The Breit-Pauli and Boson-Exchange Interactions

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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A new 1-1-4 pattern of magnetic exchange interactions in a cubane core tetranuclear copper (II) complex

Polyhedron ◽

10.1016/j.poly.2021.115088 ◽

2021 ◽

Vol 199 ◽

pp. 115088

Author(s):

Azadeh Mehrani ◽

Maurice G. Sorolla ◽

Tatyana Makarenko ◽

Allan J. Jacobson

Keyword(s):

Exchange Interactions ◽

Magnetic Exchange

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Isotropic Nature of the Metallic Kagome Ferromagnet Fe3Sn2 at High Temperatures

Crystals ◽

10.3390/cryst11030307 ◽

2021 ◽

Vol 11 (3) ◽

pp. 307

Author(s):

Rebecca L. Dally ◽

Daniel Phelan ◽

Nicholas Bishop ◽

Nirmal J. Ghimire ◽

Jeffrey W. Lynn

Keyword(s):

Elevated Temperatures ◽

Magnetocrystalline Anisotropy ◽

Inelastic Neutron Scattering ◽

Exchange Interactions ◽

Inelastic Neutron ◽

Temperature Threshold ◽

Magnetic Exchange ◽

Spatial Anisotropy ◽

Isotropic Exchange ◽

State Spin

Anisotropy and competing exchange interactions have emerged as two central ingredients needed for centrosymmetric materials to exhibit topological spin textures. Fe3Sn2 is thought to have these ingredients as well, as it has recently been discovered to host room temperature skyrmionic bubbles with an accompanying topological Hall effect. We present small-angle inelastic neutron scattering measurements that unambiguously show that Fe3Sn2 is an isotropic ferromagnet below TC≈660 K to at least 480 K—the lower temperature threshold of our experimental configuration. Fe3Sn2 is known to have competing magnetic exchange interactions, correlated electron behavior, weak magnetocrystalline anisotropy, and lattice (spatial) anisotropy; all of these features are thought to play a role in stabilizing skyrmions in centrosymmetric systems. Our results reveal that at the elevated temperatures measured, there is an absence of significant magnetocrystalline anisotropy and that the system behaves as a nearly ideal isotropic exchange interaction ferromagnet, with a spin stiffness D(T=480 K)=168 meV Å2, which extrapolates to a ground state spin stiffness D(T=0 K)=231 meV Å2.

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