Heavy fermion and Kondo lattice behavior in the itinerant ferromagnet CeCrGe3

Physical properties of polycrystalline CeCrGe$_{3}$ and LaCrGe$_{3}$ have been investigated by x-ray absorption spectroscopy, magnetic susceptibility $\chi(T)$, isothermal magnetization M(H), electrical resistivity $\rho(T)$, specific heat C($T$) and thermoelectric power S($T$) measurements. These compounds are found to crystallize in the hexagonal perovskite structure (space group \textit{P6$_{3}$/mmc}), as previously reported. The $\rho(T)$, $\chi(T)$ and C($T$) data confirm the bulk ferromagnetic ordering of itinerant Cr moments in LaCrGe$_{3}$ and CeCrGe$_{3}$ with $T_{C}$ = 90 K and 70 K respectively. In addition a weak anomaly is also observed near 3 K in the C($T$) data of CeCrGe$_{3}$. The T dependences of $\rho$ and finite values of Sommerfeld coefficient $\gamma$ obtained from the specific heat measurements confirm that both the compounds are of metallic character. Further, the $T$ dependence of $\rho$ of CeCrGe$_{3}$ reflects a Kondo lattice behavior. An enhanced $\gamma$ of 130 mJ/mol\,K$^{2}$ together with the Kondo lattice behavior inferred from the $\rho(T)$ establish CeCrGe$_{3}$ as a moderate heavy fermion compound with a quasi-particle mass renormalization factor of $\sim$ 45.Comment: 7 pages, 7 figures. Accepted by Journal of Physics: Condensed Matte

Tetramer Orbital-Ordering induced Lattice-Chirality in Ferrimagnetic, Polar MnTi2O4

Using density-functional theory calculations and experimental investigations on structural, magnetic and dielectric properties, we have elucidated a unique tetragonal ground state for MnTi2O4, a Ti^{3+} (3d^1)-ion containing spinel-oxide. With lowering of temperature around 164 K, cubic MnTi2O4 undergoes a structural transition into a polar P4_1 tetragonal structure and at further lower temperatures, around 45 K, the system undergoes a paramagnetic to ferrimagnetic transition. Magnetic superexchange interactions involving Mn and Ti spins and minimization of strain energy associated with co-operative Jahn-Teller distortions plays a critical role in stabilization of the unique tetramer-orbital ordered ground state which further gives rise to lattice chirality through subtle Ti-Ti bond-length modulations

μ\muSR and Neutron Diffraction Investigations on Reentrant Ferromagnetic Superconductor Eu(Fe{0.86}Ir{0.14})2As2

Results of muon spin relaxation ($\mu$SR) and neutron powder diffraction measurements on a reentrant superconductor Eu(Fe$_{0.86}$Ir$_{0.14}$)$_2$As$_2$ are presented. Eu(Fe$_{0.86}$Ir$_{0.14}$)$_2$As$_2$ exhibits superconductivity at $T_{\rm c\,on} \approx 22.5$~K competing with long range ordered Eu$^{+2}$ moments below $\approx 18$ K. A reentrant behavior (manifested by nonzero resistivity in the temperature range 10--17.5 K) results from an exquisite competition between the superconductivity and magnetic order. The zero field $\mu$SR data confirm the long range magnetic ordering below $T_{\rm Eu} = 18.7(2)$ K. The transition temperature is found to increase with increasing magnetic field in longitudinal field $\mu$SR which along with the neutron diffraction results, suggests the transition to be ferromagnetic. The neutron diffraction data reveal a clear presence of magnetic Bragg peaks below $T_{\rm Eu}$ which could be indexed with propagation vector k = (0, 0, 0), confirming a long range magnetic ordering in agreement with $\mu$SR data. Our analysis of the magnetic structure reveals an ordered magnetic moment of $6.29(5)\,\mu_{\rm B}$ (at 1.8 K) on the Eu atoms and they form a ferromagnetic structure with moments aligned along the $c$-axis. No change in the magnetic structure is observed in the reentrant or superconducting phases and the magnetic structure remains same for 1.8 K $\leq T \leq T_{\rm Eu}$. No clear evidence of structural transition or Fe moment ordering was found.Comment: 9 pages, 7 figures, to appear in Phys. Rev.

Magnetic structures of the Eu and Cr moments in EuCr2_{2} As2_{2} : Neutron diffraction study

The magnetic structures of the Eu2+ and Cr2+ moments in the nonsuperconducting parent compound EuCr2As2 have been determined by using neutron diffraction. While the Eu2+ moments order ferromagnetically with moments along the c direction at TC=21.0(1) K, the ordering temperature of the Cr2+ moments is found to be at very high temperature of 680(40) K by using magnetization measurements. The Cr2+ moments order in a G-type antiferromagnetic structure with moments along the c direction. According to this magnetic structure, the nearest-neighbor Cr2+ moments are antiferromagnetically aligned in the a−b plane as well as in the c direction. The ordered magnetic moment of the Eu2+ and Cr2+ amounts to 6.2(5)μB and 1.7(4)μB, respectively, at T=2 K

MeV N+-ion irradiation effects on -MoO3 thin films

In this work, modifications in the structural, vibrational, optical, and surface morphological properties of 2 MeV N+-ion irradiated -MoO3 thin films are studied. Nitrogen irradiation up to the fluence of 11015 ions cm−2 does not lead to any structural phase change. The irradiation induced formation of nanoscale defect structures at the film surface becomes more prominent at higher irradiation fluences, leading to the enhancement in the optical absorption behavior of the irradiated films. The possible role of energy loss process in the mechanism of modifying the surface morphology has been discussed

High temperature grown transition metal oxide thin films: tuning physical properties by MeV N+-ion bombardment

In this paper, we present a systematic study on tuning the physical properties of high temperature (373 K) grown transition metal oxide thin films by the effect of 2MeV nitrogen ion irradiation. Although we observe irradiation induced growth in crystallite sizes for both WO3 and MoO3 films, no structural phase change takes place in the films due to N+-ion beam irradiation even up to the fluence of 1 × 1015 N+ cm−2. On the other hand, irradiation leads to a significant increase in the optical absorption and the surface roughness of the films. These observations are corroborated by micro-Raman analysis. The results are attributed to the MeV ion–matter interaction