Polycrystalline YMn 1-x Fe x O 3 (YMFO x ) (0 ≤ x ≤ 0.1) compounds have been prepared in single phase and characterized by synchrotron X-ray diffraction, X-ray absorption near edge spectroscopy, magnetization, and dielectric measurements. Iron-substitution in hexagonal

In contrast to UO 2 and PuO 2 , there is no consensus on the existence of mixed valence NpO 2+x , resulting in a gap between NpO 2 and Np 2 O 5 (the highest binary oxide of Np) in the Np-O phase diagram. We now show NpO 2+x via Np L III Extended X-ray Absorption Fine Structure (EXAFS) spectra of three samples of NpO 2 that, analogous to U and Pu, exhibit multisite Np-O distributions with varying numbers of oxygen atoms at 1.87-1.91 Å. This is supported by the diffraction pattern of the sample with the largest amount of this oxo-type species that can be refined with both the simple fluorite structure and a trigonal one related to -U 4 O 9. The implied Np(V)-bridging oxo moieties as well as possible indications of OH¯ found by detailed EXAFS analysis suggest that NpO 2+x more closely resembles PuO 2+x than UO 2+x. An additional common characteristic suggested by the EXAFS and X-Ray Diffraction (XRD) is the phase separation into NpO 2 and what would be previously unreported Np 4 O 9(-) , indicative of O clustering.

Magnetic structure evolution of multiferroic hexagonal YMn 1-x Fe x O 3 (x= 0, 0.05, and 0.1) has been studied by carrying out detailed temperature-dependent neutron diffraction at zero and 5T fields.Thermodynamic data confirm antiferromagnetic ordering at T N in all the compositions. Our sub-T N neutron diffraction results assign the magnetic structure of pure YMnO 3 to Γ 1 irreducible representation. Over the perturbative-doping range, magnetic structure changes via Γ 1 +Γ 2 for YMn 0.95 Fe 0.05 O 3 on to Γ 2 for YMn 0.9 Fe 0.1 O 3 , as the maiden compositional analogue of spinreorientation; its occurrence in temperature-domain already reported for several manganites.Moreover, while the large thermal isostructural changes observed above T N are subdued in the ordered state, small alterations by the applied 5T-field are relatively uniform across, confirming strong magneto-elastic nature of the system. Decrease of the ordered magnetic moment (µ ord ) and planar magnetic frustration noted with Fe-doping is enhanced by the applied field; apparently through canting.Keywords: Multiferroics, Magneto-elasticity, Frustrated Antiferromagnet, Neutron Diffraction. PACS: 75.50.Ee, 75.85.+t , 61.05.fm, 75.75 2Materials that possess coexistent magnetic and electrical orderings in single phase are known as Multiferroics. 1 Hexagonal YMnO 3 is a member of their special class known as geometrically frustrated multiferroics, and is one of the most intensively studied h-RMnO 3 . 2 It undergoes ferroelectric (FE) transition at T C ~ 900K and antiferromagnetic (AFM) ordering at T N ~70K. [3][4] The crystal structure of h-YMnO 3 consists of alternating layers of MnO 5 trigonal bipyramids. These bipyramids (in trimer-combinations, sharing a common planar Oxygen) are corner-linked in the abplane to form a triangular lattice, and are separated from one another along the c-axis by the planes of Y-ions. 5 The geometric effect of buckling of the trimerized MnO5-bipyramids is accompanied by the inversion-symmetry-breaking displacements of Y-layers, originating the ferroelectric polarization. 6 Regarding the magnetic structure, below T N the Mn 3+ moments order in the a-b plane, and form a 2D non-collinear spin structure, characterized by an angle of 120 o between the neighbouring spins. [7][8][9] Consequent to the 2D magnetism and triangular lattice, the magnetic structure of YMnO 3 is frustrated, characterized by the frustration factor f = |Θ CW |/T N , found to be as large as 7.8 for YMnO 3 . 10 Here, Θ CW is the (negative) intercept on the temperature-axis of the (interpolated) high-temperature T-linear (Curie-Weiss) inverse susceptibility of the independent-spins. The antiferromagnetic (AFM) order is governed by the in-plane Mn-O-Mn super-exchange interaction, whereas the Mn-O-O-Mn supersuper-exchange interaction between the stacked triangular planes is about two order of magnitude weaker. This weak inter-layer (z=0 and z=1/2), 4,7,11 configuration is the one that differentiates among the several magnetic structures proposed f...

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