al., Nature 486, 382 (2012)] had revealed the "true" nematic phase transition, indicating that the behavior at $T^{\ast }$ does not represent a 2nd order phase transition, and that the phase transition of $BaF{e}_2(A{s}_{1-x}{P}_x{)}_2$ into the orthorhombic phase does occur at $T_S$.

22 pages including 5 figures

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