Optical spectroscopy of charge transfer transitions in multiferroic manganites, ferrites, and related insulators (Review Article)

We review results of theoretical and experimental studies of charge transfer (CT) transitions in multiferroic manganites, ferrites, and related insulators. Starting with a simple cluster model approach we address both onecenter p–d and two-center d–d CT transitions, their polarization properties, the role played by structural parameters, orbital mixing, and spin degree of freedom. We analyze optical ellipsometry data in the spectral range of 0.6–5.8 eV in perovskite and hexagonal rare-earth manganites RMnO₃ and in orthorhombic manganites RMn₂O₅. We discuss two groups of iron oxides where Fe³⁺ ions occupy either only octahedral positions (BiFeO₃, orhoferrites RFeO₃ et al.) and materials with Fe³⁺ ions both in octahedral and tetrahedral positions (hematite α-Fe₂O₃, garnets RFe₅O₁₂, lithium ferrite LiFe₅O₈, Ca₂Fe₂O₅ et al.)

Terahertz emission spectroscopy of laser-induced spin dynamics in TmFeO3 and ErFeO3 orthoferrites

Copyright © 2014 American Physical SocietyUsing the examples of laser-induced spin-reorientation phase transitions in TmFeO3 and ErFeO3 orthoferrites, we demonstrate that terahertz emission spectroscopy can obtain novel information about ultrafast laser-induced spin dynamics, which is not accessible by more common all-optical methods. The power of the method is evidenced by the fact that, in addition to the expected quasi-ferromagnetic and quasi-antiferromagnetic modes of the iron sublattices, terahertz emission spectroscopy enables detection of a resonance optically excited at an unexpected frequency of ∼0.3–0.35 THz. By recording how the amplitude and phase of the excited oscillations depend on temperature and applied magnetic field, we show that the unexpected mode has all the features of a spin resonance of the Fe3+ ions. We suggest that it can be assigned to transitions between the multiplet sublevels of the 6A1 ground state of the Fe+3 ions occupying rare-earth positions.European Commission's 7th Framework Program (FP7/2007–2013)Engineering and Physical Sciences Research Council (EPSRC)Netherlands Organization for Scientific Research (NWO)Foundation for Fundamental Research on Matter (FOM)ERCRussian GovernmentRFB

Nonlinear optical spectroscopy of epitaxial magnetic garnet films

Second and third harmonic optical spectra are studied in epitaxial magnetic thin films in the spectral ranges 1.7-3.2 eV and 2.4-4.2 eV, respectively. No significant increase of the intensity of the nonlinear spectra is found above the bandgap near 3.2 eV, where the linear absorption increases by two orders of magnitude. Large magnetic contributions to the second harmonic spectra and magnetic contrast as high as 100% are observed at selected photon energies. Contrary to that, no magnetic contribution to the third harmonic spectra is found

Selective Excitation of Terahertz Magnetic and Electric Dipoles in Er3+ Ions by Femtosecond Laser Pulses in ErFeO3

We show that femtosecond laser pulse excitation of the orthoferrite ErFeO3 triggers pico- and subpicosecond dynamics of magnetic and electric dipoles associated with the low energy electronic states of the Er3+ ions. These dynamics are readily revealed by using polarization sensitive terahertz emission spectroscopy. It is shown that by changing the polarization of the femtosecond laser pulse one can excite either electric dipole-active or magnetic dipole-active transitions between the Kramers doublets of the 4I15/2 ground state of the Er3+(4f11) ions. These observations serve as a proof of principle of polarization-selective control of both electric and magnetic degrees of freedom at terahertz frequencies, opening up new vistas for optical manipulation of magnetoelectric materials

Ultrafast all-optical control of the magnetization in magnetic dielectrics

The purpose of this review is to summarize the recent progress on laser-induced magnetization dynamics in magnetic dielectrics. Due to the slow phonon–magnon interaction in these materials, direct thermal effects of the laser excitation can only be seen on the time scale of almost a nanosecond and thus are clearly distinguished from the ultrafast nonthermal effects. However, via the crystal field, laser pulses are shown to indirectly modify the magnetic anisotropy in rare-earth orthoferrites and lead to the spin reorientation within a few picoseconds. More interesting, however, are the direct nonthermal effects of light on spin systems. We demonstrate coherent optical control of the magnetization in ferrimagnetic garnet films on a femtosecond time scale through a combination of two different ultrafast and nonthermal photomagnetic effects and by employing multiple pump pulses. Linearly polarized laser pulses are shown to create a long-lived modification of the magnetocrystalline anisotropy via optically induced electron transfer between nonequivalent ion sites. In addition, circularly polarized pulses are shown to act as strong transient magnetic field pulses originating from the nonabsorptive inverse Faraday effect. An all-optical scheme of excitation and detection of different antiferromagnetic resonance modes with frequencies of up to 500 GHz will be discussed as well. The reported effects open new and exciting possibilities for ultrafast manipulation of spins by light, and provide new insight into the physics of magnetism on ultrafast time scales

Ultrafast optical modification of exchange interactions in iron oxides

Ultrafast non-thermal manipulation of magnetization by light relies on either indirect coupling of the electric field component of the light with spins via spin-orbit interaction or direct coupling between the magnetic field component and spins. Here we propose a scenario for coupling between the electric field of light and spins via optical modification of the exchange interaction, one of the strongest quantum effects with strength of 10(3) Tesla. We demonstrate that this isotropic opto-magnetic effect, which can be called inverse magneto-refraction, is allowed in a material of any symmetry. Its existence is corroborated by the experimental observation of terahertz emission by spin resonances optically excited in a broad class of iron oxides with a canted spin configuration. From its strength we estimate that a sub-picosecond modification of the exchange interaction by laser pulses with fluence of about 1 mJ cm(-2) acts as a pulsed effective magnetic field of 0.01 Tesla.European Commission’s 7th Framework Program (FP7/2007–2013)EPSRCNetherlands Organization for Scientific Research (NWO)Foundation for Fundamental Research on Matter (FOM)European Research CouncilRussian Ministry of Education and ScienceRFBR-NSFC projectBureau of International CooperationNSFC projectNSFC-NWOEU Seventh Framework ProgramNWO by a Rubicon grantEuropean Commission (FP7-ICT-2013-613024–GRASP

Ultrafast quenching of the antiferromagnetic order in FeBO3: Direct optical probing of the phonon-magnon coupling

Contains fulltext : 92619.pdf (publisher's version ) (Open Access

A spectroscopic study of the nonlinear magneto-optical response of garnets

Contains fulltext : 27937___.PDF (publisher's version ) (Open Access

Charge transfer transitions in multiferroic BiFeO3 and related ferrite insulators

Contains fulltext : 75294.pdf (publisher's version ) (Open Access)16 p