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Magnetic Particle Biosensors
Published in Jeffrey N. Anker, O. Thompson Mefford, Biomedical Applications of Magnetic Particles, 2020
Yunzi Li, Paivo Kinnunen, Alexander Hrin, Mark A. Burns, Raoul Kopelman
Spin valves are another method of single-particle detection that has been widely investigated (Ferreira et al. 2003, Heim et al. 1994, Li et al. 2003, 2006, Loureiro et al. 2009, Jeong Dae, Sang Don, and Myung Ae 2009, Lagae et al. 2002). Spin valves rely on an anisotropic magnetic resistance (AMR) in order to detect very small magnetic fields. The essence of spin-valve technology is a coupling of ferromagnetic thin films across a non-magnetic metal layer (Dieny et al. 1991, Ferreira et al. 2003, Speriosu et al. 1991). In spin valves, the resistance of the material changes depends on the angle between the magnetization directions of the two ferromagnetic layers. Most spin valves today also use an additional ferrimagnetic layer to “pin” the orientation of the magnetic moment of one of the ferromagnetic layers. Figure 9.9 shows the basic setup of the sensor. The single magnetic particle can then be detected by the way it affects the orientation of the magnetic moment of the other ferromagnetic layer. Of all the single-particle detection mechanisms, spin valves are among the most researched and furthest along in detection of biological agents. Spin valves have been both employed in microarrays of sensors (Wang et al. 2005), detection of DNA oligonucleotides (Graham et al. 2005, Ferreira et al. 2005), and cell counting (Loureiro et al. 2009, 2011).
Spin Torque in Magnetic Systems
Published in Evgeny Y. Tsymbal, Žutić Igor, Spintronics Handbook: Spin Transport and Magnetism, Second Edition, 2019
Aurélien Manchon, Shufeng Zhang
Careful inspection of the equation of motion of the order parameter suggests that the torque enabling current-driven switching must be even upon magnetization reversal [130], i.e. on the form ~n×(p×n), where n is the order parameter direction and p is an arbitrary vector determined by the source of the spin torque. Several theoretical studies have been conducted to uncover the nature of spin torque in spin valves involving antiferromagnets [131, 132]. An important feature of spin valves is that the spin density acquired in one side of the device needs to be coherently transmitted toward the other part of the device without alteration. This works well in ferromagnetic spin valves but dramatically fails in their antiferromagnetic counterparts: due to the staggered nature of the magnetic configuration in antiferromagnets, the spin torque is very sensitive to disorder [133, 134], which makes its experimental observation a very challenging task [21].
Synthesis and Applications of 2d Transition Metal Dichalcogenides
Published in Jiabao Yi, Sean Li, Functional Materials and Electronics, 2018
The most successful application of spintronics is in the field of data storage followed discovery of giant magnetoresistance (GMR) via spin- dependent electron transport in metallic multilayers [119]. GMR is first observed in thin-film structures composed of alternating ferromagnetic and nonmagnetic conductive layers. The resistance of the material is determined by the alignment of spins in the ferromagnetic layers. A spin valve is a GMR- based device with a sandwich structure in which two ferromagnetic layers are separated by a nonmagnetic layer [120]. One of the ferromagnetic layers is pinned and the other one is free, in other words, only the magnetization of the free layer can be flipped by an applied magnetic field. As the orientations of magnetizations in two layers change from parallel to antiparallel, the resistance of the spin valve gives a slight rise from 5% to 10%. MoS2-based spin valve can be constructed by using two Permalloy (Py, Ni80Fe20) electrodes as the ferromagnetic layers [121]. The MoS2 films showed metallic behavior rather than semiconducting, due to the strong hybridization with Fe and Ni atoms in the electrodes. The highest magnetoresistance of the spin valve was ~0.73% at 10 K, which is far from satisfaction for practical applications. However, additional first principle calculation indicates that an ideal magnetoresistance of ~9% can be achieved for a perfect Py/MoS2/Py junction, suggesting promising candidate for spintronics applications.
Structural properties of Fe–Ni/Cu/Fe–Ni trilayers on Si(100)
Published in Phase Transitions, 2021
Ananya Sahoo, Maheswari Mohanta, S. K. Parida, V. R. R. Medicherla
Ferromagnetic (FM) multilayers are considered as important materials by physicists and engineers in the recent past due to the novel and exciting physical properties such as giant magnetoresistance (GMR) [1–4], tunneling magnetoresistance (TMR) [5], magnetic anisotropy [6], surface plasmon resonance and giant magneto-reflectivity (GMRE) [7, 8] they exhibit. The fundamental physics of the novel magnetoresistive phenomena in magnetic multilayers is still elusive [9, 10]. The magnetic multilayers can be used in panoply of technological applications. The best application of them is in the fabrication of devices that utilize the spin of the electron [11]. One such device called the spin valve can be used as read head for computer hard disks. The spin valves can also be used in non-volatile random access memory structures. The emergence of magnetoelectronics can bring a sea change in the electronics industry. The magnetic multilayers play a key role in improving the data storage density. A recent review by Rizal et al. [12] describes in detail the fabrication and characterization of the magnetic multilayers consisting of alternate stacks of FM and nonmagnetic (NM) layers. The observed GMR in magnetic multilayers was attributed to spin- dependent scattering at the interface [1, 9]. The spin-dependent scattering at the bulk of the FM layer was also included to obtain GMR along with interfacial scattering [13, 14].
Spin-resolved transport properties of atomic carbon chain between sawtooth zigzag-edge graphene nanoribbons electrodes
Published in Molecular Physics, 2021
Haiqing Wan, Xianbo Xiao, Guanghui Zhou, Wei Hu
In summary, we have proposed Spintronics and magnetic molecular device, which is constructed by a carbon chain (C) sandwiched between two STGNRs (5, 3) electrodes. It is found by the theoretical investigation that the unusual dual spin-filtering effect with the spin filtering efficiency up to 100, high-performance dual-spin diode effect with the rectification ratio up to about and obvious NDR behaviour with the peak-to-valley ratio up to about can be achieved. Particularly, a giant magnetoresistance ratio approach which displays the potential of usage as a highly effective spin-valve device. The analysis of transmission coefficients and the evolution of electrode band structures indicate that the perfect dual-spin filter and spin diode effect are due to a dual selection rule, i.e.simultaneous presence of open conductance channels on the chain atoms and in the contact region making the electronic band-to-band tunnelling available. However, the NDR behaviours originate from the conduction orbital being suppressed by the bias-induced molecular orbital movement and decreasing overlap for both spin band between two STGNR(5, 3) electrodes. These findings suggest that our proposed model device C-STGNRs have a promising performance for perfect spin-filter, spin-diode, spin-switching, and so on.
Exchange bias effect revealed by irreversible structural transformation between the HCP and FCC structures of Cobalt nanoparticles
Published in Phase Transitions, 2020
Exchange bias was first observed in Co/CoO particles by Meiklejohn and Bean in 1956 [1–3]. With this discovery, it became important to understand the fundamental role of the bias effect following the emergence of other effects like Giant magnetoresistance and Tunneling magnetoresistance. In addition, many new studies have been carried out to understand the processes governing the bias effect and to obtain a new generation of bias-effective materials. This new generation of materials enables the emergence of new technological products with high commercial value, such as spin valves, high capacity magnetic recording and reading-writing devices. The number of these studies is continuously increasing. For example, the bias effect has been investigated experimentally in numerous materials, including Ni–Mn [4–6], Cu–Mn [7], Ag–Mn [8], Co–Mn [9] and Fe–Mn [10] binary alloys, Ni2MnGa [11], Cu44.7Mn20.6Al37.7 [12], Ni50Mn25+xSb25−x [13], Ni50Mn36Sn14 [14] and Ni49.5Mn34.5In16 [15] ternary alloys, Pr1/3Ca2/3MnO3 [16], CaMnO3 [17], La0.25Ca0.75MnO3 [18], La0.2Ca0.8MnO3 [19], Pr0.5Ca0.5MnO3 [20], Nd0.5Ca0.5MnO3 [21], Sm0.5Ca0.5MnO3 [22], La1−xSrxMnO3 [23] and Sr2FeMoO6 [24] perovskite minerals, BiFeO3 [25,26] and BaTiO3 [27] Ferrite films, Fe/Fe [28,29], Co/CoO [30] and Ni/NiO [31–33] core/shell nanostructures, MnN [34], D019 Mn2FeGa [35] and Mn3Ga [36].