Magnetocapacitance effect and magnetoelectric coupling in type-II multiferroic HoFeWO6

Abstract

We have investigated the multiferroicity and magnetoelectric (ME) coupling in HoFeWO 6 . With a noncentrosymmetric polar structure (space group Pna2 1 ) at room temperature, this compound shows an onset of electric polarization with an antiferromagnetic ordering at the Néel temperature (T N ) of 17.8 K. 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 of the compound. In particular, field-dependent measurements of capacitance show a magnetocapacitance (MC) effect with double-hysteresis loop behavior in direct correspondence with the magnetization. Our x-ray diffraction results show the Pna2 1 structure down to 8 K and suggest the absence of a structural phase transition across T N . Soft x-ray absorption spectroscopy and soft x-ray magnetic circular dichroism (XMCD) measurements at the Fe L 2,3 and Ho M 4,5 edges revealed the oxidation state of Fe and Ho cations to be 3+. Fe L 2,3 XMCD further shows that Fe 3+ cations are antiferromagnetically ordered in a noncollinear fashion with spins arranged 90 • with respect to each other. Our findings show that HoFeWO 6 is a type-II multiferroic exhibiting a MC effect. The observed MC effect and the change in polarization by the magnetic field, as well as their direct correspondence with magnetization, further support the strong ME coupling in this compound.

Magnetocapacitance at the Ni/BiInO3 Schottky Interface

“…As noted at the outset, magnetocapacitance occurs when the capacitance of a device changes with respect to the applied magnetic field. The coupling of ferroelectricity and ferromagnetism is common in multiferroic materials that can lead to magnetocapacitance effects, − yet the BiInO 3 thin films discussed here are nonpolar, so this does not apply to the Ni/BiInO 3 /(Ba,Sr)­RuO 3 /NdScO 3 (110) o heterostructure discussed here. Again, as noted at the outset, according to the Maxwell–Wagner capacitor model, − nonmultiferroic materials can also exhibit magnetocapacitance effects.…”

“…Applied magnetic field-controlled capacitance effects are common to multiferroic materials and ferromagnetic/ferroelectric multilayer stacks, leveraging the coexistence and coupling of more than one ferroic order parameter, principally magneto-electric coupling. − It is now understood that with the generalization of the Maxwell–Wagner capacitor model, magnetocapacitance effects are possible even in nonmultiferroic materials. − Magnetocapacitance effects are expected in nonmultiferroic materials as a result of giant intrinsic magneto-resistance, interface effects, and bulk inhomogeneities …”