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Register a new userAnisotropic spin distribution and perpendicular magnetic anisotropy in the layered ferromagnetic semiconductor (Ba,K)(Zn,Mn)$_{2}$As$_{2}$
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Perpendicular magnetic anisotropy of the new ferromagnetic semiconductor (Ba,K)(Zn,Mn)$_{2}$As$_{2}$ is studied by angle-dependent x-ray magnetic circular dichroism measurements. The large magnetic anisotropy with the anisotropy field of 0.85 T is deduced by fitting the Stoner-Wohlfarth model to the magnetic-field-angle dependence of the projected magnetic moment. Transverse XMCD spectra highlights the anisotropic distribution of Mn 3$d$ electrons, where the $d_{xz}$ and $d_{yz}$ orbitals are less populated than the $d_{xy}$ state because of the $D_{2d}$ splitting arising from the elongated MnAs$_{4}$ tetrahedra. It is suggested that the magnetic anisotropy originates from the degeneracy lifting of $p$-$d_{xz}$, $d_{yz}$ hybridized states at the Fermi level and resulting energy gain due to spin-orbit coupling when spins are aligned along the $z$ direction.
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Heavily doped Ba$_{1-x}$K$_{x}$Mn$_{2}$As$_{2}$ ($x$=0.19 and 0.26) single crystals were successfully grown, and investigated by the measurements of resistivity and anisotropic magnetic susceptibility. In contrast to the antiferromagnetic insulating ground state of the undoped BaMn$_{2}$As$_{2}$, the K-doped crystals show metallic conduction with weak ferromagnetism below $sim$50 K and Curie-Weiss-like in-plane magnetic susceptibility above $sim$50 K. Under high pressures up to 6 GPa, the low-temperature metallicity changes into a state characterized by a Kondo-like resistivity minimum without any signature of superconductivity above 2.5 K. Electronic structure calculations for $x$=0.25 using $2times2times1$ supercell reproduce the hole-doped metallic state. The density of states at Fermi energy have significant As 4$p$ components, suggesting that the 4$p$ holes are mainly responsible for the metallic conduction. Our results suggest that the interplay between itinerant 4$p$ holes and local 3$d$ moments is mostly responsible for the novel metallic state.
X-ray magnetic circular dichroism (XMCD) measurements on single-crystal and powder samples of Ba$_{0.6}$K$_{0.4}$Mn$_{2}$As$_{2}$ show that the ferromagnetism below $T_{textrm{C}}approx$ 100 K arises in the As $4p$ conduction band. No XMCD signal is observed at the Mn x-ray absorption edges. Below $T_{textrm{C}}$, however, a clear XMCD signal is found at the As $K$ edge which increases with decreasing temperature. The XMCD signal is absent in data taken with the beam directed parallel to the crystallographic $textrm{c}$ axis indicating that the orbital magnetic moment lies in the basal plane of the tetragonal lattice. These results show that the previously reported itinerant ferromagnetism is associated with the As $4p$ conduction band and that distinct local-moment antiferromagnetism and itinerant ferromagnetism with perpendicular easy axes coexist in this compound at low temperature.
We investigated the static and dynamic magnetic properties of the polar ferrimagnet Mn$_2$Mo$_3$O$_8$ in three magnetically ordered phases via magnetization, magnetic torque, and THz absorption spectroscopy measurements. The observed magnetic field dependence of the spin-wave resonances, including Brillouin zone-center and zone-boundary excitations, magnetization, and torque, are well described by an extended two-sublattice antiferromagnetic classical mean-field model. In this orbitally quenched system, the competing weak easy-plane and easy-axis single-ion anisotropies of the two crystallographic sites are determined from the model and assigned to the tetra- and octahedral sites, respectively, by ab initio calculations.
The electronic and magnetic properties of a new diluted magnetic semiconductor (DMS) Ba$_{1-x}$K$_{x}$(Zn$_{1-y}$Mn$_{y}$)$_{2}$As$_{2}$, which is isostructural to so-called 122-type Fe-based superconductors, are investigated by x-ray absorption spectroscopy (XAS) and resonance photoemission spectroscopy (RPES). Mn $L_{2,3}$-edge XAS indicates that the doped Mn atoms have the valence 2+ and strongly hybridize with the $4p$ orbitals of the tetrahedrally coordinating As ligands. The Mn $3d$ partial density of states (PDOS) obtained by RPES shows a peak around 4 eV and relatively high between 0-2 eV below the Fermi level ($E_{F}$) with little contribution at $E_{F}$, similar to that of the archetypal DMS Ga$_{1-x}$Mn$_{x}$As. This energy level creates $d^{5}$ electron configuration with $S=5/2$ local magnetic moments at the Mn atoms. Hole carriers induced by K substitution for Ba atoms go into the top of the As $4p$ valence band and are weakly bound to the Mn local spins. The ferromagnetic correlation between the local spins mediated by the hole carriers induces ferromagnetism in Ba$_{1-x}$K$_{x}$(Zn$_{1-y}$Mn$_{y}$)$_{2}$As$_{2}$
We use polarized inelastic neutron scattering to study the temperature and energy dependence of spin space anisotropies in the optimally hole-doped iron pnictide Ba$_{0.67}$K$_{0.33}$Fe$_{2}$As$_{2}$ ($T_{{rm c}}=38$ K). In the superconducting state, while the high-energy part of the magnetic spectrum is nearly isotropic, the low-energy part displays a pronouced anisotropy, manifested by a $c$-axis polarized resonance. We also observe that the spin anisotropy in superconducting Ba$_{0.67}$K$_{0.33}$Fe$_{2}$As$_{2}$ extends to higher energies compared to electron-doped BaFe$_{2-x}TM_{x}$As$_{2}$ ($TM=$Co, Ni) and isovalent-doped BaFe$_{2}$As$_{1.4}$P$_{0.6}$, suggesting a connection between $T_{rm c}$ and the energy scale of the spin anisotropy. In the normal state, the low-energy spin anisotropy for optimally hole- and electron-doped iron pnictides onset at temperatures similar to the temperatures at which the elastoresistance deviate from Curie-Weiss behavior, pointing to a possible connection between the two phenomena. Our results highlight the relevance of the spin-orbit coupling to the superconductivity of the iron pnictides.
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