On the structural origin of the single-ion magnetic anisotropy in LuFeO₃

Abstract

The electronic structure for the conduction bands of both hexagonal and orthorhombic LuFeO3 thin films have been measured using x-ray absorption spectroscopy at oxygen K (O K) edge. Dramatic differences in both the spectral features and the linear dichroism are observed. These differences in the spectra can be explained using the differences in crystal field splitting of the metal (Fe and Lu) electronic states and the differences in O 2p-Fe 3d and O 2p-Lu 5d hybridizations. While the oxidation states have not changed, the spectra are sensitive to the changes in the local environments of the Fe(3+) and Lu(3+) sites in the hexagonal and orthorhombic structures. Using the crystal-field splitting and the hybridizations that are extracted from the measured electronic structures and the structural distortion information, we derived the occupancies of the spin minority states in Fe(3+), which are non-zero and uneven. The single ion anisotropy on Fe(3+) sites is found to originate from these uneven occupancies of the spin minority states via spin-orbit coupling in LuFeO3.

Phase separation in LuFeO3 films

“…21 For o-LuFeO 3 , the absorption spectra always show two peaks, in the region of 708 to 712 eV, corresponding to the e g and t 2g crystal field states, independent of polarization of X-ray. 16,17 Therefore, there is a clear correlation between lattice structure and X-ray absorption spectra in LuFeO 3 . 18 In particular, with s-polarized X-ray, the difference between the absorption spectra of h-LuFeO 3 and o-LuFeO 3 is significant, an aid for distinguishing the two structural phases.…”

“…1 Hexagonal LuFeO 3 (001) films were grown on Al 2 O 3 (0001) substrates using pulsed laser deposition at 750 C in a 5 mTorr oxygen environment. 1, [16][17][18] To test the thermal stability of hexagonal LuFeO 3 , we carried out a sequence of annealing on a film sample of $40 nm thickness. For each annealing step, the temperature was raised slowly (5 C/min) from room temperature to the annealing temperature (T A ) and then annealed at that temperature for 3 h, followed by a slow cooldown (5 C/min) to room temperature.…”

“…This same sample was also investigated by X-ray absorption spectroscopy (XAS) studies through the X-ray photoemission electron microscope (X-PEEM), at the SM beamline of the Canadian Light Source (CLS) with linearly polarized X-rays at room temperature in ultrahigh vacuum; the X-ray beam incident angle was 16 . 17 The XAS was obtained by pixel-by-pixel integration of X-PEEM image as a function of photon energy.…”

“…As recently demonstrated, 16,17 the X-ray absorption spectra of the hexagonal and orthorhombic phases are dramatically different, both in spectral shape and in linear dichroism, and these differences in the X-ray absorption spectra (XAS) may be used to distinguish the two phases. 16,17 X-PEEM technique, employing a tunable Xray source and an electron microscope, measures the X-ray absorption spectra with spatial resolution, 20 so is an ideal technique to conclusively distinguish the two structural phases in real space, by comparing the X-ray absorption spectra at various spatial locations point by point. Figure 2(a) presents the X-ray absorption spectra at Fe L III and L II edges for h-LuFeO 3 and o-LuFeO 3 using linearly polarized X-rays.…”

“…16,18 The energies of these crystal field states follow the order E a 0 1 > E e 0 > E e 00 . 17 As shown in Fig. 2(a), for h-LuFeO 3 , the XAS e 0 peak (at about 709.5 eV) will only be present with s polarization (i.e., with in-plane linearly polarized light), 18 due to the applicable spectroscopic selection rules.…”