We present a unique example of giant magnetoelectric effect in a conventional multiferroic HoMnO3, where polarization is very large (~56 mC/m2) and the ferroelectric transition temperature is higher than the magnetic ordering temperature by an order.
We attribute the uniqueness of the giant magnetoelectric effect to the ferroelectricity induced entirely by the off-center displacement of rare earth ions with large magnetic moments. This finding suggests a new avenue to design multiferroics with large polarization and higher ferroelectric transition temperature as well as large magnetoelectric effects.
Spin correlations in the pyrochlore antiferromagnet Y_2Ru_2O_7 with Curie-Weiss temperature $Theta_{CW}=-1100$ K and critical temperature T_N=77 K were examined through neutron scattering. For $T_N<T<Theta_{CW}/3$ the data show spin relaxation with a
rate $hbarGamma= 1.17(9)k_BT$. For T<T_N spectral weight moves to higher energies with substantial changes up to $4times k_BT_N$. For T<<T_N there is a $Delta=11(1)$ meV energy gap and a pronounced spectral maximum at 19.7 meV. Throughout the temperature range examined the wave vector dependence of inelastic scattering exhibits a broad peak for $Qdapprox 3.8$ (d is Ru-Ru spacing) consistent with dipolar spin correlations.
