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Register a new userEnhancement of ferroelectricity in Cr-doped Ho_2Ti_2O_7
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A series of polycrystalline pyrochlore rare-earth titanate Ho_{2-x}Cr_xTi_2O_7 are synthesized in order to enhance the ferroelectricity of pyrochlore Ho2Ti2O7. For the sample close to the doping level x=0.4, a giant enhancement of polarization P up to 660muC/m2 from 0.54muC/m2 at x=0 is obtained, accompanied with an increment of ferroelectric transition point Tc up to ~140K from ~60K. A magnetic anomaly at T~140K together with the polarization response to magnetic field, is identified, implying the multiferroic effect in Ho2-xCrxTi2O7.
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The effect of Cr doping with nominal compositions Mn2-xCrxO3 (0 less than equal to x less than equal to 0.10) has been undertaken to investigate its effect on structural, magnetic, dielectric and magnetoelectric properties. The Cr doping transformed the room temperature crystal structure from orthorhombic to cubic symmetry. Similar to alpha-Mn2O3, two magnetic transitions have been observed in the Cr doped samples. The effect of Cr doping is significant on the low temperature transition i.e. the lower magnetic transition shifted towards higher temperature (25 K for pristine to 40 K for x=0.10) whereas the high temperature transition decreases slightly with increasing Cr content. A clear frequency independent transition is observed in complex dielectric measurements for all compositions around high temperature magnetic ordering. Interestingly, the magnetodielectric behaviour enhanced enormously approx 21% with Cr substitution as compared to pristine Mn2O3.
We present a comparative, theoretical study of the doping dependence of the critical temperature $T_C$ of the ferromagnetic insulator-metal transition in Gd-doped and O-deficient EuO, respectively. The strong $T_C$ enhancement in Eu$_{1-x}$Gd$_x$O is due to Kondo-like spin fluctuations on the Gd sites, which are absent in EuO$_{1-x}$. Moreover, we find that the $T_C$ saturation in Eu$_{1-x}$Gd$_x$O for large $x$ is due to a reduced activation of dopant electrons into the conduction band, in agreement with experiments, rather than antiferromagnetic long-range contributions of the RKKY interaction. The results shed light on possibilities for further increasing $T_C$.
We present results of a combined density functional and many-body calculations for the electronic and magnetic properties of the defect-free digital ferromagnetic heterostructures obtained by doping GaAs with Cr and Mn. While local density approximation/(+U) predicts half-metallicity in these defect-free delta-doped heterostructures, we demonstrate that local many-body correlations captured by Dynamical Mean Field Theory induce within the minority spin channel non-quasiparticle states just above $E_F$. As a consequence of the existence of these many-body states the half-metallic gap is closed and the carriers spin polarization is significantly reduced. Below the Fermi level the minority spin highest valence states are found to localize more on the GaAs layers being independent of the type of electronic correlations considered. Thus, our results confirm the confinement of carriers in these delta-doped heterostructures, having a spin-polarization that follow a different temperature dependence than magnetization. We suggest that polarized hot-electron photoluminescence experiments might bring evidence for the existence of many-body states within the minority spin channel and their finite temperature behavior.
We report on Cr doping effect in Mn3Sn polycrystalline films with both uniform and modulation doping. It is found that Cr doping with low concentration does not cause notable changes to the structural and magnetic properties of Mn3Sn, but it significantly enhances the anomalous Hall conductivity, particularly for modulation-doped samples at low temperature. A Hall conductivity as high as 184.8 {Omega}-1 cm-1 is obtained for modulation-doped samples at 50 K, in a sharp contrast to vanishingly small values for undoped samples at the same temperature. We attribute the enhancement to the change of Fermi level induced by Cr doping
A class of materials known as ``ferroelectric metals was discussed theoretically by Anderson and Blount in 1965 [Phys. Rev. Lett. 14, 217 (1965)], but to date no examples of this class have been reported. Here we present measurements of the elastic moduli of Cd2Re2O7 through the 200 K cubic-to-tetragonal phase transition. A Landau analysis of the moduli reveals that the transition is consistent with Cd2Re2O7 being classified as a ``ferroelectric metal in the weaker sense described by Anderson and Blount (loss of a center of symmetry). First-principles calculations of the lattice instabilities indicate that the dominant lattice instability corresponds to a two-fold degenerate mode with Eu symmetry, and that motions of the O ions forming the O octahedra dominate the energetics of the transition.
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