Magnetic signatures of ferromagnetic polarons inLa0.7Ca0.3MnO3: Colossal magnetoresistance is not a Griffiths singula

Abstract

Magnetic measurements of La 0.7 Ca 0.3 MnO 3 reveal a departure from Curie-Weiss behavior below the orthorhombic ͑O͒ to rhombohedral ͑R͒ structural transition at T O−R = 705 K. Between T O−R and T ‫ء‬ = 273 K, the magnetic response is clearly paramagnetic but with an enhanced magnetic moment attributed to the existence of small ferromagnetic polarons. These polarons grow in density and begin to interact below T ‫ء‬ as evidenced through low-field magnetic-susceptibility and field-dependent magnetization measurements, which show hysteresis and saturation, respectively. At the ferromagnetic transition temperature T c = 247.1 K, the polarons coalesce and the system exhibits long-range ferromagnetism. It is asserted that the transition at T c should be viewed as a polaronic to ferromagnetic phase transition. The relevance of the Griffiths phase is addressed.

Evidence of the Griffiths phase in multiferroic BiMnO3 and BiFe0.5Mn0.5O3 films

“…. A similar PM response with the enhanced magnetic moment has already been observed in the manganites [23] and was attributed to …”

Spontaneous magnetization aboveTCin polycrystallineLa0.7Ca0.3MnO3Turcaud1, Pereira2, Sandeman3 et al. 2014Phys. Rev. B394191View full textAdd to dashboardCite

“…In fact, Souza et al [17] referred to T * as the high-temperature limit of the range T < T C < T * where ferromagnetic polarons play a dominant role. Polarons are made of local distortions in the lattice, and as such they change the distances between magnetic ions and thus the balance of the exchange magnetic interaction.…”

“…This is the feature that is commonly referred to as the signature for "Griffiths-like" phase behavior [17,20,21].…”

“…Later Lynn et al demonstrated the existence of a polaron glass phase characterized by short-range polaron correlations, present above T C [16]. In 2008, de Souza et al [17] suggested that the Griffiths-like treatment is inappropriate and a proper description should incorporate the formation of magnetic polarons (manifest as ferromagnetic clusters organized in Mn-spin dimers [18]) coalescing over the temperature range between T * and T C . In order to shed light on the origin of the ordering temperature T * , we have performed a detailed study comparing the magnetic, electronic, and structural properties of La 0.7 Ca 0.3 MnO 3 (orthorhombic LCMO) and La 0.7 Ba 0.3 MnO 3 (rhombohedral LBMO).…”

Magnetic proximity effect in Pr0.5Ca0.5MnO3/La0.7Sr0.3MnO3 bilayered films

“…Analysis reveals that effective magnetic moment, obtained from the experimental data, eff μ [24] and was attributed to an existence of the magnetic small-size polarons, which are typical for the diluted magnetic semiconductors. In this case the expression for the effective magnetic moment can be modified:…”