Element-resolved magnetism across the temperature- and pressure-induced spin reorientation in MnBi

Abstract

Rare-earth free permanent magnet MnBi (NiAs-type crystal structure) displays strong uniaxial magnetic anisotropy above its ∼90 K spin reorientation transition (SRT). X-ray magnetic circular dichroism (XMCD) measurements at the Mn K and Bi L2,3 edges show induced magnetism in Bi, which is strongly coupled to the magnetism of Mn. Temperature-and pressure-dependent XMCD results reveal that hydrostatic pressure mimics the effect of temperature, driving a transition from uniaxial to in-plane anisotropy. The pressure and temperature transitions are shown to be connected to an anisotropic lattice contraction in NiAs-type structures. Temperature and pressure, hence, induce coupled structural and magnetic responses, highlighting the importance of both anisotropic lattice change and Mn-Bi hybridization in leading to the magnetic anisotropy change across the SRT. The dependence of magnetic anisotropy on the anisotropic lattice change is confirmed by density functional theory.

Large linear non-saturating magnetoresistance and high mobility in ferromagnetic MnBi

“…Bi and several of its alloys and compounds, such as Bi–Sb 30 , LaBi 31 , GdPtBi 32 , and Bi 2 Te 3 33 , are topological materials with high mobility, owing to the highly delocalized 6 p electrons of Bi and its high spin–orbital coupling. In MnBi, the Bi 6 p orbital is strongly hybridized with Mn 3 d electrons, confirmed by the induced magnetism in Bi, as proven using X-ray magnetic circular dichroism 27 . Therefore, the transport properties are dominated by the magnetic Bi 6 p electrons.…”

“…5 , allow for the reduction of backscattering which would only increase the mobility. While the linear crossing is present in other ferromagnetic topological metals, MnBi is “special” in that the Bi 6 p bands contribute to the magnetism 27 in addition to the complementary connection between the electron–hole compensation and the topological bands. The linear crossing leads to a special case of electron–hole compensation that shows to drastically enhances the mobility of magnetic systems.…”

Small core–shell Mn0.5Bi0.5−Bi (⩽3 at%) magnets, the anisotropic growth of crystallite nanoplates, interface-bridging, and tailored magnetic properties

“…An inversion of the anisotropic pairwise exchange interaction between Bi atoms is found to be responsible for the SRT signal [7]. Further, Choi et al [39] used density functional theory (DFT) to account for the anisotropic change of lattice and Mn-Bi hybridization in a coupled transition of a uniaxial to in-plane anisotropy K 1 across the SRT at low temperatures. In general, all such features are strongly dependent on the internal structure of a sample in a due force-field of its anisotropic shape, dimension and surfaces, in terms of its small crystallites.…”

A core–shell magnet Mn70Bi30 grown at seeds in magnetic fields and its impacts on its spin-dynamics, Curie point and other tailored properties

“…Long (110) surfaces in (002) h-plates, as projected in figure 1(h), strictly control the surface spins to rotate slowly at M → M s , as H → ∞. Multiple facets generate the multiple surface states [63,70], at c/a spans (table 1) to cope with the net energy [9,68]. Other details of magnetic properties for the different samples are given in table 2. spin-orbit coupling at Mn-3d 5 − 6p 3 -Bi hybridized orbitals regulates the features.…”