Magnetic and dielectric response of cobalt-chromium spinel CoCr2O4 in the terahertz frequency range

Abstract

The nature of the phonon and magnon modes in the CoCr 2 O 4 multiferroic with a cubic spinel structure has been studied using submillimeter spectroscopy and infrared Fourier spectroscopy. This paper reports on the first measurement of the evolution with temperature of the exchange optical magnon in the ferrimagnetic (T C = 94 K) and two low symmetry (T S ≈ 26 K, T lock in = 14.5 K) phases of CoCr 2 O 4 down to T = 5 K in zero magnetic field. It has been shown that the detected magnon is not a ferrimagnetic order parameter and originates, most probably, from spin precession in the cobalt sublattices. At the points of the magnetic phase transitions, the oscillator parameters of the two lowest frequency phonon modes reveal an anomalous temperature behavior, thus evidencing the presence of significant interaction between the mag netic and phonon subsystems. The increase by 25% of the damping parameter of the phonon mode originat ing from vibrations of the CoO 4 tetrahedra during the transition of CoCr 2 O 4 to the multiferroic state (T < T S ) suggests structural changes in the lattice involving loss of spatial central symmetry of the medium.

Ferroelectricity in spinel solid solution Co0.8Ni0.2Cr2OБуш1, Shkuratov2, Kamentsev3 et al. 2012Phys. Rev. BSelf Cite141110View full textAdd to dashboardCite

“…The obtained symmetry and dimensions of the solid solutions unit cells are in accordance with the literature data on the spinel CoCr 2 O 4 and NiCr 2 O 4 phases. 7,11,13,14,21,22 Thus, the x-ray analysis shows that the samples are single phase and belong to the spinel structural type.…”

“…In ACr 2 O 4 , the transition into the ferrimagnetic state takes place at T N = 93 K for A = Co and at T N = 70 К for A = Ni. 6,9,11,[20][21][22] In spite of the fact that the considered complex oxides reveal intriguing elastic, electrical, magnetic, catalytic, and other physical properties and attract much attention, there is practically no data in the literature on their dielectric characteristics. In this paper we present our results on the first measurements of the temperature-frequency behavior of the complex dielectric permittivity ε * = ε 1 + iε 2 , loss tangent tgδ = ε 2 /ε 1 , and of thermally stimulated depolarization (TSDP) currents of the ceramic samples Co 1−x Ni x Cr 2 O 4 with different nickel contents x.…”

Observation of an intersublattice exchange magnon in CoCr2O4and analysis of magnetic ordering

“…5 As multiferroics are appealing because of basic physical interest as well as their potential technological applications, 6 the reported multiferroicity of CoCr 2 O 4 has triggered a number of experimental studies of the compound. 4,[7][8][9][10] To date, there is, however, no optical data reported at terahertz frequencies. This is the frequency region where, e.g., electromagnons have been observed in some other multiferroic systems.…”

“…20 The measurements were performed in the Faraday geometry (k H ⊥h) at 4 and 30 K. A mercury lamp was used as a radiation source. The far-infrared radiation was detected using a custom-made silicon bolometer operating at 1.4 K. For both temperatures, the FTIR spectra were measured in 0, 3,5,8,10,12,15,17,20,25, and 30 T. The optical data were collected between 15 and 70 cm −1 (450 ÷ 2100 GHz, 1.9 ÷ 8.7 meV), using a 200-μm mylar beamsplitter and a scanning velocity of 50 kHz. At each field, at least 100 scans were averaged.…”

Magnons and magnetodielectric effects in CoCr2O4 : Raman scattering studies

“…Rietveld refinement of the CoCr 2 O 4 cell to the XRD data was performed using XND Rietveld, 45 and indicates a pure sample with F d3m symmetry and a lattice constant of 8.334(1)Å, which agrees with the established structure. 28 The < 110 > reflections from a single crystal of CoCr 2 O 4 were measured, and no evidence of twinning imperfections was found. The field-cooled dc magnetization data on the CoCr 2 O 4 powder from which our crystal sample was obtained was collected using a Quantum Design MPMS-3 and is shown as a function of temperature in Fig.…”