Charge ordered ferromagnetic phase in La0.5Ca0.5MnO3

TL;DR

This study reveals the coexistence of charge ordered and ferromagnetic phases in La0.5Ca0.5MnO3, uncovering a novel phase with regions of both charge order and ferromagnetism using advanced electron microscopy techniques.

Contribution

The paper provides direct electron microscopy evidence of coexisting charge order and ferromagnetism in La0.5Ca0.5MnO3, revealing a previously unknown phase.

Findings

Ferromagnetic regions have a local magnetisation of 3.4 mB/Mn.

Charge order exists in both magnetized and non-magnetized regions.

Coexistence of charge order and ferromagnetism in micron-sized regions.

Abstract

Mixed valent manganites are noted for their unusual magnetic,electronic and structural phase transitions. The La1-xCaxMnO3 phase diagram shows that below transition temperatures in the range 100-260 K, compounds with 0.2 < x < 0.5 are ferromagnetic and metallic whereas those with 0.5 < x < 0.9 are antiferromagnetic and charge ordered. In a narrow region around x = 0.5, these totally dissimilar states are thought to coexist. Uehara et al. have shown that charge order and charge disorder can coexist in the related compound La0.25Pr0.375Ca0.375MnO3. Here, we present electron microscopy data for La0.5Ca0.5MnO3 that sheds light on the distribution of coexisting phases and uncovers a novel and unexpected phase. Using electron holography and Fresnel imaging, we find micron sized ferromagnetic regions spanning several grains coexisting with similar sized regions with no local magnetisation. Holography shows that the ferromagnetic regions have a local magnetisation of 3.4 +- 0.2 mB/Mn (the spin aligned value is 3.5 mB/Mn). We use electron diffraction and dark field imaging to show that charge order exists in regions with no net magnetisation and, surprisingly, can also occur in ferromagnetic regions.