Magnetoimpedance spectroscopy of epitaxial multiferroic thin films

Abstract

The detection of true magnetocapacitance (MC) as a manifestation of magnetoelectric coupling (MEC) in multiferroic materials is a nontrivial task, because pure magnetoresistance (MR) of an extrinsic MaxwellWagner-type dielectric relaxation can lead to changes in capacitance [G. Catalan, Appl. Phys. Lett. 88, 102902 (2006)]. In order to clarify such difficulties involved with dielectric spectroscopy on multiferroic materials, we have simulated the dielectric permittivity ε of two dielectric relaxations in terms of a series of one intrinsic film-type and one extrinsic Maxwell-Wagner-type relaxation. Such a series of two relaxations was represented in the frequency-(f -) and temperature-(T -) dependent notations ε vs f and ε vs T by a circuit model consisting in a series of two ideal resistor-capacitor (RC) elements. Such simulations enabled rationalizing experimental f -, T-, and magnetic field-(H -) dependent dielectric spectroscopy data from multiferroic epitaxial thin films of BiMnO 3 (BMO) and BiFeO 3 (BFO) grown on Nb-doped SrTiO 3 . Concomitantly, the deconvolution of intrinsic film and extrinsic Maxwell-Wagner relaxations in BMO and BFO films was achieved by fitting f -dependent dielectric data to an adequate equivalent circuit model. Analysis of the H -dependent data in the form of determining the H -dependent values of the equivalent circuit resistors and capacitors then yielded the deconvoluted MC and MR values for the separated intrinsic dielectric relaxations in BMO and BFO thin films. Substantial intrinsic MR effects up to 65% in BMO films below the magnetic transition (T C ≈ 100 K) and perceptible intrinsic MEC up to − 1.5% near T C were identified unambiguously.

Dielectric properties of (Bi0.9La0.1)2NiMnOLangenberg1, Fina2, Ventura3 et al. 2012Phys. Rev. B

“…3), C is commonly replaced by a constant phase element (CPE). 10,[25][26][27] The impedance of this R-CPE circuit is given by…”

“…10,[25][26][27][28] Capacitance values, C, can be obtained according to the relationship C = (Q · R)…”

“…Yet many multiferroic materials tend to be poor insulators, preventing a sufficient electric field from being applied 9,10 and thus hampering experimental determination of the magnetoelectric coupling. An alternative route to investigating the magnetoelectric character consists of studying the effect on the dielectric permittivity ε of changes of the magnetic state of the magnetic layer-either by applying a magnetic field, the so-called magnetocapacitance, or by searching for variations of ε in the temperature dependence ε(T ) in the vicinity of the magnetic transition temperature.…”

“…3 Here, we report on a quantitative study of the apparent temperature-dependent dielectric relaxation of BLNMO thin films, which we prove is driven by the temperature dependence of the resistivity instead of the dielectric relaxation of electric dipoles. Impedance spectroscopy methods 10,12,20 have been used to disentangle extrinsic contributions to the measured permittivity and to extract the temperature dependence of the intrinsic dielectric and resistive properties of (Bi 0.9 La 0.1 ) 2 NiMnO 6 films. Moreover, we show that the magnetocapacitance of (Bi 0.9 La 0.1 ) 2 NiMnO 6 films is likely due to extrinsic effects, suggesting a weak intrinsic magnetoelectric coupling in (Bi,La) 2 NiMnO 6 compounds.…”

Magnetoelectric coupling of multiferroic chromium doped barium titanate thin film probed by magneto-impedance spectroscopy

“…13,14 Deconvolution of intrinsic film and extrinsic Maxwell-Wagner relaxation in BiMnO 3 and BiFeO 3 films were attained by fitting frequency dependent data to an adequate equivalent circuit model. 15 In single crystal LuFe 2 O 4 , origin of magnetoelectric effect by interfacial effect was ruled out by impedance spectroscopy. 16 In this work, single phase Cr:BTO thin film has been investigated for magnetoelectric coupling at room temperature.…”