Exchange interaction and magnetoresistance in La2/3Ca1/3MnO3: experiment and models

Abstract

The magnetization M(T) and electrical resistivity r(T) of a La Ca MnO 2 13 3 3 film have been studied in the temperature range 5 K £ T £ 320 K in the magnetic field intervals 10 Oe £ H £ 400 Oe and 0 £ H £ 50 kOe, respectively. It is found that the M(T)/M(0) value is larger than that predicted by the conventional molecular field model below the Curie point T = 267 K, and that the ln r(T) dependence is close to linear in the temperature range 80 K < T < 200 K (accordingly, ¶ ln r/ ¶T is constant in this region). A model of the electrical conductivity and magnetoresistivity of the system describing qualitatively the experimental results is proposed (the Dmt model). The model includes a thermally activated (with characteristic energy D) mechanism of conductivity, dependence of the concentration and the effective mass (m) of the itinerant charge carriers on the magnetization, as well as scattering (with characteristic time t) of the charge carriers by static breakings of the translational symmetry, thermal fluctuations of the magnetic order, and phonons.

Magnetic behaviour of synthetic Co2SiO4

“…To compensate for this discrepancy, a modified molecularfield model (Beznosov et al, 2002) was applied, which differs from the conventional form by the additional fitting parameters h and a…”

“…where h is a fictive magnetic-field modeling the effect of shortrange magnetic order above T N and a is a magnetoelastic parameter describing the magnetostrictive shift of T N (Beznosov et al, 2002;Fertman et al, 2001). Note that the magnetic anisotropy found in Co 2 SiO 4 according to the magnetic susceptibility measurements (x3.…”

Giant radio-frequency magnetoabsorption effect in the cobaltite ceramic La0.5Sr0.5CoO3

“…The magnetoresistance (MR) in manganites, defined as δ(H) = [R(0) − R(H)]/R(0), is found to be more than 90 % at a field H of about 60 kOe in the neighbourhood of room temperature. In spite of enormous efforts, a clear understanding of CMR is not yet available, though some models describe experimental data with an acceptable accuracy [6,7,8]. Beside this, the requirement of high magnetic fields hampers the possible application of the CMR manganites.…”

Evolution of two-dimensional antiferromagnetism with temperature and magnetic field in multiferroicBa2CoGe2O7

“…We analyzed the data in a modified molecular field model [39] where h is a fictive magnetic field modeling the effect of shortrange magnetic order above T N , and a is a magnetoelastic parameter describing the magnetostrictive shift of T N (Refs. [39] and [40]).…”