Magnetism and anomalous apparently inverse Jahn-Teller effect in Sr₂CrO₄

Abstract

We have performed neutron diffraction measurements of tetragonal Sr2CrO4 to study the crystallographic structure as a function of temperature and the magnetic properties developed below . We have measured the precise positions of the oxygen atoms of the CrO6 octahedra and observed that, with decreasing temperature, the octahedra pass from elongated to almost ideal, contradicting the intuitive idea of a Jahn-Teller effect. DFT calculations explain this apparent anomalous behaviour by establishing that energy level degeneracy only exists in a highly elongated octahedra. Our study agrees with the idea of a weak orbital ordering transition around 150 K followed by an itinerant antiferromagnetic ordering at 110 K with a wave vector determined both from neutron powder diffraction and theory.

Ultrafast signatures of spin and orbital order in antiferromagnetic $α$-Sr$_2$CrO$_4$

“…This is supported by the fact that the c-axis lattice constant in the CrO 6 octahedral structure decreases below T O , as shown in Fig. S6 [9,25]. Such distortions in the octahedral structure can change the hybridization strength between t 2g and e g orbitals [30], which in turn affects the on-site relaxation of photoinduced carriers from e g states to t 2g states after 3.1 eV photoexcitation (Fig.…”

“…The case of α-Sr 2 CrO 4 is particularly interesting, as it has been shown to exhibit multiple spin and orbital ordering transitions in the Mott insulating ground state (Fig. 1(a)) [8][9][10][11][12]. α-Sr 2 CrO 4 presents a unique electronic configuration, with two electrons in t 2g orbitals and total spin of S = 1.…”

“…To observe non-equilibrium spin and orbital ordering dynamics, we used our 1.0 eV and 3.1 eV pump pulses to drive specific transitions in the electronic structure of α-Sr 2 CrO 4 . Two electrons occupy Cr 4+ t 2g states in α-Sr 2 CrO 4 , leading to a reversed crystal splitting effect that lifts their degeneracy [9,15]. This results in a lower energy for the d xy orbital compared to those of the d yz /d zx orbitals (Fig.…”

Ultrafast signatures of spin and orbital order in antiferromagnetic α-Sr2CrO4

“…The case of α-Sr 2 CrO 4 is particularly interesting, as it has been shown to exhibit multiple spin and orbital ordering transitions in the Mott insulating ground state (Fig. 1(a)) [8][9][10][11][12]. α-Sr 2 CrO 4 presents a unique electronic configuration, with two electrons in t 2g orbitals and total spin of S = 1.…”

“…α-Sr 2 CrO 4 presents a unique electronic configuration, with two electrons in t 2g orbitals and total spin of S = 1. Recent resonant X-ray scattering (RXS) [8] and neutron powder diffraction studies [9] demonstrated antiferromagnetic (AFM) order by tracking a magnetic Bragg peak below the Néel temperature (T N = 112 K), consistent with the temperature (T )-dependent magnetic susceptibility [10]. The RXS study also revealed another in-plane order below T S = 50 K [8], which was attributed to stripe-type spin-orbital order in the d yz /d zx orbital sub-manifold (Fig.…”