Ferromagnetic interactions in Mn3+ based perovskites.

La0.7Sr0.3Mn(3+)0.85Sb(5+)0.15O3 and La0.7Sr0.3Mn(3+)0.8Sb(5+)0.1Ge(4+)0.1O3 compounds with dominantly isovalent Mn3+ ions were studied by neutron powder diffraction and magnetization measurements. The compounds are basically ferromagnetic, with magnetic moments slightly above of 3 µB/Mn. Upon temperature decrease, the compounds exhibit structural transition from a rhombohedral phase to orbitally disordered orthorhombic one. The structural transitions occur well above the temperature of magnetic ordering (Tc ≈ 130 K). It is suggested that the ferromagnetic state is governed by the positive part of superexchange interactions Mn(3+)‒O‒Mn(3+), which is enhanced by Mn(eg)‒O(2p) hybridization.

Magnetic and structural phase transitions in La0.5Sr0.5CoO(3-δ) (0 ≤ δ < 0.3) cobaltites.

The evolution of the crystal structure and the magnetic properties was investigated in the La0.5Sr0.5CoO(3-δ) (0 < δ < 0.3) system as a function of the oxygen deficit δ. Compounds with a low oxygen deficit (δ < 0.1) are shown to be predominantly ferromagnetic, while further increase (δ > 0.1) gradually changes the magnetic structure from ferromagnetic to G-type antiferromagnetic and causes a structural transition from rhombohedral to cubic symmetry. Resistivity and magnetoresistance at low temperature increase with increasing of oxygen vacancies. It is argued that oxygen reduction facilitates stabilization of the high spin state of Co(3+) ions. Antiferromagnetic interactions between cobalt ions in the high spin state are found to dominate in compounds with the oxygen deficit δ > 0.18.

Composition- and temperature-driven structural transitions in Bi(1-x)Ca(x)FeO3 multiferroics: a neutron diffraction study.

Neutron powder diffraction and magnetization measurements of the Bi(1-x)Ca(x)FeO3 (0.05 ≤ x ≤ 0.14) compounds were carried out to follow the effect of the heterovalent A-site doping on the long-range structure and magnetic properties of the BiFeO3 multiferroic. Ca substitution induces the appearance of weak ferromagnetism in the initial ferroelectric R3c phase, but modifies the picture of polar displacements, so the average PbZrO3-like antiferroelectric structure is stabilized at x = 0.11. Further increase of the Ca content leads to transformation of the antipolar ionic shifts to give rise to the Pbam → Imma transition near x = 0.14. A structural study performed for the x = 0.05 compound at high temperature revealed the R3c → Pnma phase transition at 950 K. For x = 0.1 samples, an intermediate heating-induced structure separating the R3c and Pnma phases was found.

Neutron diffraction study and magnetic properties of La(1-x)Ba(x)CoO(3) (x = 0.2 and 0.3).

The magnetic properties together with the crystal and magnetic structures of the cobaltites La(1-x)Ba(x)CoO(3) (for x = 0.2 and 0.3) are determined by DC magnetization, AC magnetic susceptibility and neutron powder diffraction measurements over a broad spectrum of temperatures. For x = 0.3 a rhombohedral structure with space group [Formula: see text] is maintained at all temperatures below 300 K. On the other hand, for x = 0.2 the refinement of the neutron data below 150 K indicates the coexistence of two structures, [Formula: see text] (rhombohedral) and Pbnm (orthorhombic), respectively, in a ratio of ∼48/52. Both compounds (x = 0.2 and 0.3) show a ferromagnetic long range order. The data fit well with the Co(3+) ions in the intermediate spin state and the Co(4+) ions in a low spin state.

Electronic structure of A- and B-site doped lanthanum manganites: a combined X-ray spectroscopic study.

The electronic properties of a series of colossal magnetoresistance (CMR) compounds, namely LaMnO3, La(1-x)Ba(x)(MnO3 (0.2 < or = x < or = 0.55), La(0.76)Ba(0.24)Mn(0.84)Co(0.16)O3, and La(0.76)Ba(0.24)Mn(0.78)Ni(0.22)O3, have been investigated in a detailed spectroscopic study. A combination of X-ray photoelectron spectroscopy (XPS), X-ray emission spectroscopy (XES), X-ray absorption spectroscopy (XAS), and resonant inelastic X-ray scattering (RIXS) was used to reveal a detailed picture of the electronic structure in the presence of Ba, Co, and Ni doping in different concentrations. The results are compared with available theory. The valence band of La(1-x)()Ba(x)MnO3 (0 < or = x < or = 0.55) is dominated by La 5p, Mn 3d, and O 2p states, and strong hybridization between Mn 3d and O 2p states is present over the whole range of Ba concentrations. Co-doping at the Mn site leads to an increased occupancy of the e(g) states near the Fermi energy and an increase in the XPS valence band intensity between 0.5 and 5 eV, whereas the Ni-doped sample shows a lower density of occupied states near the Fermi energy. The Ni d states are located in a band spanning the energy range of 1.5-5 eV. XAS spectra indicate that the hole doping leads to mixed Mn 3d-O 2p states. Furthermore, RIXS at the Mn L edge has been used to probe d-d transitions and charge-transfer excitations in La(1-x)Ba(x)MnO3.