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Structural, magnetic and electronic properties of partially inverted Cobalt Ferrite with composition Co 1.5 Fe 1.5 O 4 is discussed in the present work. Single phase (SG: Fd3m) sample is synthesized by co-precipitation technique and subsequent air annealing. The values of saturation magnetization obtained from careful analysis of approach to saturation in initial M(H) curves are used to determine spin states of Co ions in tetrahedral (T H ) and octahedral (O H ) sites. Spin states of Co 3+ ions in T H sites, which has not been reported in literature, were found to be in high spin state. Temperature variation of magnetic parameters has been studied. The sample shows magneto-crystalline anisotropy with two clearly distinct pinning centers. Oxygen K-edge and Fe as well as Co L 2,3 -edge X-ray absorption (XAS) spectra have been used as complementary measurements to study crystal field splitting and core hole effects on transition metal (TM) 3d orbitals. The ratio of intensities of t 2g and e g absorption bands in O-K edge XAS spectrum is used to estimate the spin states of Co ions at O H and T H sites. The results are in agreement with those obtained from magnetization data, and favors Co 3+ ions in T H sites in high spin states. Normalized areas of the satellite peaks in TM L 2 , 3 -edge XAS spectra have been used to estimate 3d n+1 L contribution in ground state wave function and the contributions were found to be significant. [ABSTRACT FROM AUTHOR]

We report the improvement of electric and magnetic properties of the chemical routed samples of Co 1.25 Fe 1.75 O 4 ferrite. Synchrotron X-ray diffraction pattern confirmed the cubic spinel structure in all samples. Raman spectroscopy provided the information of mixed-type cubic spinel structure, where Co 2+ and Fe 3+ ions order both in octahedral and tetrahedral sites. The thermal heat treatment has brought a systematic change in electric polarization and magnetic parameters. At a critical annealing temperature ( T AN ) of 800 °C, the sample has shown the highest magnetic coercivity ~596 Oe and relatively large squareness ~0.5. The electrical conductivity, dielectric loss and dielectric constant have decreased with increase of T AN . The dielectric constant becomes stable for T AN above 800 °C. The samples annealed in the temperature range 900–1000 °C have shown a good signature of ferroelectric polarization, although it is under saturation value and leakage of polarization due to conductive effect is observed. This work shows the scope of the improvement of electric polarization due to capacitive effect on increasing the annealing temperature of as-prepared Co ferrite sample. [ABSTRACT FROM AUTHOR]

We have prepared a composite of ferrimagnetic ferrite Co 1.75 Fe 1.25 O 4 and non-magnetic oxide BaTiO 3 . The ferrite composition Co 1.75 Fe 1.25 O 4 has been prepared by chemical co-precipitation and subsequently heated at different temperatures. The heat treated ferrite powder has been mixed with BaTiO 3 powder with mass ratio 1:1 and the mixed powder has been finally heated at 1000 °C to form composite material. Structural phase of the composite material has been confirmed by high quality Synchrotron X-ray diffraction pattern and Micro-Raman spectra. The grain surface morphology and elemental composition have been studied by Scanning electron microscope and Energy dispersive X-ray analysis. The distribution of magnetic exchange interactions and blocking behavior of the ferrimagnetic grains in composite samples has been understood by analyzing the temperature and magnetic field dependence of dc magnetization. Finally, information on modified micro-structure and ferrimagnetic parameters in composite samples has been obtained as the variation of annealing temperature of the ferrite component before making composite. [ABSTRACT FROM AUTHOR]

• Cr doped hematite synthesised by chemical route and heat treatment. • Crystal structure confirmed by Synchrotron X-ray diffraction and Raman spectroscopy. • Morin transition is absent and field induced spin flipping is observed. • The samples showed superparamagnetism and canted antiferro-magnetic spin order. • Core-shell model was used to understand the evolution of spin order with heat treatment. The Cr doped hematite (α-Fe 1.4 Cr 0.6 O 3) system has been prepared by chemical route. The chemical routed sample has been thermally annealed at different temperatures in the range 800–1000 °C to study modified lattice structure and magnetic spin order. The present Cr doped hematite samples do not exhibit Morin transition, a typical temperature that marks spin orientation from in-plane spin to out of plane directions in hematite system. A distinct change in magnetic properties has been seen by increasing the annealing temperature. The sample prepared by annealing at 800 °C showed superparamagnetic blocking of particles below 38 K. Ac susceptibility data have been used to study the mechanism of spin dynamics around the blocking temperature. Such blocking behaviour of particles is not observed in the samples annealed at 900–1000 °C. The modified spin order in the samples has been understood by using core-shell model of antiferromagnetic particles. Mössbauer spectra of the samples have confirmed a transformation of the spin order with the increase of annealing temperature and support the features observed from dc magnetic measurements. [ABSTRACT FROM AUTHOR]

• Cr doped hematite synthesised by mechanical alloying. • Crystal structure study by Synchrotron X-ray diffraction and Raman spectroscopy. • Magnetic properties using dc magnetization and Mossbauer spectroscopy. • Correlation between structure and properties. • A detailed report of structure, magnetic modification and conductivity in Cr doped hematite. The solid solution of Fe 2-x Cr x O 3 (x = 0.2–0.8) has been prepared by mechanical alloying of α-Fe 2 O 3 and α-Cr 2 O 3 oxides and subsequent heat treatment. The lattice structure and properties of the heat treated samples differed from the as-alloyed samples. High quality synchrotron X-ray diffraction patterns have shown an inhomogeneous structure of α-Fe 2 O 3 and α-Cr 2 O 3 phases in as-alloyed samples. The heat treatment has homogenized structure and successfully incorporated the Cr atoms into lattice sites of the Fe atoms in α-Fe 2 O 3. The soft ferromagnetic properties with signature of two Morin transitions have been observed in the as-alloyed samples. A canted antiferromagnetic spin order has appeared in the heat treated samples, irrespective of Cr content in Fe 2-x Cr x O 3. The spin flop transition has been observed at a critical magnetic field that depends on Cr content in the system. The Mössbauer spectra at room temperature have suggested a non-uniform distribution of magnetic spin order of Fe and Cr ions in rhombohedral structure. The electrical conductivity of the heat treated samples has shown enhancement with the increase of Cr content in α-Fe 2 O 3 structure. [ABSTRACT FROM AUTHOR]

• Crossover of magnetic ground state: ferromagnetic to antiferromagnetic. • Metal-insulator transition is observed. • Field induced metamagnetic transition: suggests coexistence of magnetic phases. • Anomaly in the unit cell parameter across magnetic transition temperatures describe spin lattice coupling. We have observed cross over from Ferromagnetism (FM) to Anti-ferromagnetism (AFM) accompanied by spin lattice coupling in La 0.7- x Bi x Sr 0.3 MnO 3 as La is partially replaced by Bi (0.25 ≤ x ≤ 0.40) through structural, magnetization and electrical resistivity studies. Ferromagnetic metallic (FMM) phase observed in x = 0.25 sample transforms to antiferromagnetic insulating (AFI) phase with increasing Bi content (x = 0.40). The step like behavior in M(H), i.e. the metamagnetic transition, describes the field induced antiferromagnetic to ferromagnetic transition in x = 0.30 and 0.35 samples. The irreversibility in the field dependent resistivity and magnetization suggests the competitive phase coexistence, between AFM and FM phases, in x = 0.30 and 0.35 samples. The anomaly in the structural parameters across the electrical and magnetic transition observed from the analysis of synchrotron X-ray diffraction data, at low temperatures, establishes a strong interplay between spin lattice coupling in all four samples studied here. The present study thus clearly brings out cross over from FMM to AFI state as Bi concentration increases in La 0.7- x Bi x Sr 0.3 MnO 3. [ABSTRACT FROM AUTHOR]

• Hex-Sr 0.6 Ba 0.4 MnO 3 shows short-range (SR) to long-range (LR) magnetic ordering. • Local structural changes in MnO 6 octahedra leads to SR to LR magnetic correlation. • Below the SR-LR crossover temperature, dipole-cluster glass state is observed. • Competitive-frustration among spin-exchange is responsible for dipole glass origin. • Negative magneto-dielectric coupling upto ~1.2% is observed. The crystal structure of hexagonal-Sr 0.6 Ba 0.4 MnO 3 allows various competing superexchange interactions, leading to intriguing magnetic properties. Local structural changes with temperature modify the overlapping between Mn and oxygen ions. Calculations based on our model spin-Hamiltonian reveal that the dominant antiferromagnetic superexchange interaction between the linearly oxygen-linked Mn4+ ions results in short range correlations (SRC), manifesting a smooth drop in magnetization below 325 K. Dominance of superexchange interaction changes its allegiance towards the non-linearly oxygen-linked Mn-O-Mn interactions, onsetting long-range correlations (LRC) below 225 K. Below the SRC-LRC crossover temperature, electrical response arising from the interacting dipoles exhibits power-law divergent behaviour of their relaxation time, upon cooling. Non-ergodic character of the dipole-cluster glass state is examined via the indispensable aging and rejuvenation effects, similar to the spin glasses. Competitive-frustration among spin-exchange and local-strain is reckoned as responsible for the electrical glass origin. [ABSTRACT FROM AUTHOR]