Distinct magneto-Raman signatures of spin-flip phase transitions in CrI3

Abstract

The discovery of 2-dimensional (2D) materials, such as CrI 3 , that retain magnetic ordering at monolayer thickness has resulted in a surge of both pure and applied research in 2D magnetism. Here, we report a magneto-Raman spectroscopy study on multilayered CrI 3 , focusing on two additional features in the spectra that appear below the magnetic ordering temperature and were previously assigned to high frequency magnons. Instead, we conclude these modes are actually zone-folded phonons. We observe a striking evolution of the Raman spectra with increasing magnetic field applied perpendicular to the atomic layers in which clear, sudden changes in intensities of the modes are attributed to the interlayer ordering changing from antiferromagnetic to ferromagnetic at a critical magnetic field. Our work highlights the sensitivity of the Raman modes to weak interlayer spin ordering in CrI 3 .

Quantum Engineering With Hybrid Magnonic Systems and Materials (Invited Paper)

“…The tensor forms of coefficients K αβµ (R), G αβµν (R), and L αβµν (R, r) are subject to the crystallographic symmetry of the magnetic system. 277 Below, we will focus on three types of magnetic excitations in 2D vdW and SOC magnetic systems: (a) phonons coupled to the static magnetic order that correspond to time-reversal-symmetry (TRS) broken antisymmetric Raman tensors, [278][279][280][281][282] (b) single magnon excitations that contain contributions from both the first and second terms in Eq. (15), 283,284 and (c) two-magnon excitations involving pairs of magnons from the Brillouin zone boundaries and center.…”

“…[286][287][288] While early studies have focused on magnetic ordering in single-and few-layer samples using static magneto-optics 286,287,[289][290][291][292][293][294] (i.e., magneto-optical Kerr effect (MOKE) and magnetic circular dichroism (MCD)) as well as tunneling magnetoresistance, [295][296][297][298] optical magneto-Raman spectroscopy has contributed unique insights into the dynamic magnetic excitations in 2D vdW magnets. [278][279][280][281][282][283][284] SOC magnetism refers to magnetic systems where SOC is at an energy scale comparable to that of electronic correlations, 299,300 and it is primarily realized in 5d transition metal oxides (TMOs), such as iridium oxides. 301,302 While the spin dynamics of 5d TMOs have been primarily probed by hard xray scattering [303][304][305][306][307][308][309][310][311] and neutron scattering [312][313][314] (if the sample volume is large enough to overcome the challenges posed by the strong neutron absorption by Ir), optical magneto-Raman spectroscopy has provided complementary information thanks to its superior energy resolution and clean selection rules.…”

Low Energy Electrodynamics of CrI3 Layered Ferromagnet

“…Indeed, CrI 3 layers can be described by the D 3d point group symmetry 29,52 , which predicts five IRallowed transitions, namely three E u modes and two A 2u modes, three inactive modes (one A 1u and two A 2g ), and six Raman-active modes (two A 1g and four E g ). Raman spectra at room-T have already been measured in pre-vious works and the corresponding peaks are reported in Table II together with numerical calculations (at 0 K) [53][54][55] and the IR absorption peaks observed at room-T in our experiment, as measured by absorption peak maxima. In the theoretical calculation, the heavier iodine atoms are predicted to dominate the phonon spectrum below 150 cm −129,56 , therefore being related to the strong absorption peaks at 82 and 114 cm −1 (E u modes) and 133 cm −1 (A 2u mode).…”

“…CrI3 vibrational modes frequencies (in cm −1 ) at 300 K. The values in the quadratic brackets highlight the inplane Raman-and IR-active modes at 0 K, as obtained by DFT results29 . The first column shows the experimental Raman modes54,55 . The IR-active experimental modes obtained in this work are shown in the second and third columns.…”

Twist engineering of the two-dimensional magnetism in double bilayer chromium triiodide homostructures

“…Magneto-Raman spectroscopy can capture the interlayer magnetism in few-layer CrI3, by detecting the unique static magnetism-coupled phonons that break the time-reversal symmetry and have antisymmetric Raman tensors [38][39][40][41][42] , in addition to the conventional pure structural phonons. Figure 1d presents representative Raman spectra of tDB CrI3 with the targeted = 1.1 o in both the crossed and parallel linear polarization channels at 10 K, featuring key Raman modes in three spectral ranges, 75 to 85 cm -1 , 95 to 120 cm -1 , and 120 to 133 cm -1 .…”