Publication

Magnetic exchange parameters and anisotropy of the quasi-two-dimensional antiferromagnet NiPS3

Résumé

Neutron inelastic scattering has been used to measure the magnetic excitations in powdered NiPS3, a quasitwo-dimensional antiferromagnet with spin S = 1 on a honeycomb lattice. The spectra show clear, dispersive magnons with a similar to 7 meV gap at the Brillouin zone center. The data were fitted using a Heisenberg Hamiltonian with a single-ion anisotropy assuming no magnetic exchange between the honeycomb planes. Magnetic exchange interactions up to the third intraplanar nearest neighbor were required. The fits show robustly that NiPS 3 has an easy-axis anisotropy with Delta = 0.3 meV and that the third nearest neighbor has a strong antiferromagnetic exchange of J(3) = -6.90 meV. The data can be fitted reasonably well with either J(1) < 0 or J(1) > 0, however, the best quantitative agreement with high-resolution data indicates that the nearest-neighbor interaction is ferromagnetic with J(1) = 1.9 meV and that the second nearest-neighbor exchange is small and antiferromagnetic with J(2) = -0.1 meV. The dispersion has a minimum in the Brillouin zone corner that is slightly larger than that at the Brillouin zone center, indicating that the magnetic structure of NiPS3 is close to being unstable.

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Concepts associés (32)
Anisotropie magnétique
Une anisotropie magnétique est présente lorsque les propriétés magnétiques d'un système sont orientées selon des axes privilégiés. C'est le cas dans les matériaux ferromagnétiques, où l’aimantation suit des directions privilégiées appelées axes de facile aimantation. Dans les matériaux cristallins, il existe des directions selon lesquelles il est facile d'aimanter le cristal (axes faciles), et des directions de difficile aimantation, on parle d'anisotropie magnéto-cristalline.
Magnetic domain
A magnetic domain is a region within a magnetic material in which the magnetization is in a uniform direction. This means that the individual magnetic moments of the atoms are aligned with one another and they point in the same direction. When cooled below a temperature called the Curie temperature, the magnetization of a piece of ferromagnetic material spontaneously divides into many small regions called magnetic domains. The magnetization within each domain points in a uniform direction, but the magnetization of different domains may point in different directions.
Interaction d'échange
En physique, l'interaction d'échange (avec une énergie et un terme d'échange) est un effet en mécanique quantique qui se produit seulement entre particules identiques. L'interaction d'échange modifie la valeur moyenne de la distance entre deux ou plusieurs particules indistinguables lorsque leur fonctions d'onde se chevauchent. A cause de l’interaction d’échange cette distance va augmenter (pour les fermions) ou diminuer (pour les bosons) par rapport au cas où les particules seraient distinguables.
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