Anharmonic effects in ferromagnetic semiconductors

The Raman-active phonons and magnetic excitations in the orbitally ordered, quasi-one-dimensional Heisenberg antiferromagnet KCuF 3 are studied as a function of temperature in the range between 3 and 290 K in various scattering configurations. The low-energy E g and B 1g phonon modes show an anomalous softening (~25% and ~13%) between room temperature and the characteristic temperature T S = 50 K. In this temperature range a freezing-in of F -ion dynamic displacements is proposed to occur. In addition, the E g mode at about 260 cm -1 clearly splits below T S . The widths of the phonon lines above T S follow an activated behavior with an activation energy of about 50 K. Our observations clearly evidence a reduction of the lattice symmetry below T S and indicate a strong coupling of lattice, spin, and orbital fluctuations for T > T S . A strongly polarization dependent quasielastic scattering is observed at temperatures above T N = 39 K due to magnetic-energy fluctuations. For temperatures below T N a rich spectrum of additional modes is observed, with different lineshape, polarization and temperatures dependence. We attribute them to longitudinal and transverse magnetic modes as well as to a continuum of magnetic excitations.

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“…In magnetic materials, the frequency change of a phonon i with temperature can be written as [36][37][38][39][40] ( ) ( ) ( ) ( ) ( )…”

Section: Raman Phononsmentioning

confidence: 99%

Phononic and magnetic excitations in the quasi-one-dimensional Heisenberg antiferromagnet KCuF3

Gnezdilov

Lemmens

Wulferding

et al. 2012

Low Temperature Physics

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“…34 These authors have shown that the frequency shift of a given phonon mode as function of temperature is determined by a spin-correlation function…”

Section: Spin-phonon Couplingmentioning

confidence: 99%

“…34 These authors show that in the magnetically ordered phase an additional contribution to the phonon damping arises due to spin-phonon interactions, which vanishes in the paramagnetic phase. …”

Section: Spin-phonon Couplingmentioning

confidence: 99%

Polar phonons and spin-phonon coupling inHgCr2S4andCdC

et al. 2007

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Polar phonons of HgCr2S4 and CdCr2S4 are studied by far-infrared spectroscopy as a function of temperature and external magnetic field. Eigenfrequencies, damping constants, effective plasma frequencies and Lyddane-Sachs-Teller relations, and effective charges are determined. Ferromagnetic CdCr2S4 and antiferromagnetic HgCr2S4 behave rather similar. Both compounds are dominated by ferromagnetic exchange and although HgCr2S4 is an antiferromagnet, no phonon splitting can be observed at the magnetic phase transition. Temperature and magnetic field dependence of the eigenfrequencies show no anomalies indicating displacive polar soft mode behavior. However, significant effects are detected in the temperature dependence of the plasma frequencies indicating changes in the nature of the bonds and significant charge transfer. In HgCr2S4 we provide experimental evidence that the magnetic field dependence of specific polar modes reveal shifts exactly correlated with the magnetization showing significant magneto-dielectric effects even at infrared frequencies.

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“…Spin-phonon coupling has been described by many authors. [10][11][12][13] These authors have shown that the frequency shift of a given phonon mode is determined by spin-correlation function: ω = ω 0 + λ⟨S i • S j ⟩. Here, ω is the renormalized phonon frequency, ω 0 is eigenfrequency in the absence of spin-phonon coupling, λ is spin-phonon coupling constant.…”

mentioning

confidence: 99%

Magnetodielectric and magnetoelastic coupling in Co4Nb2O9 below Néel temperature

et al. 2016

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The dielectric constant of Co4Nb2O9 shows an obvious upturn below Néel temperature (TN), and the magnetic field enhances this anomaly. Thus the magnetodielectric effect exists in the entire temperature region below TN, not only near TN as reported previously. At the same time, the strain exhibits a drop below TN, and the magnetic field suppresses this anomaly, demonstrating magnetoelastic coupling in Co4Nb2O9. The origin of dielectric anomaly and magnetodielectric effect below TN may be related to the phonon mode shifts induced by magnetoelastic coupling.

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Anharmonic effects in ferromagnetic semiconductors

Cited by 45 publications

References 12 publications

Phononic and magnetic excitations in the quasi-one-dimensional Heisenberg antiferromagnet KCuF3

Phononic and magnetic excitations in the quasi-one-dimensional Heisenberg antiferromagnet KCuF3

Polar phonons and spin-phonon coupling inHgCr2S4andCdC

Magnetodielectric and magnetoelastic coupling in Co4Nb2O9 below Néel temperature

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