Magnetoresistance and nanoscopic magnetic coherence in some frustrated ferromagnets

Proximity magnetoresistance in Ag 70 Fe 30 and Ag 74 Fe 26 cosputtered granular films

“…This effect can be ascribed to the presence of a low-temperature disordered magnetic state (spin-glass like), as already observed in a Fe-FeO core-shell system [9]. A recent model relates the experimental MR(m) curves to the magnetic correlation among scatterers and to its changes with field and temperature [5]. In this frame, the absence of a significant PMR at low m values implies that the processes contributing to magnetic ordering involve the re-arrangement of regions having a spatial extension much larger than the average electronic mean free path λ.…”

“…A magnetic correlation length R, function of both applied field and temperature, can be straightforwardly derived by the model [5]. The zerofield correlation length R 0 [5] and the high-field (H = 10 kOe) magnetic susceptibility χ 10kOe of both films are reported in Fig. 4.…”

“…In this frame, the absence of a significant PMR at low m values implies that the processes contributing to magnetic ordering involve the re-arrangement of regions having a spatial extension much larger than the average electronic mean free path λ. A magnetic correlation length R, function of both applied field and temperature, can be straightforwardly derived by the model [5]. The zerofield correlation length R 0 [5] and the high-field (H = 10 kOe) magnetic susceptibility χ 10kOe of both films are reported in Fig.…”

“…This effect has been termed proximity magnetoresistance (PMR), because the magnetic scatterers are identified as adjacent regions of magnetic coherence with no diamagnetic region between scatterers [3]. Magnetoresistance and magnetisation data on magnetic nanoparticle systems may be combined to give information about magnetic correlation extending at the mfp scale [5]. However, the model has not yet been applied to nanogranular systems obtained by sputtering.…”

“…The data are exploited to get the value of the correlation length [5] among magnetic scatterers, allowing one to draw a coherent picture of these nanoscale magnetic systems.…”