Discovery of a large unquenched orbital moment in a 2D van der Waals ferromagnet

The existence of the V3+-ion orbital moment in the van der Waals ferromagnet VI3 is still an open issue. The huge magnetocrystalline anisotropy in conjunction with the significantly reduced ordered magnetic moment compared to the spin-only value provides strong but indirect evidence of a large V orbital moment. Despite of that, some experimental and theoretical works still indicate a quenched orbital moment. The size of the orbital moment is related to the symmetry and ground state of VI3, and therefore in order to understand and model this system it is important to solve this open question.

In our work we have used the unique capability of x-ray magnetic circular dichroism to determine the orbital component of the magnetic moment. Our results provide a direct proof of an exceptionally sizable orbital moment of the V3+ ion in VI3. Moreover, we have employed ligand field multiplet simulations of the XMCD spectra. Our simulations where done in synergy with results from DFT calculations. The simulations agree with the existence of two V sites with different orbital occupations and magnitudes of the orbital moment in the ground state. Our results give an important piece of information in the understanding of the exotic properties of this system.

VI3_XMCD
Left: measurement sketch. Right: measured XAS and XMCD plotted together with simulation. The proposed orbital occupation of the two V sites are also shown.

In our work we have used the unique capability of x-ray magnetic circular dichroism to determine the orbital component of the magnetic moment. Our results provide a direct proof of an exceptionally sizable orbital moment of the V3+ ion in VI3. Moreover, we have employed ligand field multiplet simulations of the XMCD spectra. Our simulations where done in synergy with results from DFT calculations. The simulations agree with the existence of two V sites with different orbital occupations with different magnitudes of the orbital moment in the ground state. Our results solve the open debate and give an important piece of information in the understanding of the exotic properties of this system. It also shows that the existence of an unquenched orbital moment can be more general in other 2D van der Waals systems exhibiting high magnetic anisotropy.

Contact

Dr Cinthia Piamonteze
Microscopy and Magnetism Group

Paul Scherrer Institute, Forschungsstrasse 111, 5232 Villigen PSI, Switzerland
Telephone: +41 56 310 58 55
E-mail: cinthia.piamonteze@psi.ch

 
Original Publication

Large Orbital Magnetic Moment in VI3
D. Hovančík,* J.Pospíšil, K. Carva, V. Sechovský, and C. Piamonteze*
Nano Lett. 2023, Published 1 February
DOI: 10.1021/acs.nanolett.2c04045