Spin-wave scattering at low temperatures in manganite films

Abstract

The temperature T and magnetic field H dependence of the resistivity ρ has been measured for La0.8−ySr0.2MnO3 (y=0 and 0.128) films grown on (100) SrTiO3 substrates. The low-temperature ρ in the ferromagnetic metallic region follows well ρ(H, T ) = ρ0(H) + A(H)ωs/ sinh(hωs/2kBT ) + B(H)T 7/2 with ρ0 being the residual resistivity. We attribute the second and third term to smallpolaron and spin-wave scattering, respectively. Our analysis based on these scattering mechanisms also gives the observed difference between the metal-insulator transition temperatures of the films studied. Transport measurements in applied magnetic field further indicate that spin-wave scattering is a key transport mechanism at low temperatures. The observation of colossal magnetoresistance CMR effect in manganite films [1] has produced a resurgence of interest in these materials for both fundamental physics and their possible application in recording media and magnetic switching devices. The microscopic transport mechanism in these materials has long been thought to be double exchange DE [2,3,4]. However, it has been realized [5] that the effective carrier-spin interaction in the DE model is too weak to lead to a significant reduction of the electronic bandwidth, which would justify the observed several orders of magnitude increase in conductivity just below the Curie temperature T C . Indeed, a large number of experiments have shown that the DE scenario alone cannot account for the properties of the manganites and that CMR is not purely electronic in origin [6,7].Low-temperature charge transport measurements of manganites in the ferromagnetic metallic state are essential in clarifying the specific mechanisms responsible for the CMR effect. At low temperatures, a dominant T 2 term in resistivity has generally been observed [8,9,10]. Although the T 2 behavior is consistent with electronelectron interaction [11], the coefficient of the T 2 term is about 60 to 70 times larger than the one expected for electron-electron scattering [12]. Moreover, a careful check of the low-temperature resistivity [13,14] has shown substantial deviation from the T 2 −like behavior in the very low temperature region. Other power-law temperature dependences of the resistivity have also been reported [10,14,15,16,17,18,19]. At present, there is no agreement on the actual scattering mechanism below the Curie temperature.Here, we address the low-temperature scattering mechanism in manganites through resistivity measurements of La 0.8−y Sr 0.2 MnO 3 (y = 0 and 0.128) films grown on SrTiO 3 substrates, measured in zero field as well as applied magnetic fields up to 14 T. Our data indicate that spin-wave scattering, which gives a T 7/2 dependence in the low-temperature resistivity, is a dominant dissipation mechanism in the ferromagnetic state of these manganites, besides scattering of small polarons by a soft optical phonon mode. Our analysis of the resistivity data in terms of small-polaron and spin-wave scattering mechanisms, and the spin fluctuation model also g...

Effects of substrate-induced-strain on the structural and transport properties of La0.7Ca0.3MnO3 thin films

“…Therefore, the conduction mechanism probably corresponds to an increase in the spin-wave scattering involving the electron-magnon or two-magnon scattering. The electronic transport in the LCMO film grown on the LSAT substrate is likely dominated by scattering of spin waves, since α is nearly equal to 3.5 [15]. On the other hand, the transport in the LCMO film grown on LAO looks dominated by an increase of diffusion spin waves seeing that α = 3.74, which is slightly higher than 3.5.…”

“…Furthermore, several mechanisms have been proposed to be at work in these compounds. These contain the scattering with thermally excited magnons giving a T 3 dependence [12,14]; the T 7/2 dependence [15] would give a spin wave scattering process and the T 5 dependence would lead to an interaction with acoustic phonons [8,14]. More recently, Mercone et al [12] reported that the resistivity of manganite thin films at low temperature (T < T P ) can be well described by a T α power low.…”

Thermoelectric power of potassium doped lanthanum manganites at low temperatures

“…Twomagnon-scattering dominated electric transport has been reported for both the infinite layer materials [51] and bilayer manganites [50]. Recently, Chen et al [52] reported the existence of spin-wave scattering, contributing a T 3.5 dependence in the low temperature resistivity of thin films of lanthanum manganites. The origin of this T 3.5 dependence was proposed for a ferromagnet at low temperatures in the general theory of spin-wave interactions [53].…”

Strain dependence of the physical properties of epitaxial La0.7Ca0.3MnO3 thin films grown on LaAlO3 substrates

“…In the low temperature interval (zone II) the thinnest LCMO film (20 nm) is characterized by the largest value of a ¼ 3.34 which does not correspond exactly to any one from of the specific scattering mechanisms cited above. In fact, this value is found between 3 and 3.5 corresponding probably to the diffusion process of anomalous single magnon [25,26] and spin-wave scattering process [27], respectively. Therefore, the conduction mechanism probably corresponds to an increase in the anomalous single magnon scattering involving the spin-wave scattering.…”

“…where r 0 is the residual resistivity, A is a free fitting parameter and T a is a generic T-power law which can simulate different scattering processes such as electroneelectron (T 2 ) [23,24], anomalous single magnon (T 3 ) [25,26] and spin-wave (T 7/2 ) [27]. Fig.…”