Pressure Induced Critical Behavior of Ferromagnetic Phase Transition in Sm-Nd-Sr Manganites

We report on the hydrostatic pressure dependence of the order of ferromagnetic (FM) to paramagnetic (PM) phase transition in a $({\mathrm{Sm}}_{0.7}{\mathrm{Nd}}_{0.3}{)}_{0.52}{\mathrm{Sr}}_{0.48}{\mathrm{MnO}}_3$ single crystal. At ambient pressure, the system undergoes a first-order FM-PM phase transition at 146 K. The application of pressure increases the $T_C$, suppresses the hysteresis width, and thus makes the transition second order. We have analyzed the critical behavior associated with the second-order FM-PM transition in the presence of an external pressure (12.1 kbar) and obtained the critical exponents $\beta =0.358$, $\gamma =1.297$, and $\delta =4.536$, which are close to those predicted for the three-dimensional Heisenberg system. Using these values of $\beta$, $\gamma$, and $T_C$ ($\sim 176\mathrm{K}$), one can scale the magnetization data below and above $T_C$ following a single equation of state.

Figure 1

(a) Magnetization ($M$) of $({\mathrm{Sm}}_{0.7}{\mathrm{Nd}}_{0.3}{)}_{0.52}{\mathrm{Sr}}_{0.48}{\mathrm{MnO}}_3$ single crystal as a function of magnetic field ($H$) between 131 K (top) and 170 K (bottom) in 3 K interval (data with increasing field are shown). Inset shows the hysteresis in $M(H)$ at $T=155\mathrm{K}$. (b) $M^2$ vs $H/M$ plot of the above isotherms. Insets show the $H$ dependence of differential susceptibility ($dM/dH$) for $140\mathrm{K}\le T\le 164\mathrm{K}$ in 6 K interval and $H\mathrm{\text{−}}T$ phase diagram.

Figure 2

Temperature dependence of magnetization ($M$) of $({\mathrm{Sm}}_{0.7}{\mathrm{Nd}}_{0.3}{)}_{0.52}{\mathrm{Sr}}_{0.48}{\mathrm{MnO}}_3$ single crystal for different pressures ($P$). Inset shows the $P$ dependence of $T_C$ and the thermal hysteresis width ($\Delta T$).

Figure 3

(a) $M$ vs $H$ of $({\mathrm{Sm}}_{0.7}{\mathrm{Nd}}_{0.3}{)}_{0.52}{\mathrm{Sr}}_{0.48}{\mathrm{MnO}}_3$ single crystal at $P=12.1\mathrm{kbar}$ between 162 K (top) and 188 K (bottom) in 2 K interval. Inset shows the $H$ dependence of ($dM/dH$) for $164\mathrm{K}\le T\le 188\mathrm{K}$ in 6 K interval. (b) $M^2$ vs $H/M$ plot of the above isotherms.

Figure 4

(a) Temperature dependence of spontaneous magnetization ($M_S$) and inverse initial susceptibility (${\chi }_0^{-1}$) of $({\mathrm{Sm}}_{0.7}{\mathrm{Nd}}_{0.3}{)}_{0.52}{\mathrm{Sr}}_{0.48}{\mathrm{MnO}}_3$ at $P=12.1\mathrm{kbar}$. (b) Kouvel-Fisher plots of $M_S$ and ${\chi }_0^{-1}$. (c) Scaling plots on a log-log scale, indicating two universal curves below and above $T_C$. Inset shows log-log plot of $M$ vs $H$ at $T=T_C$.