Nanoclustering phase competition induces the resistivity hump in colossal magnetoresistive manganites

Abstract

Using a two-band double-exchange model with Jahn-Teller lattice distortions and super-exchange interactions, supplemented by quenched disorder, at electron density n = 0.65, we explicitly demonstrate the coexistence of the n = 1/2-type (π, π) charge-ordered and the ferromagnetic nanoclusters above the ferromagnetic transition temperature Tc in colossal magnetoresistive (CMR) manganites. The resistivity increases due to the enhancement of the volume fraction of the charge-ordered and the ferromagnetic nanoclusters with decreasing the temperature down to Tc. The ferromagnetic nanoclusters start to grow and merge, and the volume fraction of the charge-ordered nanoclusters decreases below Tc, leading to the sharp drop in the resistivity. By applying a small external magnetic field h, we show that the resistivity above Tc increases, as compared with the case when h = 0, a fact which further confirms the coexistence of the charge-ordered and the ferromagnetic nanoclusters. In addition, we show that the volume fraction of the charge-ordered nanoclusters decreases with increasing the bandwidth and consequently the resistivity hump diminishes for large bandwidth manganites, in good qualitative agreement with experiments. The obtained insights from our calculations provide a complete pathway to understand the phase competition in CMR manganites.

Huge magnetoresistance and ultrasharp metamagnetic transition in polycrystalline Sm0.5Ca0.25Sr0.25MnO3

“…In this section we discuss the physical origin of the huge magnetoresistance using a two-band double exchange model including super-exchange (J) and electronphonon coupling (λ). Our model Hamiltonian 19,[47][48][49][50] (see Supplementary Section II for details), effectively a lattice of Mn ions, qualitatively reproduces the phase diagram of manganites. For SCMO (and SSMO) like materials, involving two A-type elements 30 , one generally add i i n i such that j = 0 to model the A-site cationic disorder 47,50 .…”

“…Our model Hamiltonian 19,47-50 (see Supplementary Section II for details), effectively a lattice of Mn ions, qualitatively reproduces the phase diagram of manganites. For SCMO (and SSMO) like materials, involving two A-type elements 30 , one generally add i i n i such that j = 0 to model the A-site cationic disorder 47,50 . Considering the fact that the Sr 2+ ions occupy randomly in the A-site in the polycrystalline SC-SMO compound and being larger in size compared with both Sm 3+ and Ca 2+ creates chemical disorder.…”

“…For clarity we use ∆/t = 0 (due to the small mismatch between Sm and Ca ionic radii) and set λ/t= 1.73, J/t = 0.105 for SCMO-like materials. For SSMO-like materials we set binary disorder 47,50 with ∆/t= 0.3 and use λ/t= 1.57, J/t = 0.095. The FM correlations at low temperatures increases and the resistivity decreases from SCMO-like to SCSMO-like to SSMO-like materials [Fig.…”

Designing multi-level resistance states for multi-bit storage using half doped manganites

“…In addition, antiferromagnetic superexchange interaction J between neighboring core Mn spins is taken in to account. This well investigated Hamiltonian in the double exchange limit [31] reproduces the phase diagram of manganites [32][33][34]. In SCSMO, Sr 2+ ions (larger in size as compared to Sm 3+ and Ca 2+ ions) occupy the A-sites randomly and creates chemical disorder.…”

Antiferromagnetism beyond classical percolation threshold in the site-diluted half-filled one-band Hubbard model in three dimensions

“…Temperature is lowered in small steps to allow for equilibration. To avoid size limitation we employ above mentioned Monte-Carlo technique within a traveling cluster approximation [29][30][31] to handle system size N = L 3 = 10 3 .…”