Opposite-axis quadratic anisotropy of a vector order parameter
= Opposite-axis quadratic anisotropy of a vector order parameter
{title2=$f=\tfrac12t|m|^2+u|m|^4+\tfrac12r(m_1^2-m_2^2)$}
For $u>0$ and $t>0$, minimizing a uniform field gives zero magnetization when $|r|\leq t$. For $r<-t$ only component 1 orders, with $m_1^2=-(t+r)/(4u)$; for $r>t$ only component 2 orders, with $m_2^2=(r-t)/(4u)$. Both transition lines are continuous. The positive-$t$ disordered wedge separates the two easy-axis phases.