Grain size modification in the magnetocaloric and non-magnetocaloric transitions in La0.5Ca0.5MnO3 probed by direct and indirect methods

Abstract

Abstract.The influence of the grain size in the magnetic properties of phase separated manganites is an important issue evidenced more than a decade ago. The formation of long range ordered phases is suppressed as the grain size decreases giving place to a metastable state instead of the ground state. In this work we present a study of the magnetocaloric effect in the prototypical manganite La 0.5 Ca 0.5 MnO 3 as function of the grain size. The differences obtained using direct and indirect methods are discussed in the framework of domain walls in the ferromagnetic phase of the system.

Grain-Size-Induced Collapse of Variable Range Hopping and Promotion of Ferromagnetism in Manganite La0.5Ca0.5MnO3

“…To further explore these ideas, here we conduct a dc transport and magnetization study on polycrystalline (ceramic) La 1−x Ca x MnO 3 samples, where the level of structural disorder can be controlled by the grain size. We focus on the very boundary between the FM metallic and CO/AFM insulating phases x = 0.5, where the grain size is known to have a large impact on the stability of the CO/AFM phase [46][47][48][49][50][51][52]. Our results show the presence of the 3D VRH in accordance with the thin film study [45] and the coexistence of both FM and CO/AFM phases.…”

“…Interestingly, the disappearance of the VRH with reducing the grain size is accompanied by the strong suppression of the CO/AFM phase (Figures 4b and 5a), implying a close relationship between them (see Section 4 for discussion). The suppression of the CO/AFM state with reducing the grain size has been well documented in the literature for the half-doped La 0.5 Ca 0.5 MnO 3 studied here [46][47][48][49][50][51][52], as well as for some other dopings such as La 0.4 Ca 0.6 MnO 3 [61,62] and La 0.25 Ca 0.75 MnO 3 [63] and other compositions such as Pr 0.5 Ca 0.5 MnO 3 [64,65] and Nd 0.5 Ca 0.5 MnO 3 [66]. Such behavior has been ascribed to surface effects at the grain boundaries, which destabilize the bulk long-range CO/AFM order and which become progressively more pronounced with the increase of the surface to volume ratio caused by the reduction in the grain size.…”

“…Motivated by our previous study [45], which pointed towards the Anderson localization of conducting e g electrons, here we explore the sensitivity of transport and magnetic properties in La 1−x Ca x MnO 3 to the level of structural disorder controlled by the grain size. We focused on the very boundary between the FM metallic and CO/AFM insulating phases x = 0.5, where the grain size is known to strongly affect the stability of the CO/AFM phase [46][47][48][49][50][51][52]. Indeed, drastic changes in dc resistivity and magnetization were observed with varying the grain size, explained in detail in the previous sections.…”

Strange critical behaviors of ferromagnetic to paramagnetic transition in La0.5Ca0.5MnO3 nanowires bundles

“…10a is much lower than those in bulk materials. 51 The magnetic entropy is dened by the ordering degree of magnetic moments under external magnetic eld. The magnetic entropy change |DS| is known to increase monotonically with magnetic eld strengthening.…”