Dimensional crossover in a layered ferromagnet detected by spin correlation driven distortions

Abstract

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 3 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 3 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.

Direct observation of the energy gain underpinning ferromagnetic superexchange in the electronic structure of CrGeTe3

“…4(f)]. This suggests that the probability of dd hopping processes scales with the spin-spin correlation length, which will be gradually suppressed with increasing temperature above T C where short-range spin fluctuations are known to persist [40][41][42].…”

Evidence for an extended critical fluctuation region above the polar ordering transition in LiOsO3

“…Previous work has shown that χ ED i jk is linearly proportional to the polar order parameter and dominates the low-temperature SHG response from LiOsO 3 [8]. However, in the centrosymmetric state above T c , a finite SHG response can still arise from higher-multipole radiation, such as via an electric quadrupole (EQ) process P i (2ω) = χ EQ i jkl E j (ω)∇ k E l (ω), which is highly sensitive to symmetry-preserving lattice distortions [21], or a magnetic dipole process, which can be ruled out in our case (see Appendix C). To detect and isolate the EQ from the ED contribution in LiOsO 3 , we performed angle-of-incidence dependent SHG measurements in the S in -S out geometry.…”

Mirror symmetry breaking in a model insulating cuprate

“…The quasi-linear intensity increase in the P-output channels observed upon cooling [Fig. 3 inset] can be attributed to non-uniform changes in the crystallographic χ EQ(i) elements [25]. This likely arises from the anisotropic thermal contraction of the Sr 2 CuO 2 Cl 2 lattice.…”