Abstract
Obtaining highly sensitive ferromagnetic, FM, and nonmagnetic, NM, multilayers with a large room-temperature magnetoresistance, MR, and strong magnetic anisotropy, MA, under a small externally applied magnetic field, H, remains a subject of scientific and technical interest. Recent advances in nanofabrication and characterization techniques have further opened up several new ways through which MR, sensitivity to H, and MA of the FM/NM multilayers could be dramatically improved in miniature devices such as smart spin-valves based biosensors, non-volatile magnetic random access memory, and spin transfer torque nano-oscillators. This review presents in detail the fabrication and characterization of a few representative FM/NM multilayered films—including the nature and origin of MR, mechanism associated with spin-dependent conductivity and artificial generation of MA. In particular, a special attention is given to the Pulsed-current deposition technique and on the potential industrial applications and future prospects. FM multilayers presented in this review are already used in real-life applications such as magnetic sensors in automobile and computer industries. These material are extremely important as they have the capability to efficiently replace presently used magnetic sensors in automobile, electronics, biophysics, and medicine, among many others.
Highlights
Ferromagnetic (FM) multilayered films are important materials because they exhibit interesting physical properties such as giant magnetoresistance (GMR) [1,2,3,4,5,6], magnetic anisotropy (MA) [7,8,9], tunneling magnetoresistance (TMR) [10], surface plasmon-resonance (SPR) and giant magneto-reflectivity (GMRE) [11,12,13,14]
The present review focuses on the latter three types of MR effects—including spin torque transfer (STT) effect and, in particular, why these effects are important in FM multilayers and on how the mechanism responsible for MR effects can be significantly different in FM-based multilayered films as opposed to MR effects exhibited by conventional metals and FM alloys
An electrical resistance is called giant magnetoresistance (GMR) when a small externally applied magnetic field, H, can cause a large change in ρ; usually larger by several orders of magnitude compared to the anisotropic magnetoresistance (AMR) effect that is normally observed in FM metals and their alloys
Summary
Ferromagnetic (FM) multilayered films are important materials because they exhibit interesting physical properties such as giant magnetoresistance (GMR) [1,2,3,4,5,6], magnetic anisotropy (MA) [7,8,9], tunneling magnetoresistance (TMR) [10], surface plasmon-resonance (SPR) and giant magneto-reflectivity (GMRE) [11,12,13,14]. Our recent experimental observations have shown that obliquely deposited as well as externally -induced metals and multilayered films of FM exhibit strong in-plane or perpendicular-to-plane uniaxial MA, depending on FM layer thickness [7,40]. Magnetic properties such as the coercivity, Hc and remanence, Mr, are strongly affected by anisotropy energy of a magnetic multilayer. The magnitude of MR can be positive (increasing) or negative (decreasing) and this largely depends on the following factors: electronic configuration of metals used, on their shape, size and thickness, layer composition, and on the direction of the externally applied H field or current, I [43]. The present review focuses on the latter three types of MR effects—including spin torque transfer (STT) effect and, in particular, why these effects are important in FM multilayers and on how the mechanism responsible for MR effects can be significantly different in FM-based multilayered films as opposed to MR effects exhibited by conventional metals and FM alloys
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