Emissivity — a remote sensor of giant magnetoresistance

Abstract

A new experimental design for noncontact giant magnetoresistance measurements using the magnetorefractive effect Rev.The link between emissivity in the mid-to-far-infrared regime and electrical conductivity is used to probe magnetoresistance. A direct relationship between the change in radiated flux and giant magnetoresistance is confirmed by experiment. The potential for spatially resolved measurements is also considered.

Modelling the magnetorefractive effect in giant magnetoresistive granular and layered materials

“…The potential of the MRE to study magnetic thin films has previously been demonstrated. Following its first discovery using Ni 80 Fe 20 /Cu/Co/Cu multilayers in transmission experiments [1], infrared-wavelength MRE measurements have been extended to the reflection geometry [4,5], contributions to the effect from interband transitions [6] and phonon modes have been identified [7], and MRE results compared to magnetic-linear-dichroism and emissivity studies [8,9]. The wide applicability has been demonstrated in studies of the transport properties of GMR granular [5,10], multilayer [11], spin-valve [8,12] thin films, LaSrMnO perovskites [13] and granular metal-insulator systems [14][15][16].…”

Infrared emission imaging as a tool for characterization of hydrogen storage materials

“…Thus emissivity is expected to increase with the increase of hydrogen in a material. The link between emissivity in the midto-far-infrared regime and electrical conductivity was previously exploited to probe magnetoresistance [37]; a direct relationship between the change in radiated flux and giant magnetoresistance was confirmed experimentally.…”

Modelling the sensitivity of infrared emissivity of magnetic thin films to giant magnetoresistance

“…More recently, emissivity has been demonstrated experimentally as an alternative remote sensor of GMR which offers a more direct and sensitive probe of magnetotransport [6]; infact, a change in emissivity is predicted to be directly proportional to GMR. Emissivity is an emission characteristic of a material defined as the efficiency with which a material radiates energy compared to that of a perfectly radiating black body at the same temperature.…”

“…Also, no consideration has yet been made of the thin-film nature of the magnetic materials being investigated, and this is addressed here by adapting a thin-film model of emissivity by Pigeat et al [10]. It is used to directly model the link between emissivity and GMR as a function of film thickness at far IR wavelengths, and is compared to the bulk-material results used in previous studies [6][7][8][9]. The spectral dependence of the emissivity effect at mid-to-far IR wavelengths is also examined using a Drude-type model of refractive index combined with the thin-film emissivity model, and an analytic interpretation at far IR wavelengths is presented.…”

“…Understanding the relation between emissivity and GMR has so far been limited to models that obtain the emissivity indirectly from reflectivity expressions, utilising Kirchoff's second law of radiation and the conservation of energy [6]. However, a more indepth treatment of emissivity is obtained by consideration of the spontaneous emission process itself.…”