• R Nirmala

      Articles written in Pramana – Journal of Physics

    • The effect of spin dilution on magnetism of the linear chain system 𝛽-Cu$_{2−x}$Zn$_{x}$V2O7

      S N Bhatia Niharika Mohapatra R Nirmala S K Malik

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      We have measured the magnetic susceptibility (𝜒) and heat capacity ($C_{p}$) of 𝛽-Cu$_{2−x}$Zn$_{x}$V2O7 ($x$ = 0, 0.05, 0.1, 0.15, 0.2, 0.3, 2) in the temperature range 2–300 K. A one-dimensional alternating exchange Heisenberg antiferromagnetism (HAF) is observed in all compositions with chains of infinite length. The intra-chain exchange remains uniform and decreases marginally with dilution of the magnetic state. A cooperative ordering is seen in the magnetic chains for all Zn concentrations ($x \leq 0.3$). The temperature of occurrence of this transition decreases with increasing Zn concentration. Though the conventional spin-wave theory has been used here to describe the properties of the ordered phase, the presence of some contributions like the lattice heat capacity in $C_{p}$ and the Curie–Weiss term in susceptibility introduces some uncertainties in the estimation of the proportions contributed by the spin system. Therefore, the nature of the ordered phase could not be ascertained unambiguously.

    • Magnetocaloric effect in rare-earth intermetallics: Recent trends

      R Nirmala A V Morozkin S K Malik

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      Magnetocaloric effect (MCE) is the change in isothermal magnetic entropy (𝛥𝑆m)and adiabatic temperature (𝛥𝑇ad) that accompany magnetic transitions in materials during the application or the removal of magnetic field under adiabatic conditions. The physics of MCE gets enriched by correlated spin-lattice degrees of freedom. This phenomenon has been actively investigated over the past few decades as it holds a promise for an alternate method of refrigeration/heat pumping. This has already resulted in several reviews on this topic. This paper focusses on some recent trends in this field and prospects of using rare-earth-based materials as active magnetic refrigerants over a broad temperature range that includes gas liquefaction and near-room temperature refrigeration/heating.

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