Charge-order breaking and ferromagnetism in La0.4Ca0.6MnO3 nanoparticles

Abstract

La 0.4 Ca 0.6 MnO 3 nanoparticles of grain size as small as ϳ20 nm are prepared and their magnetic behaviors are investigated in order to understand the size effect of the charge ordering in manganites. The highly stable charge-ordered state can be significantly suppressed upon reduction of the grain size down to nanometer scale, while the ferromagnetism is enhanced. The magnetic phase separation due to the competition between ferromagnetic state and charge-ordered state as well as the surface spin disordering is responsible for the spin-glass-like state at low temperature.

Impact of nanostructuring on the magnetic and magnetocaloric properties of microscale phase-separated La5/8−yPryCaBingham1, Lampen2, Phan3 et al. 2012Phys. Rev. B

“…We note that these studies of grain size reduction in polycrystalline LPCMO have not crossed the ~100nm threshold, below which surface effects dominate the physics of manganite nanoparticles. 43 With the exception of our previous study on a closely related composition, 10 we find that despite wealth of available literature on thin films, [29][30][31][32][33][34][35][36][37]41 single- 19,22,25,26,28,40 and polycrystalline 8,9,14,17,18,20,21,23,24,45 forms of LPCMO, virtually no work has been done on nanoparticles of the same compounds, although reduction of particle size to well below the characteristic phase separation length can be expected to have a great impact on strain, and consequently on the magnetic properties of the system. 10 Adding an additional layer of interest, opposing surface-driven trends are observed in nanosized FM and CO compounds.…”

“…43,44 This collapse of CO on the nanoscale is a particularly well-documented phenomenon in manganites, and has been observed in both materials with a single phase in the bulk form and those with two coexisting phases. [45][46][47][48][55][56][57] The presence of a third phase in LPCMO -the charge-disordered PM phase discussed above -lends a unique aspect to the study of nanoparticles of this compound as the impact of size reduction on the interplay of these three phases is not immediately obvious based on previous results.…”

Martensite-like transition and spin-glass behavior in nanocrystalline Pr0.5Ca0.5MnO3

“…Among the notable findings, weakening of the CO phase and the appearance of a FM phase were reported on several manganites of various CO strengths, though the origin of such particular phenomenon is still under intense debate. [5][6][7][8][9][10] To quote from archival knowledge [5][6][7][8][9][10] in explaining such an effect, several groups argued that surface disorder and structural changes upon size reduction could be the main origin. To provide further insights in explaining such puzzling experimental observations, Dong 11 theoretically based on a two-orbital double exchange model near half (0.5) doping using Monte Carlo techniques, concluding that an 'unexpected surface phase separation' could be responsible for the appearance of the weak FM.…”

“…Also the crucial role of size induced disorder needs further exploration. Though a weak FM phase is introduced upon size reduction in such materials, [5][6][7][8][9][10] the 'global FM' state is not achieved, yet an important criterion for spin based applications. Recently, there was a suggestion 15 stating that it is possible to induce a global FM phase by external magnetic fields.…”

“…Intense research efforts have been made [5][6][7][8][9][10] to investigate the physics of nanoscale CO manganites to explore possible applications. Among the notable findings, weakening of the CO phase and the appearance of a FM phase were reported on several manganites of various CO strengths, though the origin of such particular phenomenon is still under intense debate.…”