Suppression of Metamagnetic Transitions of Martensitic Type by Particle Size Reduction in Charge-Ordered La_0.5Ca_0.5MnO₃

Abstract

In this paper, we have studied the effect of size reduction on charge ordering (CO) and magnetic phase separation in La 0.5 Ca 0.5 MnO 3 . The magnetic ground state at low temperature shifts from ferromagnetic (nanoparticles) to CO-antiferromagnetic (bulk) with increasing annealing temperature. The studied samples exhibit relevant phenomena such as Griffiths phase and training effect. Magnetic field cycling can stabilize ferromagnetic or antiferromagnetic domains, depending on the temperature value as well as the sample's nature. For the compound sintered at 1200 °C, step-like metamagnetic transitions of martensitic type were observed at 4 K, indicating the presence of weak spin-phonon coupling. The disappearance of magnetic phase separation at 4 K (the sample is purely antiferromagnetic) can be a possible origin for the occurrence of such transitions. Lowering the sintering temperature leads to the disappearance of martensitic transitions. The obtained results indicate that the occurrence of step-like metamagnetic transition of martensitic type necessarily requires the onset of a long-range CO-antiferromagnetic state.

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.…”

La0.6X0.1Te0.3MnO3 system with significant refrigerant capacity at low magnetic field and double magnetic entropy change peaks: effect of ball-milling time on physical and critical behaviors

“…Besides, both ZFC and FC curves exhibit the appearance of a maximum at around T max . This can be attributed to the presence of superparamagnetism (SPM) or spin-glass-like state (SG) [26]. It can also be explained by the ferrimagnetic transition of Mn 3 O 4 (also seen in XRD) at about 50 K.…”

“…Furthermore, the bright difference between ZFC and FC plots in all the samples denotes that the magnetic state is inhomogeneous. This act can be attributed to a SG behavior; noting that it can also be associated to a chemical disorder upon the ball-milling process [26,27]. Figure 7(b) shows the evolution of the first derivative of FC plots versus the temperature for the three samples.…”

Strain-induced charge ordering above room temperature in rare-earth manganites

“…10,19,35,36 This explains why the CO state is not observed in the case of the manganite nanoparticles. 37–39 Thus, the key to the appearance of the high-temperature martensitic CO state in the studied films lies in the crystallite size and the boundary between them. The absence of the CO phase in the 110 nm-thick LSMO film is probably due to its less defective crystal structure.…”