Microscopic Origin of Heisenberg and Non-Heisenberg Exchange Interactions in Ferromagnetic bcc Fe

At the present time two models can more or less describe the magnetic properties ofNi4Mo12. The rst one is based on the assumption of essential role of non-Heisenberg exchangeinteractions. The key feature of the second model is the symmetry breaking of exchange inter-actions. The present work is focused on the forecasting power of these spin models. Mechanismresponsible for non-Heisenberg exchange interactions is the same as mechanism resulting in in-teraction of spin chirality with external magnetic eld. An additional level splitting in magnetic eld can be observed in this case. The symmetry breaking of exchange interactions inevitablyleads to nonzero toroidal moment and related to it magnetoelectric phenomena.

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Environmental screening and ligand-field effects to magnetism in CrI3 monolayer

npj Computational Materials ◽

10.1038/s41524-021-00631-4 ◽

2021 ◽

Vol 7 (1) ◽

Author(s):

D. Soriano ◽

A. N. Rudenko ◽

M. I. Katsnelson ◽

M. Rösner

Keyword(s):

Ab Initio Calculations ◽

Ab Initio ◽

Nearest Neighbor ◽

Hexagonal Boron Nitride ◽

Magnetic Moments ◽

Random Phase ◽

Exchange Interactions ◽

Ligand Field ◽

Hubbard Models ◽

Microscopic Origin

AbstractWe study the microscopic origin of magnetism in suspended and dielectrically embedded CrI3 monolayer by down-folding minimal generalized Hubbard models from ab initio calculations using the constrained random phase approximation. These models are capable of describing the formation of localized magnetic moments in CrI3 and of reproducing electronic properties of direct ab initio calculations. Utilizing the magnet force theorem, we find a multi-orbital super-exchange mechanism as the origin of magnetism in CrI3 resulting from an interplay between ferro- and anti-ferromagnetic Cr-Cr d coupling channels, which is decisively affected by the ligand p orbitals. We show how environmental screening, such as resulting from encapsulation with hexagonal boron nitride, affects the Coulomb interaction in the film and how this controls its magnetic properties. Driven by a non-monotonic interplay between nearest and next-nearest neighbor exchange interactions we find the magnon dispersion and the Curie temperature to be non-trivially affected by the environmental screening.

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Exchange interactions and the nature of magnetic ordering in Zn0.6Mn2.4O4 particles

Physica B Condensed Matter ◽

10.1016/j.physb.2020.412460 ◽

2020 ◽

Vol 599 ◽

pp. 412460

Author(s):

N. Rajeesh Kumar ◽

R. Kalai Selvan ◽

Leonid Vasylechko ◽

P. Saravanan ◽

Mohindar S. Seehra

Keyword(s):

Magnetic Ordering ◽

Exchange Interactions

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The Domain and Microstructure of Resin-Bonded Magnets

Materials ◽

10.3390/ma14112849 ◽

2021 ◽

Vol 14 (11) ◽

pp. 2849

Author(s):

Marcin Jan Dośpiał

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Grain Size ◽

Size Distribution ◽

Domain Structure ◽

Grain Size Distribution ◽

Exchange Interactions ◽

Force Microscopy ◽

Transmission Electron ◽

Scanning Electron

This paper presents domain and structure studies of bonded magnets made from nanocrystalline Nd-(Fe, Co)-B powder. The structure studies were investigated using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Mössbauer spectroscopy and X-ray diffractometry. On the basis of performed qualitative and quantitative phase composition studies, it was found that investigated alloy was mainly composed of Nd2(Fe-Co)14B hard magnetic phase (98 vol%) and a small amount of Nd1.1Fe4B4 paramagnetic phase (2 vol%). The best fit of grain size distribution was achieved for the lognormal function. The mean grain size determined from transmission electron microscopy (TEM) images on the basis of grain size distribution and diffraction pattern using the Bragg equation was about ≈130 nm. HRTEM images showed that over-stoichiometric Nd was mainly distributed on the grain boundaries as a thin amorphous border of 2 nm in width. The domain structure was investigated using a scanning electron microscope and metallographic light microscope, respectively, by Bitter and Kerr methods, and by magnetic force microscopy. Domain structure studies revealed that the observed domain structure had a labyrinth shape, which is typically observed in magnets, where strong exchange interactions between grains are present. The analysis of the domain structure in different states of magnetization revealed the dynamics of the reversal magnetization process.

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