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Two multiferroic perovskite systems - HoCr0.9Fe0.1O3 (HCFO) and HoCr0.9Mn0.1O3 (HCMO) have been prepared by the solid state ceramic method. Rietveld refinement of powder x-ray diffraction patterns of systems give the values of structural parameters and reveal that both the samples crystallize in orthorhombic symmetry. Magnetization measurements show the two samples exhibit two magnetic transitions—paramagnetic to canted antiferromagnetic (CAFM of Cr3+ sub-lattice) transition like HoCrO3 at ~140 K and corresponding to reorientation of Ho3+ spins at ~7 K. Sample HCMO shows an additional discontinuity (in M—T curve) at 35 K. Results are suggestive of the canting angle (in CAFM) to be larger in Mn substituted sample than in Fe substituted one, a reduced strength of AFM interaction in HCMO sample. Dielectric measurements have been made as a function of frequency and temperature. The samples show ferroelectric to paraelectric transitions at Tc ~ 515 K for HCFO and ~460 K for HCMO at an excitation frequency of 1 kHz.

The evolution of reversible room temperature ferromagnetism (RTFM) has been investigated in Co- and Fe-doped (5% each) and non-doped CeO2 polycrystalline samples. Specimens with different oxygen vacancy (VO) concentration including the (i) as-synthesized, (ii) hydrogenated and (iii) re-annealed in air were investigated using SQUID magnetometry, x-ray diffraction and x-ray photoelectron spectroscopy. The influence of the electronic properties on the RTFM was examined/analysed systematically. Our findings confirm that the ferromagnetism observed in CeO2 originates due to the oxygen vacancies, supporting the VO mediated ferromagnetic exchange mechanism. Additionally, the cationic (cerium and transition metal) valence states play a crucial role.

We report the results of electronic and magnetic properties of poly-crystalline Zn1-xMxO (M = Co and Mn) pellets studied by XRD, VSM and XPS. The specimens were synthesized by solid state reaction method using high purity oxides. Samples exhibit Wurtzite hexagonal symmetry and show interesting magnetic properties. The Co (5%) doped sample prepared by heating in air shows a paramagnetic state in agreement with several claims. But the sample prepared by heating in Ar atmosphere depicts ferromagnetic ordering. Addition of 2% Mn in it further enhances its magnetic moment. The specimens ZnCoO (Ar heated) and ZnCoMnO were hydrogenated at 550°C that caused a significant change in their magnetization. The Co doped ZnO shows a robust increment in the magnetic moment but the Mn doping does not seem to respond to hydrogenation. O 1s XPS results show clear evidence of oxygen depletion for the samples prepared by heating in Ar atmosphere and a further depletion upon hydrogenation. Results suggest oxygen vacancies as the basic origin for room temperature ferromagnetism in doped ZnO.

The wide band gap semiconductor ZnO when doped with a very low percent of some transition metal ions can exhibit above room temperature ferromagnetism, transforming it into a unique compound for spin-electronic applications. In the present work we have compared the electronic structure of two polycrystalline Zn1-xMnxO pellets (for x=0.02 and 0.04), prepared by low temperature processing, and carefully characterized. The Rietveld refinement of the XRD patters established that the samples have the ZnO lattice with ZnS type Wurtzite hexagonal symmetry and no detectable impurities. The samples exhibit distinctly different magnetic properties. The pure ZnO pellet shows a diamagnetic behaviour, the 2% sample displayed a clear FM ordering at 300 K while the 4% sample did not show any ordering even upon cooling. Their electronic structure has been investigated using x-ray absorption and x-ray photoemission spectroscopy with an aim to find out how the changes in the electronic structure can correlate to the magnetic properties in such diluted magnetic semiconductor materials. The results show that most of the Mn ions of the ferromagnetic sample are in the divalent state. For the higher Mn percent nonmagnetic sample, a larger contribution of higher oxidation Mn states are dominant and the oxygen content also increases. The two factors can be correlated to the suppressed ferromagnetism, though it is hard to exactly predict that which of these two factors weighs more.

Inverse magnetic susceptibility χ−1 has been measured as a function of temperature for five alloys in the series (Fe1−xCox)2P. Short range magnetic order above the Curie temperature in the studied alloys was observed. Paramagnetic moments have been obtained using χ−1–T curves. These are much larger than saturation moments showing dominance of the itinerant nature of magnetism. The degree of itinerancy is smaller in the orthorhombic phase than in the hexagonal phase. Substitution of Co causes magnetization to monotonically decrease. Anisotropy drops in the hexagonal phase with increasing Co but in the orthorhombic phase it again progressively increases.

Structural and magnetic properties of (Fe0.93Ni0.07)2P have been investigated by means of powder x-ray and neutron diffraction, magnetization and paramagnetic susceptibility measurements over a temperature range of 10–500 K. The system crystallizes in the Fe2P type hexagonal structure ( space group, Z = 3) in which the Ni atoms occupy the tetrahedral MI sites with total preference. Refined values of the cell parameters and bond distances are found slightly higher than those for Fe2P and the atomic positional parameters are found quite close to those reported for the parent compound Fe2P. The temperature dependence of the magnetization shows a sharp magnetic phase transition around 298(5) K. However there is difference of the zero-field cooled and field cooled modes of the magnetization, which is indicative of the formation of ferromagnetic clusters. The ferromagnetic to paramagnetic transition shifts towards the higher temperature side with increase in the applied magnetic field, which indicates that the phase transition is a field induced type first-order magnetic phase transition. There is no crystallographic structural transition associated with the magnetic phase transition. The transition is caused by the change in the c/a ratio. The alloy retains the ferromagnetic order of Fe2P with the moments orienting along the [001] direction. The Rhodes–Wohlfarth ratio (µp/µs) of (Fe0.93Ni0.07)2P is found to be 1.53 (>1), showing itinerant magnetism in this compound. At 297 K the magnetic moment at the MI site is found negligible but at the MII site it is ~0.51 µB. The observed non-linearity above Tc in the χ−1–T curve gives clear evidence of the presence of short range magnetic order above Tc. The moments at the MII sites in the paramagnetic state and the exchange interactions are responsible for the short range one-dimensional ferromagnetic chains along [001] well above the Tc in (Fe0.93Ni0.07)2P.