Spontaneous Magnetization

Spontaneous magnetization $m$ in an Ising ferromagnet appears below the critical temperature $T_c$. The derivative of $m$ diverges in the limit $T \to T_c^-$.

Edit and compile if you like:

% Spontaneous magnetization m in an Ising ferromagnet appears below the critical temperature T_c.
% The derivative of m diverges in the limit $T \to T_c^-$.

\documentclass{standalone}

\usepackage{pgfplots}

\begin{document}
\begin{tikzpicture}[
declare function={
% arcsinh
arcsinh(\x) = ln(\x + sqrt(\x^2+1));
% magnetization
m(\x) = and(\x>=0,\x<1) * (1 - (sinh(arcsinh(1)/x))^(-4))^(1/8) + or(\x<0,\x>=1) * (0);
}]

\begin{axis}[
xlabel = {$T/T_c$},
ylabel = {$m(0,T)$},
smooth,thick,
domain=0:1.8,
ymax=1.6,
axis lines = center,
every tick/.style = {thick}]