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Register a new userMagnetic properties of the Ag-In-rare-earth 1/1 approximants
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We have performed magnetic susceptibility and neutron scattering measurements on polycrystalline Ag-In-RE (RE: rare-earth) 1/1 approximants. In the magnetic susceptibility measurements, for most of the RE elements, inverse susceptibility shows linear behaviour in a wide temperature range, confirming well localized isotropic moments for the RE$^{3+}$ ions. Exceptionally for the light RE elements, such as Ce and Pr, non-linear behaviour was observed, possibly due to significant crystalline field splitting or valence fluctuation. For RE = Tb, the susceptibility measurement clearly shows a bifurcation of the field-cooled and zero-field-cooled susceptibility at $T_{rm f} = 3.7$~K, suggesting a spin-glass-like freezing. On the other hand, neutron scattering measurements detect significant development of short-range antiferromagnetic spin correlations in elastic channel, which accompanied by a broad peak at $hbaromega = 4$~meV in inelastic scattering spectrum. These features have striking similarity to those in the Zn-Mg-Tb quasicrystals, suggesting that the short-range spin freezing behaviour is due to local high symmetry clusters commonly seen in both the systems.
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The acute sensitivity of the electrical resistance of certain systems to magnetic fields known as extreme magnetoresistance (XMR) has recently been explored in a new materials context with topological semimetals. Exemplified by WTe$_{2}$ and rare earth monopnictide La(Sb,Bi), these systems tend to be non-magnetic, nearly compensated semimetals and represent a platform for large magnetoresistance driven by intrinsic electronic structure. Here we explore electronic transport in magnetic members of the latter family of semimetals and find that XMR is strongly modulated by magnetic order. In particular, CeSb exhibits XMR in excess of $1.6 times 10^{6}$ % at fields of 9 T while the magnetoresistance itself is non-monotonic across the various magnetic phases and shows a transition from negative magnetoresistance to XMR with field above magnetic ordering temperature $T_{N}$. The magnitude of the XMR is larger than in other rare earth monopnictides including the non-magnetic members and follows an non-saturating power law to fields above 30 T. We show that the overall response can be understood as the modulation of conductivity by the Ce orbital state and for intermediate temperatures can be characterized by an effective medium model. Comparison to the orbitally quenched compound GdBi supports the correlation of XMR with the onset of magnetic ordering and compensation and highlights the unique combination of orbital inversion and type-I magnetic ordering in CeSb in determining its large response. These findings suggest a paradigm for magneto-orbital control of XMR and are relevant to the understanding of rare earth-based correlated topological materials.
We present reflectance measurements in the infrared region on a single crystal the rare earth scandate DyScO3. Measurements performed between room temperature and 10 K allow to determine the frequency of the infrared-active phonons, never investigated experimentally, and to get information on their temperature dependence. A comparison with the phonon peak frequency resulting from ab-initio computations is also provided. We finally report detailed data on the frequency dependence of the complex refractive index of DyScO3 in the terahertz region, which is important in the analysis of terahertz measurements on thin films deposited on DyScO3.
Using Fourier-transform infrared spectroscopy and optical ellipsometry, room temperature spectra of complex conductivity of single crystals of hexaborides Gd$_x$La$_{1-x}$B$_6$, $x$(Gd)$=0$, 0.01, 0.1, 0.78, 1 are determined in the frequency range 30$-$35000$~cm^{-1}$. In all compounds, in addition to the Drude free-carrier spectral component, a broad excitation is discovered with the unusually large dielectric contribution $Delta$$varepsilon$=5000 -- 15000 and non-Lorentzian lineshape. It is suggested that the origin of the excitation is connected with the dynamic cooperative Jahn-Teller effect of B$_6$ clusters. Analysis of the spectra together with the results of DC and Hall resistivity measurements shows that only 30$-$50$%$ of the conduction band electrons are contributing to the free carrier conductivity with the rest being involved in the formation of an overdamped excitation, thus providing possible explanation of remarkably low work function of thermoemission of Gd$_x$La$_{1-x}$B$_6$ and non-Fermi-liquid behavior in GdB$_6$ crystals.
The magnetic susceptibility of the 1/1 approximants to icosahedral quasicrystals in a series of Cd85-xMgxTb15 (x = 5, 10, 15, 20) alloys was investigated in detail. The occurrence of antiferromagnetic to spin-glass-like transition was noticed by increasing Mg. Transmission electron microscopy analysis evidenced a correlation between the magnetic transition and suppression of the monoclinic superlattice ordering with respect to the orientation of the Cd4 tetrahedron at T > 100 K. The possible origins of this phenomenon were discussed in detail. The occurrence of the antiferromagnetic to spin-glass -like magnetic transition is associated with the combination of chemical disorder due to a randomized substitution of Cd with Mg and the orientational disorder of the Cd4 tetrahedra.
Crystals of solid solutions Bi(1-x)R(x)FeO(3),here R= La, Dy, Gd, were obtained with x <=0.7. Solid solutions of the stated rare earths, as x is increased from 0 to 0.7, have one and the same sequence of five crystal structures (rhombohedral C3v 6, triclinic C1 1,orthorhombic D2 6,orthorhombic D2 5, orthorhombic C2v 9). The ferroelectric-paraelectric transition occurs in rhombohedral and triclinic crystals at T=810-560{deg}C.The high temperature modifications are orthorhombic and cubic. The orthorhombic structure C2v 9 holds up to 1180{deg}C.The ferroelectric domain structure was distinguished in all types of crystals. No magnetoelectric effect (MEE) was detected in the orthorhombic crystals with the D2 (222) symmetry class. But the mm2 crystals were found to have both quadratic and linear MEE.The value of the quadratic effect is considerably smaller than that ofthe linear one. Magnetoelectric hysteresis takes place in the crystals. The tensorial properties of the obtained crystals are analyzed from the viewpoint of crystal symmetry.
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