Field-induced first-order to second-order magnetic phase transition in ${\text{Sm}}_{0.52}{\text{Sr}}_{0.48}{\text{MnO}}_3$

We report on the magnetic field $\left(H\right)$ dependence of the order of the ferromagnetic (FM) to paramagnetic (PM) phase transition in ${\text{Sm}}_{0.52}{\text{Sr}}_{0.48}{\text{MnO}}_3$ single crystal. For $H<4\text{T}$, magnetization and specific-heat data show a first-order phase transition, with sharp drop of magnetization along with hysteresis, and large, symmetric, and narrow specific-heat peak with finite amount of entropy change at $T_C$. By contrast, for $H\ge 4\text{T}$, the phase transition becomes essentially second-order with tricritical point exponents $\beta \sim 0.32$ and $\gamma \sim 1.31$. The tricritical point separates first-order $\left(H<4\text{T}\right)$ from second-order $\left(H\ge 4\text{T}\right)$ transition.

Figure 1

(a) Isothermal magnetization ($M$ vs $H$) of ${\text{Sm}}_{0.52}{\text{Sr}}_{0.48}{\text{MnO}}_3$ single crystal (data with increasing field are shown). (b) Hysteresis in $M\left(H\right)$ at 110 and 170 K. (c) Magnetization isotherms replotted as $H/M$ vs $M^2$ between 110 K (bottom) and 120 K (top) in 2 K interval.

Figure 2

(a) Temperature dependence of magnetization (heating cycle) for ${\text{Sm}}_{0.52}{\text{Sr}}_{0.48}{\text{MnO}}_3$ single crystal at different magnetic fields. (b) $H$ dependence of ${\Delta }_M$. Inset shows thermal hysteresis of $M$ at $H=2\text{kOe}$. (c) $T_C-H$ phase diagram. Closed and open symbols are transition temperatures derived from the heating and cooling cycles of $M\left(T\right)$ curves, respectively. (d) Modified Arrott plots [$M^{1/\beta }$ vs ${\left(H/M\right)}^{1/\gamma }$] in the high field $H\ge 9\text{T}$ and high temperature $188\text{K}\le T\le 203\text{K}$ (with 3 K interval) regime with $\beta =0.32$ and $\gamma =1.31$.

Figure 3

(a) Molar specific heat (after subtracting the background), $C_{\text{mag}}$ vs temperature. Inset: $T$ dependence of specific heat $\left(C_p\right)$ of ${\text{Sm}}_{0.52}{\text{Sr}}_{0.48}{\text{MnO}}_3$ single crystal for different $H$. (b) Thermal distribution of $T\left(dQ/dT\right)$ for different fields. Inset: $T$ dependence of thermoelectric power $\left(Q\right)$ of ${\text{Sm}}_{0.52}{\text{Sr}}_{0.48}{\text{MnO}}_3$ single crystal.

Figure 4

Magnetic entropy $S_{\text{mag}}$ calculated by integrating $C_{\text{mag}}/T$ around $T_C$ for $H=0$ and 5T. Inset: magnetic-field dependence of $\Delta S_{\text{mag}}$ (closed square) and ${\Delta }_C$ (open circle).