Is History a Threat? (Comment)

Erick Hobsbawm (d.2012) was a Marxist historian, a professor of history at Birkbeck College, University of London, where he taught till the end of his life. Birkbeck is an evening college where most of the students belong to the working class and continue with studies to improve their educational qualifications. Conscious of the condition of students who attended his lectures after a hard day of physical labour, he devised lectures on the history of Europe to create emancipatory thought. His four books use history as a tool to comprehend present-day Europe. They are titled The Age of Capital, The Age of Industrial Revolution, The Age of Revolution and The Age of Extreme. Besides these four books, he has published a number of papers and essays that attempt to build a new historical consciousness. There are other progressive historians besides Hobsbawm who believe that history can be liberating if it is not written in the service of the rulers of the time. It is also not a static and depressing account of the past but is dynamic and constantly changing. While history tells the story of unjust rulers and the institutions they created, it also reveals how the rulers and their unjust institutions meet their end. The reign of absolute kingship where the king was considered the Viceregal God, brutal military dictatorships, and exploitative economic systems that lasted for centuries with the aim of torturing and subduing the common working people were all destroyed over time, especially when people joined forces and resisted them to gradually establish a just order.

Synthesis and Characterization of Rare Earth Doped Multiferroics Nanomaterials

The growing concern about the development of new functional nanomaterials, owing to their unique properties and tremendous potential in device applications is quite a challenge. However, the synthesis of a material having ferroelectric and ferromagnetic properties in the same phase is an interesting task. The work presented in this thesis describes the synthesis and characterization of rare earth doped multiferroic nanomaterials. Three series of Gd–Cu, Co-Ni and Nd-Mn substituted multiferroics prepared by sol gel technique have been investigated thoroughly.All the samples under study are characterized by X-ray Diffraction, Scanning Electron Microscopy, Resistivity, Dielectric Measurement and Vibrating Sample Magnetometery. The indexing of each X-ray diffraction pattern reveals the formation of well-defined orthorhombic single phase structure of all the investigated materials has been prepared. Enhancement in the intensity of peaks shows improved crystallinity suggesting that the dopants in the nominated substitution range are entirely dissolved in the lattice. Average crystallite size measured by Scherrer formula lies in the range of 23-61 nm ±2 nm for the substituted multiferroic samples. Lattice parameter changes linearly in accordance with the ionic radius of the substituted cations into the parent crystal lattice obeying the Vegard’s rule. The surface morphologies of the samples were investigated by FE-SEM analysis. All the samples have good crystalline shape and distinct boundaries of the grains that make them useful for microwave device applications. The DC electrical resistivity increases drastically from 107-1010 Ω-cm with increasing the concentration of dopants Gd-Cu, Co-Ni and Nd-Mn into the host lattice of multiferroics. The conduction in these materials is due to hopping of electrons between ferric and ferrous ions at the octahedral site. As the concentration of substituents increase, it results in the decrease of iron content at the octahedral site. As a result, the hopping of electrons decrease and consequently the resistivity is enhanced. The variation of activation energy is in agreement with the variation of room temperature resistivity for all the investigated samples. The temperature dependent dc resistivity decreases for all the samples indicating semi-conducting behavior. Dielectric properties generally follow Maxwell Wagner model and Koops phenomenological theory. The dielectric constant, complex dielectric constant and loss tangent decreases with the increase of doping concentration. Dielectric constant for Gd-Cu, Co-Ni and Nd-Mn substituted nano-materials were found to decrease in the range of 41-5.5, 41-6, and 41-10 at 1MHz respectively. The results are consistent with resistivity of the samples under investigation. The enhancement in resistivity and low dielectric loss make these materials pre-eminent contestant for multi-layer capacitor (MLC) applications. The resonance peaks in tan δ(f)are observedwhenthe external electric field matcheswith the hopping frequency of charge carriers. Electrical modulus describes the dielectric relaxation behavior for all the substituted nano-materials. The cole-cole plots show the semicircle for most of the samples to elaborate the grain and grain boundary contribution towards the dielectric relaxation phenomena. It is observed that substitution makes comparatively smaller difference on the grain resistance, but leads to a remarkable rise of grain boundary resistance. The AC conductivity increases with increasing frequency of the applied field for all the investigated samples. The frequency dependent AC conductivity follows power law with large value of exponent, n that shows the polaron hopping is the likely conduction mechanism. The magnetic properties of the Gd–Cu, Co-Ni and Nd-Mn substituted samples have been investigated from hysteresis loops. The saturation magnetization, remanence and coercivity are measured at room temperature. The saturation magnetization decreases for Gd-Cu and Co-Ni substitutions while increases for Nd-Mn dopants from 34-70 emu/g for the three substituted multiferroic series. The coercivity increases from 473-1992Oe, 190-2000 Oe for Gd-Cu and Co-Ni substituted samples, respectively. The variation of coercivity may be due to increase in the hindrance to the domain wall pinning at the grain boundaries and other defects like porosity while coercivity decreases from 705-262 Oe for the Nd-Mn substituted series. The decrease in coercivity is due to the increase in the average particle size of the materials or may be due to decrease in anisotropy constant with the Nd–Mn contents. The highest value of coercivity (~2072 Oe) ensures the use of present samples for applications in perpendicular recording media (PRM).