Ferromagnetism from non-magnetic ions: Ag-doped ZnO.

To develop suitable ferromagnetic oxides with Curie temperature (TC) at or above room temperature for spintronic applications, a great deal of research in doping ZnO with magnetic ions is being carried out over last decade. As the experimental results on magnetic ions doped ZnO are highly confused and controversial, we have investigated ferromagnetism in non-magnetic ion, Ag, doped ZnO. When Ag replaces Zn in ZnO, it adopts 4d9 configuration for Ag2+ which has single unpaired spin and suitable exchange interaction among these spins gives rise to ferromagnetism in ZnO with above room temperature TC. Experimentally, we have observed room temperature ferromagnetism (RTFM) in Ag-doped ZnO with Ag concentration varied from 0.03% to 10.0%. It is shown that zinc vacancy (VZn) enhances the ferromagnetic ordering (FMO) while oxygen vacancy (VO) retards the ferromagnetism in Ag-doped ZnO. Furthermore, the theoretical investigation revealed that VZn along with Ag2+ ions play a pivotal role for RTFM in Ag-doped ZnO. The Ag2+-Ag2+ interaction is ferromagnetic in the same Zn plane whereas anti-ferromagnetic in different Zn planes. The presence of VZn changes the anti-ferromagnetic to ferromagnetic state with a magnetic coupling energy of 37 meV. Finally, it has been established that the overlapping of bound magnetic polarons is responsible for RTFM in low doping concentration. However, anti-ferromagnetic coupling sets in at higher doping concentrations and hence weakens the FMO to a large extent.

Origin of ferromagnetism in Cu-doped ZnO.

It is widely reported during last decade on the observation of room temperature ferromagnetism (RTFM) in doped ZnO and other transition metal oxides. However, the origin of RTFM is not understood and highly debated. While investigating the origin of RTFM, magnetic ion doped oxides should be excluded because it is not yet settled whether RTFM is intrinsic or due to the magnetic ion cluster in ZnO. Hence, it is desirable to investigate the origin of RTFM in non-magnetic ion doped ZnO and Cu-doped ZnO will be most suitable for this purpose. The important features of ferromagnetism observed in doped ZnO are (i) observation of RTFM at a doping concentration much below than the percolation threshold of wurtzite ZnO, (ii) temperature independence of magnetization and (iii) almost anhysteretic magnetization curve. We show that all these features of ferromagnetism in ZnO are due to overlapping of bound magnetic polarons (BMPs) which are created by exchange interaction between the spin of Cu2+ ion and spin of the localized hole due to zinc vacancy [Formula: see text]. Both the experimental and theoretical investigation show that the exchange interaction between Cu2+-Cu2+ ions mediated by [Formula: see text] is responsible for RTFM in Cu-doped ZnO.

Congenital Giant Teratoma Arising from the Hard Palate: A Rare Clinical Presentation.

Teratomas are rare tumours which originate from all 3 germs cell layers namely endoderm, mesoderm and ectoderm, with varying proportions of each component. The most common site of teratoma is in the sacro-coccygeal region. Teratomas are generally benign and have well appreciable clinical and histopathological features. Incidence of congenital teratoma is 1 in 4000. In head and neck region congenital teratomas usually associated with other anomalies like cystic hygroma and cleft palate with an incidence of 1 in 400. The approximately reported incidence of palatal teratoma is 1 in 35000 to 40000 live-births. Upper airway difficulty causes anticipated functional problems at hypopharynx. The prognosis of palatal teratoma mostly depends on the risk and extent of neonatal respiratory distress. We present a rare case of congenital teratoma arising from the hard palate in a new born girl. The outcome in this case was bad due to the large mass causing respiratory difficulty and bleeding from the ruptured cystic areas leading to hypovolemic shock. After two hours of delivery, baby expired.