Intrinsic electrical properties of LuFe2O4

Abstract

We here revisit the electrical properties of LuFe 2 O 4 , compound candidate for exhibiting multiferroicity. Measurements of dc electrical resistivity as a function of temperature, electric-field polarization measurements at low temperatures with and without magnetic field, and complex impedance as a function of both frequency and temperature were carried out in a LuFe 2 O 4 single crystal, perpendicular and parallel to the hexagonal c axis, and in several ceramic polycrystalline samples. Resistivity measurements reveal that this material is a highly anisotropic semiconductor, being about two orders of magnitude more resistive along the c axis. The temperature dependence of the resistivity indicates a change in the conduction mechanism at T CO ≈ 320 K from thermal activation above T CO to variable range hopping below T CO . The resistivity values at room temperature are relatively small and are below 5000 cm for all samples but we carried out polarization measurements at sufficiently low temperatures, showing that electric-field polarization curves are a straight line as expected for a paraelectric or antiferroelectric material. Furthermore, no differences are found in the polarization curves when a magnetic field is applied either parallel or perpendicular to the electric field. The analysis of the complex impedance data corroborates that the claimed colossal dielectric constant is a spurious effect mainly derived from the capacitance of the electrical contacts. Therefore, our data unequivocally evidence that LuFe 2 O 4 is not ferroelectric.

Strong local lattice instability in hexagonal ferritesRFe2O4(R= Lu,Y,Yb) revealed by x-ray absorption spe

“…In this way, for LuFe 2 O 4 and YFe 2 O 4 , below T CO , different fractional charges are localized in the lattice giving rise to an ordered sequence of charges, and larger discontinuities are observed in the crystal structure. On the contrary, a random distribution [59] or an incommensurate ordering seems to occur for the YbFe 2 O 4 compound [16], which remains in the hexagonal crystallographic structure even at low temperatures. Finally, the local structure instability should have an important role in the electrical properties, but their correlation with the kind of charge order is a matter of future studies.…”

“…On one hand, the claimed colossal dielectric constants are spurious effects originating from the electrical contacts [37][38][39], and on the other hand, LuFe 2 O 4 does not show spontaneous electrical polarization, as has been proved by electrical polarization measurements [39]. Although the occurrence of ferroelectricity can be discarded in LuFe 2 O 4 , the structural phase transition at T CO 320 K is still considered to originate from Fe 3+ /Fe 2+ CO. Resonant x-ray scattering (RXS) experiments at the Fe K-edge of the principal observed superstructure (1/3, 1/3, half-integer) reflections seem to support this assumption, but the analysis performed by either Ikeda et al [7] or Mulders et al [40] are merely qualitative, using a generic structure factor without considering any charge order sequence.…”

Electronic states ofRFe2O4(R=Lu,Yb,TmLafuerza1, García2, Subı́as3 et al. 2014Phys. Rev. BSelf Cite10241View full textAdd to dashboardCite

“…All the samples show a sharp transition at T N ≈ 250−240 K for H = 0.1 T (not shown here), in agreement with the expected ferrimagnetic ordering and a large low temperature coercivity. Thermal and electrical properties as a function of temperature for the studied RFe 2 O 4 (R = Lu, Yb, Tm, Y) samples show the anomalies at the phase transition temperatures expected for stoichiometric compounds [10,41,42].…”

“…Despite the widespread belief in the existence of ferroelectricity in LuFe 2 O 4 , recent results have challenged both the polar character and the existence of pure ionic CO. It has been demonstrated that the colossal dielectric permittivity is originated by the electrical contacts [39][40][41] and that LuFe 2 O 4 does not show spontaneous electrical polarization in the P (E) loops [41]. In addition, x-ray absorption spectroscopy (XAS) experiments at the Fe K edge have shown that the charge segregation between the different iron atoms cannot be larger than 0.5 electrons [42].…”

“…Regarding the formerly reported XAS/XMCD works in LuFe 2 O 4 , we here present the following results: (i) a complete XAS characterization at the O K edge and Fe L 2,3 edges since our data include RFe 2 O 4 (R = Yb, Tm, Y) and LuFeCoO 4 samples, (ii) XMCD spectra at the Fe L 2,3 edges with the magnetic field applied both parallel and perpendicular to the c axis, and (iii) XMCD spectra at the Fe K edge, not reported before to the best of our knowledge. [41]). All samples were analyzed by x-ray diffraction being single phase.…”