Phase diagram and anomalous properties of La0.7M0.3MnO3 lanthanum manganites near the structural phase transition

Abstract

The La0.7Ca0.3−xBaxMnO3 (x=0; 0.03; 0.06…0.3) and La0.7Ca0.3−xSrxMnO3 (x=0.105, 0.12, 0.135, 0.15, 0.165, and 0.18) lanthanum manganites were synthesized and studied. The Curie temperature TC of Ba range showed a sharp change near the concentration structural orthorhombic–rhombohedral phase transition. The TC values for that range are under the “classical” ferromagnetic–paramagnetic line. The TC temperatures of Sr range of samples are independent on x value at the vicinity of structural transition in the rhombohedral phase. Temperature dependence of magnetization of the La0.7Ca0.165Sr0.135MnO3 composition looks like a two-step curve which is caused by the closeness of ferromagnetic ordering and structural phase transition temperatures.

Magnetic phase diagram and structural separation of La0.7(Ca1−ySry)0.3MnO3 thin films

“…It worth noting, that the similar two-step M͑T͒ behavior recently was observed in a single crystal at y = 0.45 and explained by an occurrence of the structural transition at a temperature below T C . 16 The microstructural analysis for y = 0.5 of a composite film, however, involves two kinds of the nanoscale clusters with a different crystal lattice. It is reasonable to suggest that the two-stage M͑T͒ dependence should be a simple superposition of two separated FM transitions in clusters with the rhombohedral and orthorhombic structure.…”

“…12 The main reason for this effect is that La 0.7 ͑Ca 1−y Sr y ͒ 0.3 MnO 3 tends to experience a structural transition from the rhombohedral ͑R3c͒ to the orthorhombic ͑Pnma͒ crystal lattice with a decreasing temperature near y Ӎ 0.5. [13][14][15][16] Moreover, this transition is controlled by an external magnetic field, indicating a small difference between the ground state energies for these crystal symmetries. 15 Therefore, it is reasonable to suggest that any external perturbation of the crystal lattice ͑such as lattice strain, for example͒ leads to a structural modification in this compound.…”

Magnetic and electronic phase separation driven by structural clustering in La0.7(Ca1−ySry)0.3MnO3 thin films

“…Analysis reveals that this film has mainly a rhombohedral crystal structure with a R ; 0.5524 nm and a R ; 60.46°, which are coincident with the bulk [15]. [16]. However, according to the microstructural analysis for y = 0.5, in our case we are dealing with a composite film which involves two kinds of nanoscale clusters with a different crystal lattice.…”

“…MnO 3 to the structural transition from the rhombohedral (R c 3 ) to orthorhombic (Pnma) crystal lattice with decreasing temperature near y ; 0.5 [13][14][15][16][17]. Moreover, this transition is controlled by an external magnetic field, indicating a small difference between the ground state energies for these crystal symmetries [15].…”

Magnetoresistive Properties of Manganite-Based Heterojunctions

“…However, increasing attention is attributed also to heterojunctions based on p-type manganite films grown on conductive substrates such as n-type Nb-doped SrTiO 3 [1][2][3][4][5][6]. Significant magnetic field effect on both interface resistance and I-U characteristics of the heterojunctions could be promising for the fabrication of magnetic field sensor arrays.…”