Sm3+ doped spinel cobalt ferrite nanoparticles with a generic formula CoSmxFe2−xO4 (x = 0.00, 0.06, 0.12 and 0.18) were prepared using wet chemical co-precipitation technique. The structural, optical, magnetic and dielectric characteristics of the samples were investigated carefully. The phase purity and growth of spinel cubic structure was verified by room temperature x-ray diffractograms. Mean crystallite size was observed within the range of 6 nm to 15 nm as calculated from Scherrer’s formula. A blue shift in the indirect optical band gap was noticed with increasing Sm percentage as observed in UV–vis spectra due to the nanosize effect. Superparamagnetic nature at 300 K was detected for all Sm doped ferrite samples. Field cooled (150 kOe) M-H loops obtained at 5 K revealed a large amount of exchange bias field (≈4 kOe) together with high coercivity for the sample having smallest sized particles. Dielectric responses of all samples showed that the hopping of electrons was the fundamental charge conduction mechanism and grain boundaries play a crucial role in determining the dielectric properties.
The possibility of modifying the ferromagnetic response of a multiferroic heterostructure via fully optical means exploiting the photovoltaic/photostrictive properties of the ferroelectric component is an effective method for tuning the interfacial properties. In this study, the effects of 405 nm visible‐light illumination on the ferroelectric and ferromagnetic responses of (001) Pb(Mg1/3Nb2/3)O3‐0.4PbTiO3 (PMN‐PT)/Ni heterostructures are presented. By combining electrical, structural, magnetic, and spectroscopic measurements, how light illumination above the ferroelectric bandgap energy induces a photovoltaic current and the photostrictive effect reduces the coercive field of the interfacial magnetostrictive Ni layer are shown. Firstly, a light‐induced variation in the Ni orbital moment as a result of sum‐rule analysis of x‐ray magnetic circular dichroic measurements is reported. The reduction of orbital moment reveals a photogenerated strain field. The observed effect is strongly reduced when polarizing out‐of‐plane the PMN‐PT substrate, showing a highly anisotropic photostrictive contribution from the in‐plane ferroelectric domains. These results shed light on the delicate energy balance that leads to sizeable light‐induced effects in multiferroic heterostructures, while confirming the need of spectroscopy for identifying the physical origin of interface behavior.
Mn 3 Si 2 Te 6 is a rare example of a layered ferrimagnet. It has recently been shown to host a colossal angular magnetoresistance as the spin orientation is rotated from the in-to out-of-plane direction, proposed to be underpinned by a topological nodal-line degeneracy in its electronic structure. Nonetheless, the origins of its ferrimagnetic structure remain controversial, while its experimental electronic structure, and the role of correlations in shaping this, are little explored to date. Here, we combine x-ray and photoemission-based spectroscopies with first-principles calculations to probe the elemental-selective electronic structure and magnetic order in Mn 3 Si 2 Te 6 . Through these, we identify a marked Mn-Te hybridization, which weakens the electronic correlations and enhances the magnetic anisotropy. We demonstrate how this strengthens the magnetic frustration in Mn 3 Si 2 Te 6 , which is key to stabilizing its ferrimagnetic order, and find a crucial role of both exchange interactions extending beyond nearest-neighbors and antisymmetric exchange in dictating its ordering temperature. Together, our results demonstrate a powerful methodology of using experimental electronic structure probes to constrain the parameter space for first-principles calculations of magnetic materials, and through this approach, reveal a pivotal role played by covalency in stabilizing the ferrimagnetic order in Mn 3 Si 2 Te 6 .
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