MAGNETOCAPACITANCE EFFECT AND MAGNETOELECTRIC COUPLING IN TYPE-II MULTIFERROICS RFeWO6 (R = Ho, Dy, and Tb)

In this work, we have studied the multiferroic behavior and magnetoelectric (ME) coupling in a group of oxides, RFeWO6 (R = Ho, Dy, and Tb). These compounds have a non-centrosymmetric polar structure (space group Pna21) at room temperature and exhibit an onset of an improper ferroelectric transition with an antiferromagnetic ordering at the Neel temperature (TN). The magnetic properties of the polycrystalline samples were studied by DC and AC magnetization and heat capacity measurements. The metamagnetic behavior at low temperatures was found to be directly related to the dielectric properties and polarization of the compounds. We observed that the field-dependent measurements of capacitance show a magnetocapacitance (MC) effect with double-hysteresis loop behavior, which is in direct correspondence with the magnetization. Our X-ray diffraction results on HoFeWO6 show the Pna21 structure down to 8 K and suggest the absence of a structural phase transition across TN. The structural relaxation calculation of HoFeWO6 also shows that the Pna21 is the stable structure. The total density of states of this compound also demonstrate an insulating state with a wide band gap of ~3.7 eV. Soft X-ray absorption spectroscopy and soft X-ray magnetic circular dichroism (XMCD) measurements at the Fe L2, 3 and R (= Ho, Dy, and Tb) M4, 5 edges revealed the oxidation state of Fe and R (= Ho, Dy, and Tb) cations to be 3+. Fe L2, 3 XMCD further shows that Fe3+ cations are antiferromagnetically ordered in a non-collinear fashion with spins arranged 90 degrees with respect to each other. Our findings show that HoFeWO6, in addition to DyFeWO6 and TbFeWO6 is also a type-II multiferroic and they all exhibit an MC effect. The observed MC effect and the change in polarization by the magnetic field, in addition to their direct correspondence with magnetization, further support the strong ME coupling in this compound.