Magnetoelectric Effect in Garnet Mn 3 Al 2 Ge 3 O 12 .

Searching for novel magnetoelectric (ME) materials has been one of the major issues of multiferroics. In this work, we present a systematic research study on garnet Mn 3 Al 2 Ge 3 O 12 , including structural, magnetic, heat capacity, and ME characterizations. Below the Néel temperature T N ∼ 6.8 K, Mn 2+ spins form a long-range antiferromagnetic order, and a magnetic field H -driven electric polarization P is identified simultaneously. The relationship between P and H is nonlinear under low H and becomes linear under high H . Such transition is believed to originate from the H -induced variation of the magnetic structure. In addition, the P reaches 0.6 μC/m 2 under μ 0 H = 9 T, corresponding to an ME coupling coefficient of α ME ∼ 0.08 ps/m under high H . The small α ME is attributed to the weak spin-orbit coupling and weak magnetic interactions in Mn 3 Al 2 Ge 3 O 12 . Furthermore, we realize the stable control of P by periodically varying H , which is crucial for potential application. We provide a rare case that a garnet material shows a first-order ME effect.