Evidence of three-dimensional Ising ferromagnetism in theA-site-ordered perovskite CaCu3Ge4O12

Abstract

The $A$-site-ordered perovskite CaCu${}_{3}$Ge${}_{4}$O${}_{12}$ synthesized under high pressure undergoes ferromagnetic spin ordering below ${T}_{c}$ \ensuremath{\approx} 12 K. The critical exponents have been determined from isotherms of magnetization across ${T}_{c}$ via an iteration process and the Kouvel-Fisher method as well as from specific heat. Based on fitting parameters of ${T}_{c}$, $\ensuremath{\beta}$, and $\ensuremath{\gamma}$, the magnetization data in the vicinity of ${T}_{c}$ can be scaled onto two universal curves in the plot of $M$/|\ensuremath{\varepsilon}|${}^{\mathrm{\ensuremath{\beta}}}$ vs $H$/|\ensuremath{\varepsilon}|${}^{\mathrm{\ensuremath{\beta}}+\mathrm{\ensuremath{\gamma}}}$, where $\ensuremath{\varepsilon}$ $=$ $T/{T}_{c}$\ensuremath{-}1. Critical exponents $\ensuremath{\alpha}$, $\ensuremath{\beta}$, and $\ensuremath{\gamma}$ obtained indicate that CaCu${}_{3}$Ge${}_{4}$O${}_{12}$ is a three-dimensional coupled Ising ferromagnet with a small coercivity.