ABSTRACT
The magnetic properties of the double perovskites Sm2Mn1+x Co1-x O6 (x = 0, 0.05, 0.12 and 0.26) were investigated. It was found that the Curie temperature, the lattice parameters and the net magnetic moments increased for increasing amounts of Co. An irreversible behavior was observed by measuring the magnetization after cooling the sample with and without applied magnetic fields (H). The temperature below which the irreversibility was observed is H dependent and the data were nicely fit to de Almeida-Thouless lines. The ac magnetic susceptibility was measured for frequencies fâ in the range 0.03-10 kHz yielding [Formula: see text] for the shifting in the freezing temperature per decade of fâ. The spin-dynamics were found to follow a power-law with a product of the critical exponents [Formula: see text] of about 4.99. The overall results are understood within a framework where the variation in the bonding angle associated to the super-exchange interactions are taken into consideration.
ABSTRACT
The use of graphene in spintronic devices depends, among other things, on its ability to convert a spin excitation into an electric charge signal, a phenomenon that requires a spin-orbit coupling (SOC). Here we report the observation of two effects that show the existence of SOC in large-area CVD grown single-layer graphene deposited on a single crystal film of the ferrimagnetic insulator yttrium iron garnet (YIG). The first is a magnetoresistance of graphene induced by the magnetic proximity effect with YIG. The second is the detection of a dc voltage along the graphene layer resulting from the conversion of the spin current generated by spin pumping from microwave driven ferromagnetic resonance into a charge current, which is attributed to the inverse Rashba-Edelstein effect.
ABSTRACT
We report experiments with polyaniline-Fe3O4 (PANI-Fe3O4) nanocomposites synthesized under several different conditions. With a reaction carried out at room temperature and assisted by intense ultra-violet (UV) irradiation, we observe sustained oscillations in the magnetization with a period of about 25 min. The oscillations are interpreted as the result of an oscillatory chemical reaction in which part of the Fe(+2) ions of magnetite, Fe3O4, are oxidized by the UV irradiation to form Fe(+3) so that a fraction of the magnetite content transforms into maghemite, γ-Fe2O3. Then, Fe(+3) ions at the nanoparticle surfaces are reduced and transformed back into Fe(+2), when acting as an oxidizing agent for polyaniline in the polymerization process. Since maghemite has smaller magnetization than magnetite, the oscillating chemical reaction results in the oscillatory magnetization. The observations are interpreted with the Lotka-Volterra nonlinear coupled equations with parameters that can be adjusted to fit very well the experimental data.
ABSTRACT
The low temperature magnetization, specific heat, electrical resistance and magnetoresistance have been studied for the Ru-doped La(1.32)Sr(1.68)Mn(2 - y)Ru(y)O(7) (y = 0.0, 0.04, 0.08 and 0.15) layered manganite system. The undoped compound (y = 0.0) shows a sharp ferromagnetic transition (T(C)) accompanied by a metal-insulator transition (T(MI)) at 118 K. The Ru substitution decreases the T(C) and T(MI) temperatures significantly. The temperature dependence of specific heat measurement confirms the decrease in T(C) by observing the anomaly corresponding to T(C). The decreased effective moments from 3.48 µ(B) for the undoped compound to 1.82 µ(B) for the highly doped compound at 5 K indicates the Ru substitution weakens the ferromagnetic order in the low temperature regime and reduces the number of Mn pairs in the highly doped sample. The field dependence of magnetization measurements exhibits an enhancement of the coercive field with increased Ru concentration and gives evidence for the mixed magnetic phase for the highly doped compound. For the undoped sample, a large negative magnetoresistance of 300% at T(C) and 128% at 4.2 K in a 5 T field were observed. The magnetoresistance ratio decreases gradually with increasing Ru substitution. We find that the doped Ru in the Mn site drives the layered manganite system towards a magnetically mixed state. The effects of Ru doping in the transport and magnetic properties will be explained by the antiferromagnetically coupled Ru and Mn sublattices.
