Poling magnetic field dependence and memory effect of magnetoelectric coupling in honeycomb antiferromagnet cobalt niobate

We have firstly studied the poling magnetic field dependence of magnetoelectric (ME) coupling in a honeycomb antiferromagnet Co 4 Nb 2 O 9 , and found that the ME susceptibilities do not increase monotonously with increasing the poling magnetic field strength ( H Pole ) as the usual case, but reach maxima around 10 kGs. This phenomenon results from opposite H Pole dependences of domain wall thickness and energitically preferred domain's proportion. More interestingly, if the sample returns to paramagnetic phase after being poled and then reenters antiferromagnetic phase without being poled, ME coupling still exists. This memory effect is attributed to the presence of ME domain nucleation centers in paramagnetic phase.