Upconversion nanoparticles on graphene based broadband photodetector showing unprecedented values of device parameters is demonstrated with response even for hand held domestic appliances.

The cluster-glass compound LaMn 0.7 Fe 0.3 O 3 was synthesized with average particle sizes ∼20, ∼90, and ∼300 nm. We observed a shift of the magnetic hysteresis loop in the field axis while the sample was cooled in an external magnetic field. The systematic shift of the hysteresis loops and the cooling field dependence of the shift indicated the phenomenon of exchange bias. The exchange bias field was found to be strongly dependent on the particle size, where the exchange bias field decreased considerably with an increase of particle size, and the weak effect of exchange bias was observed for particles with size ∼300 nm. A cluster-glass state with short range ferromagnetic clusters embedded in the spin-glass like host has been proposed, where the average size of the ferromagnetic cluster increases with particle size.

We investigate the magnetic properties of the nanoparticles of Co50Ni50 alloy embedded in the amorphous SiO2 host with volume fractions, ϕ=5% and 10%. The static and dynamic aspects of the magnetic properties are investigated by temperature and time dependence of low-field dc magnetization and frequency dependence of ac susceptibilities. The experimental results and analyses suggest that the dilution of the Co50Ni50 nanoparticles belongs to the crossover regime from superparamagnetic to superspin glass states, which are distinguished from the atomic canonical spin glasses.

An interesting scenario of unusual glassy states is observed from the dc and ac susceptibility measurements in LaMn0.5Fe0.5O3. The dc measurements at 5mT exhibit two distinct peaks at ∼20(Tg) and ∼255K(Tp). The large field-cooled effect and frequency-dependent results indicate a glassy state between Tg and Tp, while the relaxation dynamics does not show cooperative relaxation without aging, suggesting the existence of noninteracting clusters of frozen spin. On the other hand, the glassy state with clear evidence of a cooperative relaxation process is noticed below Tg, which has been characterized from the field- and frequency-dependent results associated with the evidence of aging. The nature of the cooperative glassy state does not meet the glassy features of classical spin-glass compounds.

We report the new results of exchange bias effect in Nd1−xSrxCoO3 for x = 0.20 and 0.40, where the exchange bias phenomenon is involved with the ferrimagnetic (FI) state in a spontaneously phase separated system. The zero-field cooled magnetization exhibits the FI (TF I ) and ferromagnetic (TC ) transitions at ∼ 23 and ∼ 70 K, respectively for x = 0.20. The negative horizontal and positive vertical shifts of the magnetic hysteresis loops are observed when the system is cooled through TF I in presence of a positive static magnetic field. Training effect is observed for x = 0.20, which could be interpreted by a spin configurational relaxation model. The unidirectional shifts of the hysteresis loops as a function of temperature exhibit the absence of exchange bias above TF I for x = 0.20. The analysis of the cooling field dependence of exchange bias field and magnetization indicates that the ferromagnetic (FM) clusters consist of single magnetic domain with average size around ∼ 20 and ∼ 40Å for x = 0.20 and 0.40, respectively. The sizes of the FM clusters are close to the percolation threshold for x = 0.20, which grow and coalesce to form the bigger size for x = 0.40 resulting in a weak exchange bias effect.