Study on GMR in CoAg thin granular films

A phenomenological theory of the granular size effect on the giant magnetoresistance of granular films

“…3(a), GMR decreases monotonically with increasing size of magnetic granules, while in Fig. 3(c) GMR increases monotonically with increasing size of magnetic granules, which are apparently different from experimental observations [10,27,28]. It is known from physical views that on one hand, the surface-to-volume ratio of the granules increases with decreasing particle size, giving rise to the enhancement of the spin-dependent interface scattering and GMR effect; on the other hand, when the granule size decreases to below the mean free path of electrons, the currents pass by the granules more easily, giving rise to the reduction of spin-dependent interface scattering and GMR effect.…”

“…The behaviours of GMR as a function of granular size in Fig. 3(b) at measuring temperatures 4 and 300 K were observed by many experiments [27,28] in addition to the ones in Co-Ag granular films [10], moreover, the GMR at 4 K is larger than that at 300 K in the same granular size, which indicates that single domain ferromagnetic granules play a key role in GMR effect. show the dependence of GMR effect on the volume-fraction of magnetic granules at 4 and 300 K for superparamagnetic, single domain, and multidomain magnetic granules as a key role in GMR, respectively.…”

“…Meanwhile, the smaller the granule size, the easier the granules show superparamagnetic nature, hence superparamagnetic granules show that GMR increases monotonically with decreasing granular size. However, Sang et al [10] found that there is no monotonic relationship between granule size and GMR effect, rather than the existence of a peak value at a certain size for a given temperature; furthermore, Gu et al [11] proved theoretically this phenomenon. Their explanation is that the magnetotransport in a granular system is between those in the CIP (current in the plane) case and CPP (current perpendicular to the plane) case in a multilayer, however, the magnetotransport moves from CPP case to CIP case when the granular size decreases further from the size corresponding to the maximum value of GMR, which is an opposite tendency when granular size is larger than the one corresponding to maximum value of GMR, as a result, GMR decreases rapidly with further decrease in granular size.…”

Magneto-resistance above 300K in nano-crystalline Co–Ag metastable solid solutions

“…However MR in bulk nano-crystalline Co-Ag has not been explored yet. For a sizable GMR, small particles are favorable because of the large surface/volume ratio [6][7][8][9]. The size of the particles and their separation must be smaller than the spin-dependent electron mean free path [10].…”

Effect of Granule Shape on the Giant Magnetoresistance for Ferromagnetic Metal-Metal Granular Films

“…However, it is so far conflicting about the effect of granule shape on the GMR. Sang et al found that spherical shape granules are beneficial to the GMR [10]. However, Kataoka et al indicated that granules with a pancake-like shape are advantageous to the GMR [11].…”