Magnons and magnetodielectric effects in CoCr2O4 : Raman scattering studies

Abstract

Magnetoelectric materials have generated wide technological and scientific interest because of the rich phenomena these materials exhibit, including the coexistence of magnetic and ferroelectric orders, magnetodielectric behavior, and exotic hybrid excitations such as electromagnons. The multiferroic spinel material, CoCr2O4, is a particularly interesting example of a multiferroic material, because evidence for magnetoelectric behavior in the ferrimagnetic phase seems to conflict with traditional noncollinear-spin-driven mechanisms for inducing a macroscopic polarization. This paper reports an inelastic light scattering study of the magnon and phonon spectrum of CoCr2O4 as simultaneous functions of temperature, pressure, and magnetic field. Below the Curie temperature (TC ∼ 94 K) of CoCr2O4 we observe a ω ∼ 16 cm −1 q = 0 magnon having T1g-symmetry, which has the transformation properties of an axial vector. The anomalously large Raman intensity of the T1g-symmetry magnon is characteristic of materials with a large magneto-optical response and likely arises from large magnetic fluctuations that strongly modulate the dielectric response in CoCr2O4. The Raman susceptibility of the T1g-symmetry magnon exhibits a strong magnetic-field dependence that is consistent with the magnetodielectric response observed in CoCr2O4, suggesting that magnetodielectric behavior in CoCr2O4 primarily arises from the field-dependent suppression of magnetic fluctuations that are strongly coupled to long-wavelength phonons. Increasing the magnetic anisotropy in CoCr2O4 with applied pressure decreases the magnetic field-dependence of the T1g-symmetry magnon Raman susceptibility in CoCr2O4, suggesting that strain can be used to control the magnetodielectric response in CoCr2O4.

van der Waals Magnets: Material Family, Detection and Modulation of Magnetism, and Perspective in Spintronics

“…The introduction of magnetic order may induce magnetic excitations [ 115 ] and modulate the phonon behaviors [ 62 ] of vdW magnets, resulting in phenomena like magnons, [ 116 ] spin‐phonon coupling, [ 72 ] and Brillouin zone folding, [ 55 ] which can be detected by Raman spectrum. Compared with the methods listed above, Raman measurements are very important in the characterization of magnetism in both FM and AFM vdW magnets with in‐plane or out‐of‐plane magnetization.…”

Dielectric and ferroelectric properties of CoCr2O4 nanoceramics

“…In CoCr 2 O 4 , Co 2þ ions exists at A (tetrahedral) sites and Cr 3þ ions are at B (octahedral) sites. It has been reported that CoCr 2 O 4 has shown successive magnetic orders at different temperatures such as ferrimagnetic phase occurs below T C … 92-94 K, incommensurate conical spiral order below T S … 26 K and commensurate order below T L … 26 K. [5][6][7] Generally, for these type-II multiferroics, the electrical polarization is much smaller ($ 10 À2 C/cm 2 ) than in type-I multiferroics ($ 10-100 C/cm 2 ). Particularly in BiFeO 3 (T C $ 1100 K, T N $ 643 K, P $ 90 C/cm 2 ) and YMnO 3 (T C $ 914 K, T N $ 76 K, P $ 6 C/cm 2 ) the FE Curie temperature (T C ) is much higher than the magnetic ordering temperature (T N ).…”

Quasi-two-dimensional magnon identification in antiferromagneticFePS3via magneto-Raman spectroscopy

“…22 Raman spectroscopy, being non-destructive and highly sensitive to minute perturbations, is a powerful technique to study various properties of quantum materials, including the effects of layer number, 33,34 strain, 35 defects/doping, 36 electron-phonon coupling, 37,38 phase transitions, 39 spin-phonon coupling, 40 and magnetic excitations. 41,42 In addition, unlike other measurements that require bulk, large-area crystals, such as neutron diffraction, X-ray diffraction, or magnetic susceptibility, Raman spectroscopy can probe atomically thin flakes with diffraction-limited spatial resolution. The Raman spectra of bulk XPS3 materials has been studied since the 1980's, 28,43,44 and only recently extended to samples in the monolayer limit for NiPS3 45 and FePS3.…”