Abstract
We have determined the magnetic ground state of the half-metal CrO2 based on 1s2p Resonant Inelastic X-ray Scattering Magnetic Circular Dichroism (RIXS-MCD) experiments. The two-dimensional RIXS-MCD map displays the 1s X-ray absorption spectrum combined with the 1s2p X-ray emission decay, where there is a large MCD contrast in the final state involving the 2p core hole.Our measurements show that the Cr K pre-edge structure is dominated by dipolar contributions and the quadrupole peak is invisible in direct K pre-edge absorption. Using RIXS-MCD, we reveal that the quadrupole 1s3d pre-edge has a large MCD contrast, which appears at lower energy with respect to the K pre-edge maximum.We use crystal field multiplet calculations to model the excitonic RIXS-MCD spectral shape in tetragonal (D4h) symmetry. The RIXS-MCD is strongly sensitive to the ground state distortion of the Cr4+ sites. The calculations of the RIXS-MCD maps suggest that the 3d spin–orbit interaction is fully quenched (ζ3d=0meV) and the ground state electron configuration must contain a 3B2g (D4h) contribution, which is required to explain the appearance of the Magnetic Circular Dichroism (MCD) in the Cr K pre-edge. This is in apparent contrast with the compressed tetragonal distortion.
Highlights
The detection of the X-ray magnetic circular dichroism (XMCD) has become a powerful tool for the element-specific study of the magnetic properties of complex systems
Some of the above limitations can be addressed with the novel RIXS-Magnetic Circular Dichroism (MCD) approach, in which one combines XMCD and resonant inelastic X-ray scattering (RIXS) at the K pre-edge of 3d transition metals according to the following two-step-model (Fig. 1)
Even though a 3B2g (D4h) ground state appears to contradict the requirements for the proposed double-exchange mechanism as cited above [30,46], and it is known that the ground state at absolute zero temperature should be a 3Eg (D4h) ground state, our calculations show that we find multiple solutions yielding a RIXS-MCD map comparable to the experimental data for 3B2g (D4h) ground states
Summary
The detection of the X-ray magnetic circular dichroism (XMCD) has become a powerful tool for the element-specific study of the magnetic properties of complex systems. The MCD of 3d transition metal ions is usually studied at the spin–orbit split L2,3 absorption edges (2p → 3d) to allow the determination of the spin and orbital magnetic moments using the sum rules [15,44]. The L2,3-edges of 3d transition metals are in the soft X-ray range requiring vacuum conditions, implying that they are difficult for liquid or high-pressure cells. This limits the number of possible applications and the nature of the samples. Edge of 3d transition metals lies in the hard X-ray range, but the direct K-edge MCD signal is weak and the absence of spin–orbit splitting a priori prohibits a quantitative analysis using the spin sum rules. Some of the above limitations can be addressed with the novel RIXS-MCD approach, in which one combines XMCD and resonant inelastic X-ray scattering (RIXS) at the K pre-edge of 3d transition metals according to the following two-step-model (Fig. 1)
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