The electronic structure of double perovskite PrMnNiO was studied using core x-ray photoelectron spectroscopy and x-ray absorption spectroscopy. The 2p x-ray absorption spectra show that Mn and Ni are in 4+  and 2+  states respectively. Based on charge transfer multiplet analysis of the 2p XPS spectra of both ions, we find charge transfer energies [Formula: see text] of 3.5 and 2.5 eV for Ni and Mn respectively. The ground state of Ni and Mn ions reveal a higher d electron count of 8.21 and 3.38 respectively as compared to the ionic values. The partial density of states clearly show a charge transfer character of the system for U  -  J [Formula: see text] 2 eV. The O 1s edge absorption spectra reveal a band gap of 0.9 eV, which is close to the value estimated from analysis of Ni and Mn 2p photoemission and absorption spectra. The combined analysis of nature of spectroscopic data and first principles calculations reveal that the material is a p  -  d type charge transfer insulator with an intermediate covalent character according to the Zannen-Sawatzy-Allen phase diagram.

The structural, magnetic, and electronic properties of NdFe0.5Mn0.5O3 have been studied in detail using bulk magnetization, neutron/x-ray diffraction and first principles density functional theory calculations. The material crystallizes in the orthorhombic P bnm structure, where both Mn and Fe occupy the same crystallographic site (4b). Mn/Fe sublattice of the compound orders in to a G-type antiferromagnetic phase close to 250 K where the magnetic structure belongs to Γ1 irreducible representation with spins aligned along the crystallographic b direction. This is unconventional in the sense that most of the orthoferrites and orthochromites order in the Γ4 representation below the Néel temperature.This magnetic structure then undergoes a complete spin reorientation transition with temperature in the range 75 K > ∼ T > ∼ 25 K where the magnetic structure exists as a sum of two irreducible representations (Γ1+Γ2) as seen from neutron diffraction measurements. At 6 K, the magnetic structure belongs entirely to Γ2 representation with spins aligned antiferromagnetically along the crystallographic c direction having a small ferromagnetic component (Fx). The unusual spin reorientation and correlation between magnetic ground state and electronic structure have been investigated using first principles calculations within GGA+U and GGA+U+SO formalisms.

No abstract

No abstract

A significant magnetocaloric effect (MCE) has been revealed in our investigation on polycrystalline Nd0.5Dy0.5FeO3 below 30 K. Observed magnetization of the system at low temperature is 32% higher than the expected average magnetization of NdFeO3 and DyFeO3. Such an enhancement in the magnetization led to a large change in magnetic entropy (10.4 Jkg−1 K−1) at 4 K. The observed entropy change is remarkable considering the higher natural abundance of Nd compared to that of Dy and negligible MCE seen in case of NdFeO3. Theoretical calculations performed using mean-field approximation and Monte Carlo simulations on an Ising type spin model indicate that the high magnetocaloric effect is caused primarily by the ordering of rare-earth ions in C-type antiferromagnetic state in presence of molecular exchange field created by Fe ions.