Disorder effects in Ising metamagnetic phase transition

Abstract

The thermodynamics of randomly quenched disordered Ising metamagnet has been studied by Monte Carlo simulations. The disorder has been implemented either by inserting nonmagnetic impurity or by uniformly distributed quenched random magnetic field. The staggered magnetisation ($M_s$) (calculated from the sublattice magnetisation) and the corresponding staggered susceptibility ($χ$) are studied as functions of the temperature ($T$). The antiferromagnetic phase transition has been found while cooling the system from the high temperature paramagnetic phase. The transition temperature(or pseudocritical temperature ($T_c$)) has been found to decrease as the concentration ($p$) of nonmagnetic impurity increased. The nonmagnetic impurity dependent staggered magnetisation has been found to show the scaling behaviour $M_sp^b \sim (T-T_c)p^a$ (with $a \cong -0.95$, $b \cong 0.09$ and $T_c \cong 4.45$) obtained through the data collapse. The zero temperature staggered magnetisation ($M_s(0)$) has been found to decrease linearly. The critical temperature($T_c$) is showing a linear ($T_c=mp+c$) dependence with the concentration ($p$) of nonmagnetic impurity. The antiferromagnetic phase transition has been found to take place at lower temperature for the higher value of the width ($s$) of the uniformly distributed quenched random field. The critical temperature ($T_c$) has been found to show the nonlinear dependence ($T_c=a+bs+cs^2$) on the width ($s$) of the uniformly distributed random magnetic field. The extrapolation (both for $p \to 0$ and $s \to 0$) restores the Neel temperature of three dimensional pure Ising antiferromagnet.

Figures (7)

• Figure 1: (a) Plot of staggered magnetisation $M_s$ versus temperature ($T$) for five different values of impurity concentrations. (b) The scaled staggered magnetisation ($M_s p^b$) is plotted against scaled reduced temperature ($(T-T_c)p^a$. The best estimates are $T_c=4.45$, $a=-0.95$ and $b=0.09$ for data collapse. (c) The zero temperature (extrapolated) staggered magnetisation ($M_s(0)$ is plotted against impurity concentrations ($p$). The best fitted ($M_s(0)=mp+c$) parameter values are $m=-1.029$ and $c=1.007$. Here, $h_i=0$.
• Figure 2: The staggered susceptibility ($\chi$) is plotted against the temperature($T$) for five different values of the nonmagnetic impurity concentrations ($p$), in the absence of any magnetic field ($h_i=0.0$). Here, the system size $L=20$.
• Figure 3: The staggered susceptibility $\chi$ is plotted against the temperature($T$) for five different values of system size ($L$) for $p=0.3$. Here, $h_i=0$.
• Figure 4: The critical temperature ($T_c$) is plotted against the nonmagnetic impurity concentrations ($p$), in the absence of any magnetic field ($h_i=0.0$). The solid straight line represents the best fitted ($T_c=mp+c$, with $m \cong -5.536$ and $p \cong 4.601$) curve.
• Figure 5: The staggered magnetisation ($M_s$), of pure ($p=0$) Ising metamagnet, is plotted against the temperature ($T$) for five different values of the width ($s$) of the uniformly distributed random magnetic field.