Giant magnetoresistance and superparamagnetic grains in Co–Ag granular films

Abstract

Co-Ag granular films having various Co grain sizes are prepared by rf sputtering under various sputtering conditions. The Co grain sizes are derived from the magnetization curves by dividing them into ferromagnetic and superparamagnetic components. As the Co content decreases, the radii of the superparamagnetic Co grains, r g , decrease and the distances between the Co grains, t g , increase. The magnetoresistance is proportional to the volume density of superparamagnetic grains or related to kr g 3 exp(Ϫt g /l) with kϭ3.8ϫ10 2 ⍀/cm 2 and lϭ20 Å, implying that the giant magnetoresistance is caused by the spin-dependent scattering in the inner part of the superparamagnetic Co grains as well as at the grain surfaces. Furthermore, it is found that the extraordinary Hall effect arises mainly from the side jump mechanism, and that significant perpendicular magnetic anisotropy appears in the Co composition range between 40 and 70 at %.

Magnetic properties of nanoclusters formed by implantation of Fe into Ge using a metal-vapor vacuum arc ion source

“…The magnetic properties of nanocrystalline Fe-Ge alloys and the change in magnetic properties upon annealing, and their correlation to changes in the structure of the materials have been studied in detail by Hamdeh et al 18 Most of the Fe-Ge amorphous alloys were prepared by the sputter deposition method. [12][13][14][15][16][17] In this work, we report the synthesis of Fe clusters in Ge ͑110͒ by ion implantation. We report the results of magnetization and magnetoresistance measurements.…”

“…[13][14][15] There has been a lot of effort to understand the metal-insulator transition as well as the magnetic transition in the amorphous Fe-Ge system. [12][13][14][15][16][17] The magnetic properties of nanophase materials can be tuned from soft to hard, depending on the magnetic coupling between their small crystallites. The magnetic properties of nanocrystalline Fe-Ge alloys and the change in magnetic properties upon annealing, and their correlation to changes in the structure of the materials have been studied in detail by Hamdeh et al 18 Most of the Fe-Ge amorphous alloys were prepared by the sputter deposition method.…”

Nanogranular GMR Ag<SUB>72</SUB>Co<SUB>28</SUB> Thin Films for Rotating Angle Sensor at High Temperatures

“…The Ag 72 Co 28 film with a decreased MR ratio at room temperature was prepared in 6.7 × 10 −3 Pa Ar pressure because the MR ratio is mainly connected with the deposition condition. 11) Since the GMR effect is isotoropic, it is not able to distinguish the polarity of magnetic field. By using a bias magnetic field, however, the nanogranular Ag 72 Co 28 film sensor can distinguish the polarity of magnets in the rotor.…”

Giant magnetoresistive coatings using thermionic vacuum arc technology

“…However, there are numerous reports that for many practical systems such a law is not fulfilled in the range of medium and high applied magnetic fields. In fact the experimental data point to the complexity of this phenomenon in the real systems and show that the origin of the spin-dependent scattering mechanism remains still uncertain in many aspects [4].…”