Impact of reduced dimensionality on the magnetic and magnetocaloric response of La0.7Ca0.3MnO3

Abstract

Understanding the impact of reduced dimensionality on the magnetic and magnetocaloric responses of a material is vital in incorporating it as an active magnetic refrigerant in cooling devices. By contrasting the magnetic and magnetocaloric behaviors of bulk polycrystalline, sol-gel derived nanocrystalline, and pulsed laser deposited thin film forms of the La 0.7 Ca 0.3 MnO 3 system, we show that reducing the dimensionality of a ferromagnetic material tends to broaden and shift the paramagnetic to ferromagnetic transition to lower temperatures, while decreasing the saturation magnetization and the magnitude of the magnetic entropy change. Relative to its bulk counterpart, a pronounced broadening of the magnetic entropy change peak in the thin film leads to enhanced refrigerant capacity-an important figure-of-merit for active magnetic refrigeration technology. With reduced dimensionality, universal curves based on re-scaled entropy change curves tend toward collapse, indicating a weakening of the first order nature of the transition in the nanocrystalline samples and a crossover to second order in the thin film. V

Evaluation of the magnetocaloric response of nano-sized La0.7Ca0.3Mn1-xNixO3 manganites synthesized by auto-combustion method

“…29 The maximum magnetic entropy changes observed for x=0, x=0.02, x=0.07, and 0.1 compositions are 0.85, 0.77, 0.63, and 0.59 J/kg K at 1.5 T. The value of -∆S M for the undoped sample is in good agreement with that reported in Ref. 9, in which LCMO particles with mean diameters of ∼15 nm were synthesized by sol-gel method. Nevertheless, in nanocrystalline samples, the sensitive dependence of the MCE on synthesis details becomes even more evident.…”

“…Thus, differences in the -∆S M values of more than an order of magnitude can be found in the literature for similarly sized particles subject to a comparable field change. 9,30 In general, -∆S M values achieved for Ni 2+ -doped LCMO samples synthesized by auto-combustion (this work) are higher than those reported for other manganites, e.g. La 0.7 Sr 0.3 Mn 1-x Ni x O 3 , with comparable Ni-doping levels but synthesized by standard solid state reaction.…”

“…14,15 The dimensionality strongly impacts the magnetic and magnetocaloric response of LCMO. 9,16 In the present work, results of a study of the MCE on LCMO manganites, synthesized by auto-combustion method and substituted at the Mn site by Ni 2+ are presented. Auto-combustion synthesis is characterized by fast heating rates, high temperatures, and short reaction times.…”

“…7,8 Interestingly, T C can be tuned towards higher and lower temperatures by doping with different elements such as transition-metal ions. [9][10][11] Other interesting feature of LCMO is the discontinuous FM-PM transition at T C (first-order magnetic phase transition, FOMT), which is accompanied by structural changes. 12 The discontinuous phase transition can be rounded to a continuous one of a second-order magnetic phase transition (SOMT) upon doping, reduced dimensionality and external fields.…”

Magnetocaloric effect of Sr-substituted BaFeO3 in the liquid nitrogen and natural gas temperature regions

“…1,2 A considerably large MCE has been found in several systems such as Gd 5 (Si 1x Ge x ) 4 , 3 MnAs, 4 La(Fe 1x Si x ) 13 , 5,6 HoAgGa, 7 and perovskite-type Mn-oxides. 8,9 Generally, ferromagnets containing rare-earth elements with large atomic moments are advantageous because the field-induced entropy change near the Curie temperature is strongly enhanced.…”