8 research outputs found
Dimensional crossover in a layered ferromagnet detected by spin correlation driven distortions
Magneto-elastic distortions are commonly detected across magnetic long-range
ordering (LRO) transitions. In principle, they are also induced by the magnetic
short-range ordering (SRO) that precedes a LRO transition, which contains
information about short-range correlations and energetics that are essential
for understanding how LRO is established. However these distortions are
difficult to resolve because the associated atomic displacements are
exceedingly small and do not break symmetry. Here we demonstrate high-multipole
nonlinear optical polarimetry as a sensitive and mode selective probe of SRO
induced distortions using CrSiTe as a testbed. This compound is composed of
weakly bonded sheets of nearly isotropic ferromagnetically interacting spins
that, in the Heisenberg limit, would individually be impeded from LRO by the
Mermin-Wagner theorem. Our results show that CrSiTe evades this law via a
two-step crossover from two- to three-dimensional magnetic SRO, manifested
through two successive and previously undetected totally symmetric distortions
above its Curie temperature.Comment: 17 pages main text, 4 figures, 12 pages supplementary informatio
Ultrafast Enhancement of Ferromagnetic Spin Exchange Induced by Ligand-to-Metal Charge Transfer
We theoretically predict and experimentally demonstrate a nonthermal pathway to optically enhance superexchange interaction energies in a material based on exciting ligand-to-metal charge-transfer transitions, which introduces lower-order virtual hopping contributions that are absent in the ground state. We demonstrate this effect in the layered ferromagnetic insulator CrSiTe₃ by exciting Te-to-Cr charge-transfer transitions using ultrashort laser pulses and detecting coherent phonon oscillations that are impulsively generated by superexchange enhancement via magneto-elastic coupling. This mechanism kicks in below the temperature scale where short-range in-plane spin correlations begin to develop and disappears when the excitation energy is tuned away from the charge-transfer resonance, consistent with our predictions
Ultrafast Enhancement of Ferromagnetic Spin Exchange Induced by Ligand-to-Metal Charge Transfer
We theoretically predict and experimentally demonstrate a nonthermal pathway to optically enhance superexchange interaction energies in a material based on exciting ligand-to-metal charge-transfer transitions, which introduces lower-order virtual hopping contributions that are absent in the ground state. We demonstrate this effect in the layered ferromagnetic insulator CrSiTe₃ by exciting Te-to-Cr charge-transfer transitions using ultrashort laser pulses and detecting coherent phonon oscillations that are impulsively generated by superexchange enhancement via magneto-elastic coupling. This mechanism kicks in below the temperature scale where short-range in-plane spin correlations begin to develop and disappears when the excitation energy is tuned away from the charge-transfer resonance, consistent with our predictions