Magnetic-field-controlled multitude of spin excitation modes in magnetoelectric 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Co</mml:mi><mml:mn>4</mml:mn></mml:msub><mml:msub><mml:mi>Nb</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>9</mml:mn></mml:msub></mml:mrow></mml:math>
 as investigated by magnetoterahertz spectroscopy

Dagar, Rahul; Yadav, Satish; Kinha, Monu; Mehra, Brijesh Singh; Rawat, R.; Singh, Kiran; Rana, D. S.

doi:10.1103/physrevmaterials.6.074409

Cited by 5 publications

(1 citation statement)

References 52 publications

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“…THz time-domain spectroscopic measurements were performed by a fiber-coupled Tera K15 spectrometer (Menlo Systems) equipped with a closed-cycle helium cryostat (Oxford). Detailed information about THz-TDS spectroscopy is provided elsewhere [29]. Various optical constants, such as THz conductivity, dielectric constant, etc., were extracted experimentally using the following methodology: first, for a fixed temperature, the THz waveform is passed through free space (vacuum) and is recorded.…”

Section: Methodsmentioning

confidence: 99%

Observation of negative terahertz photoconductivity in strongly correlated electron-doped CaMnO₃ thin film

Kinha

Dagar

Sahoo

et al. 2023

J. Phys.: Condens. Matter

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Electron-doped Ca0.96Ce0.04MnO3 (CCMO) possesses a unique band structure and exhibits a giant topological Hall effect contrary to other correlation-driven manganites known for insulator-to-metal transition, magnetoresistance, complex magnetic order, etc. The interaction mechanisms among the fundamental entities and their dynamical evolutions responsible for this unusual topological phase are yet to be understood. Here, we employ time-averaged and sub-picosecond time-resolved terahertz (THz) spectroscopy to explore the low-energy steady-state and ultrafast carrier dynamics, respectively, to unravel the complexity of charge carriers during their transition from a non-equilibrium to the ground state in CCMO thin film. The THz optical conductivity confirms the presence of dichotomic charge carriers, i.e., heavy and light carriers throughout the temperature range of 15-300 K. A rare observation of both positive and negative photoconductivities along with a sharp crossover between the two resolved to a few picoseconds of illumination confirms the formation of polaron with a lifetime of a few nanoseconds. These optical evidences of dichotomic charge carriers, along with manipulation of the sign of photoconductivity induced by dynamics of related quasiparticles could facilitate a new mechanism for ultrafast optoelectronic switching devices.

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Section: Methodsmentioning

confidence: 99%

Observation of negative terahertz photoconductivity in strongly correlated electron-doped CaMnO₃ thin film

Kinha

Dagar

Sahoo

et al. 2023

J. Phys.: Condens. Matter

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Terahertz Crystal-Field Transitions and Quasi Ferromagnetic Magnon Excitations in a Noncollinear Magnet for Hybrid Spin-Wave Computation

Dubey,

Mehra,

Kumar

et al. 2024

ACS Appl. Mater. Interfaces

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The complexity of interactions between the crystal-field and unusual noncollinear spin arrangement in nontrivial magnets demands novel tools to unravel the mystery underneath. In this work, we study such interaction dynamics of crystal-field excitations (CFE) and low-energy magnetic excitations in orthochromite TmCrO 3 with controls of temperature and magnetic field using high-resolution magneto-terahertz (THz) time-domain spectroscopy. The THz energy spectrum spanning 0.5−10 meV possesses a low-frequency spin-excitation (magnon) mode and a multitude of CFE modes at 10 K, all of which uniquely embody a range of phenomena. For the magnon mode, a temperature dependence of peak frequency is induced by magnetic interactions between Tm and Cr subsystems. While a change from blue to red shift of peak frequency of this mode marks the magnetization reversal transition, the spin-reorientation temperature and change of magnetic anisotropy are depicted by different features of field and temperature dependent peak frequency dynamics. The modes corresponding to CFE are robust and laden with a multitude of submodes, which are attributes of nontrivial interactions across different transitions. These modes are suppressed only upon substitution of Tb 3+ at the Tm 3+ site, which suggests a dominant role of single-ion anisotropy in controlling entire THz excitation spectra. Overall, this remarkable range of phenomena seen through the unique lens of all-optical THz tools provides deeper insights into the origin of magnetic phases in systems with complex interactions between rare-earth and transition metal ions and provides a multitude of novel combinations of closely spaced modes for emerging hybrid spin-wave computation.

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Spin–phonon interactions and magnetoelectric coupling in Co4B2O9 (B = Nb, Ta)

Park

Kim

Choi

et al. 2023

Applied Physics Letters

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In order to explore the consequences of spin–orbit coupling on spin–phonon interactions in a set of chemically similar mixed metal oxides, we measured the infrared vibrational properties of Co4B2O9 (B = Nb, Ta) as a function of temperature and compared our findings with lattice dynamics calculations and several different models of spin–phonon coupling. Frequency vs temperature trends for the Co2+ shearing mode near 150 cm−1 reveal significant shifts across the magnetic ordering temperature that are especially large in relative terms. Bringing these results together and accounting for noncollinearity, we obtain spin–phonon coupling constants of −3.4 and −4.3 cm−1 for Co4Nb2O9 and the Ta analog, respectively. Analysis reveals that these coupling constants are derived from interlayer (rather than intralayer) exchange interactions and that the interlayer interactions contain competing antiferromagnetic and ferromagnetic contributions. At the same time, beyond-Heisenberg terms are minimized due to fortuitous symmetry considerations, different from most other 4d- and 5d-containing oxides. Comparison with other contemporary oxides shows that spin–phonon coupling in this family of materials is among the strongest ever reported, suggesting an origin for magnetoelectric coupling.

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Magnetic-field-controlled multitude of spin excitation modes in magnetoelectric Co4Nb2O9 as investigated by magnetoterahertz spectroscopy

Cited by 5 publications

References 52 publications

Observation of negative terahertz photoconductivity in strongly correlated electron-doped CaMnO₃ thin film

Observation of negative terahertz photoconductivity in strongly correlated electron-doped CaMnO₃ thin film

Terahertz Crystal-Field Transitions and Quasi Ferromagnetic Magnon Excitations in a Noncollinear Magnet for Hybrid Spin-Wave Computation

Spin–phonon interactions and magnetoelectric coupling in Co4B2O9 (B = Nb, Ta)

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Magnetic-field-controlled multitude of spin excitation modes in magnetoelectric Co4Nb2O9 as investigated by magnetoterahertz spectroscopy

Cited by 5 publications

References 52 publications

Observation of negative terahertz photoconductivity in strongly correlated electron-doped CaMnO3 thin film

Observation of negative terahertz photoconductivity in strongly correlated electron-doped CaMnO3 thin film

Terahertz Crystal-Field Transitions and Quasi Ferromagnetic Magnon Excitations in a Noncollinear Magnet for Hybrid Spin-Wave Computation

Spin–phonon interactions and magnetoelectric coupling in Co4B2O9 (B = Nb, Ta)

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Observation of negative terahertz photoconductivity in strongly correlated electron-doped CaMnO₃ thin film

Observation of negative terahertz photoconductivity in strongly correlated electron-doped CaMnO₃ thin film