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Register a new userMagnetic circular dichroism of x-ray absorption spectroscopy at rare-earth L2,3 edges in RE2Fe14B compounds (RE = La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu)
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Magnetic circular dichroism (MCD) in the x-ray absorption spectroscopy (XAS) at the L2,3 edges for almost entire series of rare-earth (RE) elements in RE2Fe14B, is studied experimentally and theoretically. By a quantitative comparison of the complicated MCD spectral shapes, we find that (i) the 4f-5d intra-atomic exchange interaction not only induces the spin and orbital polarization of the 5d states, which is vital for the MCD spectra of the electric dipole transition from the 2p core states to the empty 5d conduction band, but also it accompanies a contraction of the radial part of the 5d wave function depending on its spin and orbital state, which results in the enhancement of the 2p-5d dipole matrix element, (ii) there are cases where the spin polarization of the 5d states due to the hybridization with the spin polarized 3d states of surrounding irons plays important roles, and (iii) the electric quadrupole transition from the 2p core states to the magnetic vale! nce 4f states is appreciable at the pre-edge region of the dipole spectrum. Especially, our results evidence that it is important to include the enhancement effect of the dipole matrix element in the correct interpretation of the MCD spectra at the RE L2,3 edges.
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The antiferromagnetic transition is investigated in the rare-earth (R) tritelluride RTe3 family of charge density wave (CDW) compounds via specific heat, magnetization and resistivity measurements. Observation of the opening of a superzone gap in the resistivity of DyTe3 indicates that additional nesting of the reconstructed Fermi surface in the CDW state plays an important role in determining the magnetic structure.
We report a Raman scattering study of six rare earth orthoferrites RFeO3, with R = La, Sm, Eu, Gd, Tb, Dy. The use of extensive polarized Raman scattering of SmFeO3 and first-principles calculations enable the assignment of the observed phonon modes to vibrational symmetries and atomic displacements. The assignment of the spectra and their comparison throughout the whole series allows correlating the phonon modes with the orthorhombic structural distortions of RFeO3 perovskites. In particular, the positions of two specific Ag modes scale linearly with the two FeO6 octahedra tilt angles, allowing the distortion throughout the series. At variance with literature, we find that the two octahedra tilt angles scale differently with the vibration frequencies of their respective Ag modes. This behavior as well as the general relations between the tilt angles, the frequencies of the associated modes and the ionic radii are rationalized in a simple Landau model. The reported Raman spectra and associated phonon-mode assignment provide reference data for structural investigations of the whole series of orthoferrites.
We present a systematic study of the structural and magnetic properties of two branches of the rare earth Tripod Kagome Lattice (TKL) family A$_{2}$RE$_{3}$Sb$_{3}$O$_{14}$ (A = Mg, Zn; RE = Pr, Nd, Gd, Tb, Dy, Ho, Er, Yb; here, we use abbreviation textit{A-RE}, as in textit{MgPr} for Mg$_{2}$Pr$_{3}$Sb$_{3}$O$_{14}$), which complements our previously reported work on textit{MgDy}, textit{MgGd}, and textit{MgEr} cite{TKL}. The present susceptibility ($chi_{dc}$, $chi_{ac}$) and specific heat measurements reveal various magnetic ground states, including the non-magnetic singlet state for textit{MgPr}, textit{ZnPr}; long range orderings (LROs) for textit{MgGd}, textit{ZnGd}, textit{MgNd}, textit{ZnNd}, and textit{MgYb}; a long range magnetic charge ordered state for textit{MgDy}, textit{ZnDy}, and potentially for textit{MgHo}; possible spin glass states for textit{ZnEr}, textit{ZnHo}; the absence of spin ordering down to 80 mK for textit{MgEr}, textit{MgTb}, textit{ZnTb}, and textit{ZnYb} compounds. The ground states observed here bear both similarities as well as striking differences from the states found in the parent pyrochlore systems. In particular, while the TKLs display a greater tendency towards LRO, the lack of LRO in textit{MgHo}, textit{MgTb} and textit{ZnTb} can be viewed from the standpoint of a balance among spin-spin interactions, anisotropies and non-Kramers nature of single ion state. While substituting Zn for Mg changes the chemical pressure, and subtly modifies the interaction energies for compounds with larger RE ions, this substitution introduces structural disorder and modifies the ground states for compounds with smaller RE ions (Ho, Er, Yb).
The lanthanide orthoborates, $Ln$BO$_3$, $Ln$ = Gd, Tb, Dy, Ho, Er, Yb crystallise in a monoclinic structure with the magnetic $Ln^{3+}$ forming an edge-sharing triangular lattice. The triangles are scalene, however all deviations from the ideal equilateral geometry are less than 1.5%. The bulk magnetic properties are studied using magnetic susceptibility, specific heat and isothermal magnetisation measurements. Heat capacity measurements show ordering features at $T leq$ 2 K for $Ln$ = Gd, Tb, Dy, Er. No ordering is observed for YbBO$_3$ at $T geq$ 0.4 K and HoBO$_3$ is proposed to have a non-magnetic singlet state. Isothermal magnetisation measurements indicate isotropic Gd$^{3+}$ spins and strong single-ion anisotropy for the other $Ln^{3+}$. The change in magnetic entropy has been evaluated to determine the magnetocaloric effect in these materials. GdBO$_3$ and DyBO$_3$ are found to be competitive magnetocaloric materials in the liquid helium temperature regime.
We present the crystal structures and magnetic properties of RE3Sb3Mg2O14 (La3Sb3Mg2O14, Pr3Sb3Mg2O14, Sm3Sb3Mg2O14, Eu3Sb3Mg2O14, Tb3Sb3Mg2O14, and Ho3Sb3Mg2O14), a family of novel materials based on a perfect geometry 2D rare earth Kagome lattice. Structure refinements were performed by the Rietveld method using X-ray diffraction data, indicating that the layered compounds are fully structurally ordered. The compounds crystallize in a rhombohedral supercell of the cubic pyrochlore structure, in the space group R-3m. As indicated by magnetic susceptibility measurements, they exhibit predominantly antiferromagnetic interactions between rare earth moments. Except for possibly Pr3Sb3Mg2O14 and Eu3Sb3Mg2O14, none of the compounds show any signs of magnetic ordering above 2 K. This RE3Sb3Mg2O14 family of compounds is similar to that of RE3Sb3Zn2O14, except the series reported here features a fully ordered distribution of cations in both the nonmagnetic antimony and magnesium sites and the magnetic rare earth kagome sites. The compounds appear to be relatively defect-free and are therefore model systems for investigating magnetic frustration on an ideal 2D rare earth Kagome lattice.
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