K. De

Interparticle interaction and size effect in polymer coated magnetite nanoparticles

The value of the surface anisotropy constant Ks as obtained from equation (5) in the 11th line from the top of page 9098 should be Ks= 0.15 × 10-4 Jm-2.

Multifunctionality attributed to the self-doping in polycrystalline La0.9MnO3 : Coexistence of large magnetoresistance and magnetocaloric effect

We report the multifunctionality near room temperature attributed to the self-doping in polycrystalline La0.9MnO3. The peak in the temperature dependence of magnetoresistance (MR) and change of magnetic entropy (ΔSM) are observed at 254 K with −MR=55% at 50 kOe and −SM=4.9 J/kg K at 20 kOe where the Curie temperature and metal-insulator transition coexist at 254 K associated with a first order transition. The correlation between resistivity and ΔSM is observed in a limited region around TC. Here ΔSM is close to the largest reported values in manganites, suggesting that the material is interesting for multiple applications.

Unusual glassy states in LaMn0.5Fe0.5O3: Evidence of two distinct dynamical freezing processes

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.

Spin-glass like features in cluster-glass compounds La1−δMn0.7Fe0.3O3

The static and dynamic features of magnetization are investigated using dc magnetization and ac susceptibility measurements on La1−δMn0.7Fe0.3O3 for δ = 0 and 0.13. The results indicate that short range ferromagnetic clusters coexist with the glassy magnetic state. The analysis on the frequency dependence of spin freezing temperature (Tf) using the Vogel–Fulcher law and the dynamical scaling behaviour near Tf indicates that the spin freezing temperature behaves like a spin-glass transition temperature for both the compounds. The cluster-glass states of both the compounds exhibit similar characteristic features.

Reply to comment on 'Particle size dependent exchange bias and cluster-glass states in LaMn0.7Fe0.3O3 '

In reply to the comment by Geshev we emphasize that loop shift in the compounds is not a simplified phenomenon of minor loop effect of a ferromagnet rather, it is a genuine signature of exchange bias effect. The estimate of anisotropy field and the plot of exchange bias field at 5 K with the maximum field used for the measurement of hysteresis loop, in addition to the previously reported results such as temperature dependence of exchange bias field, training effect, etc, confirm the exchange bias effect.

Particle size dependent exchange bias and cluster-glass states in LaMn0.7Fe0.3O3

The cluster-glass compound LaMn0.7Fe0.3O3 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.

Inhomogeneous phase separation and domain wall dynamics in orthorhombically distorted La0.87MnOx

We observe interesting magnetization and resistivity results in the orthorhombically distorted self-doped manganite, La0.87MnOx. A significant irreversibility between zero-field-cooled and field-cooled resistivities as well as magnetization data is clearly observed up to a temperature which is well above the both paramagnetic to ferromagnetic (Tc) and metal to insulator (TMI) transition temperatures. In the ferromagnetically ordered and metallic states the magnetotransport results suggest the influence of domain wall dynamics. An interesting scenario of memory effects through the domain wall dynamics is strikingly observed in the relaxation of resistivity in a limited temperature region. The characteristic features of magnetotransport behaviour are suggested to be due to the coexistence of structurally driven inhomogeneous phase separation and domain wall dynamics.

Magnetic and electrical transport properties of La0.87Mn1−xFexO3 (0 ⩽ x ⩽ 0.15): coexistence of ferromagnetic and glassy magnetic states

We report on the effect of Fe substitution in the self doped manganite, La0.87Mn1−xFexO3 in the composition range 0 ≤ x ≤ 0.15. The electrical resistivity (ρ) and dc magnetization were measured as a function of temperature, field and time. The metal to semiconducting transition is clearly observed for x ≤ 0.02, while a semiconducting temperature dependence of resistivity is noticed for x ≥ 0.08. The compound with x = 0.05 shows interesting features of ρ in field-cooled (FC) condition such as bifurcation in the zero-field cooled and FC temperature dependence, weak thermal hysteresis and memory effect. We observe the enhancement of colossal magnetoresistance by the Fe substitution in the low substitution range. The paramagnetic to ferromagnetic transition (Tc) is found to decrease with increasing x. The large thermal hysteresis in magnetization under FC condition is noticed for x ≤ 0.02, which is different in character for the composition range 0.05 ≤ x ≤ 0.15. The relaxation of magnetization indicates the ferromagnetic (FM) character for x = 0, while the coexistence of FM and glassy components is observed for x ≥ 0.02. The glassy magnetic phase increases with the increase in Fe substitution. The inhomogeneous phase separation between FM and glassy magnetic phases has been proposed to explain the magnetic and electrical transport properties of La0.87Mn1−xFexO3.

Spin polarized tunneling magnetoresistance in the self-doped manganite La0.9MnO3

We observe the tunneling magnetoresistance (TMR) at low temperature (T) and low field attributed to the self-doping in polycrystalline La0.9MnO3. The occurrence of TMR is suggested due to the tunneling through the grain boundary (GB) region. Tunneling component of the magnetoresistance ascribed to the disordered magnetic GB region follows the Curie–Weiss-like T dependence. The nonlinear current-voltage curves at low T indicate that the inelastic tunneling via localized states involved with the GB effect is dominant where at low temperature the number of inelastic channels and the fraction of charge carriers entering in each inelastic channel change with temperature.

Memory effect and inverse thermal hysteresis in La0.87Mn0.98Fe0.02Ox

We have investigated electrical transport and magnetization studies as a function of temperature, magnetic field, and time for polycrystalline La0.87Mn0.98Fe0.02Ox. The temperature dependence of resistivity exhibits a bifurcation in the zero-field cooled and field-cooled behavior below the paramagnetic to ferromagnetic transition temperature (Tc≈205 K). We observe an inverse thermal hysteresis in field-cooled resistivity in the temperature range of 85–200 K. Similar thermal hysteresis in the field-cooled magnetization is also observed. In consistence with the thermal hysteresis, the relaxation of magnetization exhibits the different magnetic characteristics in the heating and cooling cycles. The sample shows interesting memory effect in the relaxation of field-cooled resistivity. The magnetoresistance and magnetization studies suggest that the above unusual features are ascribed to the inhomogeneous structural phase separation in the case of minor Fe substitution.