Discovery Of Giant Magnetoresistance Research Articles

Intercalated chiral-molecular 2D superlattice for spintronics

Solid-state spintronic devices are energy-efficient for data storage and energy harvesting. This field is revolutionized by the discovery of giant magnetoresistance. Recently, Qian et al. fabricated an intercalated chiral-molecular two-dimensional superlattice that exhibits highly efficient chiral-induced spin selectivity. They demonstrated a tunneling magnetoresistance ratio of >300% and a spin polarization ratio of >60%, which opens up promising future applications in spintronic devices.

Current Progress of Magnetoresistance Sensors

Magnetoresistance (MR) is the variation of a material’s resistivity under the presence of external magnetic fields. Reading heads in hard disk drives (HDDs) are the most common applications of MR sensors. Since the discovery of giant magnetoresistance (GMR) in the 1980s and the application of GMR reading heads in the 1990s, the MR sensors lead to the rapid developments of the HDDs’ storage capacity. Nowadays, MR sensors are employed in magnetic storage, position sensing, current sensing, non-destructive monitoring, and biomedical sensing systems. MR sensors are used to transfer the variation of the target magnetic fields to other signals such as resistance change. This review illustrates the progress of developing nanoconstructed MR materials/structures. Meanwhile, it offers an overview of current trends regarding the applications of MR sensors. In addition, the challenges in designing/developing MR sensors with enhanced performance and cost-efficiency are discussed in this review.

Spintronics for Energy- Efficient Computing: An Overview and Outlook

From the discovery of giant magnetoresistance (GMR) to tunnel magnetoresistance (TMR), their subsequent application in large capacity hard disk drives (HDDs) greatly speeded up the information era over the past decades. However, the growing demand for big-data storage and processing is limited by the von-Neumann architecture due to the memory bottleneck and power dissipation. Taking advantage of nonvolatility, high speed, and low power, magnetic random access memory (MRAM) becomes a promising candidate to overcome this limitation through processing-in-memory (PIM) architectures. In this article, we provide an overview of existing technology and give a roadmap of spintronic devices for future energy-efficient computing and its relevant integration architectures. We begin with the fundamentals of Toggle-MRAM and spin-transfer torque (STT)-MRAM, which already have commercial applications. We then introduce spin-orbit torque (SOT), a critical mechanism to realize low-power data manipulation in the next generation of MRAM and summarize the recent experimental breakthroughs of field-free SOT switching schemes. Finally, we present MRAM-based PIM architectures and novel spintronic devices, provide an application outlook, and deliver the future development potential of energy-efficient computing systems.

Spin current as a probe of quantum materials.

Spin current historically referred to the flow of electrons carrying spin information, in particular since the discovery of giant magnetoresistance in the 1980s. Recently, it has been found that spin current can also be mediated by spin-triplet supercurrent, superconducting quasiparticles, spinons, magnons, spin superfluidity and so on. Here, we review key progress concerning the developing research direction utilizing spin current as a probe of quantum materials. We focus on spin-triplet superconductivity and spin dynamics in the ferromagnet/superconductor heterostructures, quantum spin liquids, magnetic phase transitions, magnon-polarons, magnon-polaritons, magnon Bose-Einstein condensates and spin superfluidity. The unique characteristics of spin current as a probe will be fruitful for future investigation of spin-dependent properties and the identification of new quantum materials.

The influence on hysteresis from the ending pinning design of GMR free layer

With the discovery of Giant Magneto Resistance (GMR), the spin valve GMR sensor based on the effect gets developed rapidly in all areas. However, there is always error in measuring result of spin valve GMR sensor because of hysteresis, which will limit widespread use of the sensor. Started with sensor structure, the paper puts coercivity as an important index to evaluate hysteresis characteristics. And a new method is proposed to reduce the hysteresis, namely with anti-ferromagnetic materials to pin the end of free layer. On this basis, the influence of pinning shape and pinning angle on hysteresis is focused research by theory and simulation at the same time. The results show that with the constant pinned area, the hysteresis is irrelevant with pinning shape, and different pinning angle will induce the change of hysteresis characteristic. The investigation will establish a theoretical basis for designing a low coercivity spin valve GMR sensor.

GMR Materials: A New Generation of Miniaturizated Technology

The discovery of GMR opened new windows in the field of nano-materials, and nowadays research in these materials has become fashionable due to its tremendous technological potential and the deep fundamental physics involved in it. The discovery of giant magneto-resistance (GMR) has been a huge impact on our life, especially for mass data storage devices. Initial experiments conducted by Grunberg and Fert are explained. Basic physics of the GMR effect can be explained by the two-current model, which the conduction of a current is, consist of two different spin electrons. Details of GMR applications, such as hard-disk read-heads, sensors and magnetic memory chips are presented. One of the important aspects of GMR discovery was that it was immediately turned into commercially available products (the first GMR Hard disk head was introduced by IBM in 1997) with a giant market share. The highest storage capacity in the modern computers is attributed to the discovery of GMR. The story of GMR effect tells us how an unexpected scientific discovery could give rise to completely new technologies, new science and new commercial products, that means the new technology promises smaller and faster tools.

Giant magnetoresistance: history, development and beyond

With the discovery of giant magnetoresistance (GMR), research effort has been made to exploiting the influence of spins on the mobility of electrons in ferromagnetic materials and/or artificial structures, which has lead to the idea of spintronics. A brief introduction is given to GMR effects from scientific background to experimental observations and theoretical models. In addition, the mechanisms of various magnetoresistance beyond the GMR are reviewed, for instance, tunnelling magnetoresistance, colossal magnetoresistance, and magnetoresistance in ferromagnetic semiconductors, nanowires, organic spintronics and non-magnetic systems.

Focus on Spintronics and Spin Physics

AbstractIt is our pleasure to bring out this Focus Issue on Spintronics and Spin Physics. Spin is an important aspect of physics, ever since the concepts of intrinsic angular momentum by Samuel Goudsmit and George Uhlenbeck, and spin by Wolfgang Pauli were introduced nearly a century ago to explain the experimental observations. In the field of magnetism the electron spin plays the all‐important central role. While the study of magnetism has a long history, the function of electron spin in electron transport gained interest and importance only in the recent few decades. This is despite the fact that Mott used two spin‐current channels to explain the resistivity behavior in magnetic metals as far back as in the 1930s. Since the eighties, several terms such as magnetotransport and magnetoelectronics, have been used. However, the term spintronics has gained a considerable popularity recently. Professor Albert Fert and Professor Peter Grünberg received their Nobel Prize in 2007 for their discovery of Giant Magnetoresistance (GMR). Read sensors based on the concept of GMR in the late nineties and tunnel magnetoresistance (TMR) since the past several years, are utilized in hard‐disk drive products.The field of spintronics from the early stages of GMR further flourished with the discovery of TMR as well as spin‐torque transfer (STT) effect to switch magnetization or to move domain walls. These led to research in the areas of spin injection and manipulation in semiconductors, magnetic random access memory, magnetic logic devices, domain wall memory, and so on. As a result there are plenty of researchers all over the world pushing the frontiers in applied as well as fundamental aspects of the field.In this Focus Issue we present one Review@RRL on magnetic random access memory (MRAM). This review‐type article provides a perspective on materials with a perpendicular magnetic anisotropy. Pentalemma – a challenging situation to meet five different requirements of the MRAM is described in the paper. A review of current materials, potential candidates, and the challenges are presented.The contributed Letters cover various fields, ranging from fundamentals to device applications; papers on oxide materials discuss topics such as spin‐calorics, defect engineering of ferromagnetism in carbon doped ZnO, zinc ferrites with tunable electrical conductivity, and electronic structure of EuO spin filter tunnel contacts. On the topic of metallic films, the Letters cover FePt films for spintronics applications, Co‐doped FeSi films, and magnetic tunnel junctions with composite free layers. There are several other papers covering interactions between domain walls and magnetic vortex excitation. On the device front, the papers discuss spin‐torque oscillators and domain wall memories.We hope the Focus Issue will bring valuable knowledge for your research and stimulate more activity in the field of spintronics. We plan to have several special issues on spintronics in the future, as exciting results are appearing recurrently opening new areas of research (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Ultrafast magnetization dynamics of spintronic nanostructures

The ultrafast (sub-nanosecond) magnetization dynamics of ferromagnetic thin films and elements that find application in spintronic devices is reviewed. The major advances in the understanding of magnetization dynamics in the two decades since the discovery of giant magnetoresistance and the prediction of spin-transfer torque are discussed, along with the plethora of new experimental techniques developed to make measurements on shorter length and time scales. Particular consideration is given to time-resolved measurements of the magneto-optical Kerr effect, and it is shown how a succession of studies performed with this technique has led to an improved understanding of the dynamics of nanoscale magnets. The dynamics can be surprisingly rich and complicated, with the latest studies of individual nanoscale elements showing that the dependence of the resonant mode spectrum upon the physical structure is still not well understood. Finally, the article surveys the prospects for development of high-frequency spintronic devices and highlights areas in which further study of fundamental properties will be required within the coming decade.

Spin-transfer effect and its use in spintronic components

Spin-electronics is a very rapidly expanding area of R&D which merges magnetism and electronics (Nobel Prize 2007). Since the discovery of giant magnetoresistance in 1988, several breakthroughs have further boosted this field (spin-valves 1990, tunnel magnetoresistance 1995, spin transfer 1996, voltage controlled magnetic properties 2004). The phenomenon of spin-transfer is particularly attractive both from fundamental and applied view points. It provides a new way to manipulate the magnetisation of magnetic nanostructures by a spin-polarised current. Spinelectronics has found applications in hard disk drives (1998) and more recently in non-volatile standalone memories (MRAM = Magnetic Random Access Memory). The spin-transfer phenomenon provides a new write scheme in MRAM yielding a much better scalability of these devices towards the 22 nm node. Furthermore, besides MRAMs, hybrid CMOS/magnetic technology can yield a totally new approach in the way electronic devices are designed. Most CMOS devices such as microprocessors are based on Von Neumann architecture in which logic and memories are separate components. The unique set of characteristics combined within magnetic tunnel junctions: cyclability, switching speed, scalability, makes it possible to conceive novel electronic systems in which logic and memory are intimately combined in non-volatile logic components (concept of non-volatile CPU). The spin-transfer phenomenon can also be used to generate large amplitude steady magnetic excitations in magnetic nanostructures. This phenomenon can also be used to conceive new frequency tunable radiofrequency oscillators. The latter are very attractive for wireless applications which require scanning large frequency bandwidth.

Origin, Development, and Future of Spintronics (Nobel Lecture)

Going for a spin: The discovery of giant magnetoresistance (GMR) opened up a new area of technology—spintronics—which, in contrast to conventional electronics, uses not only the charge, but also the spin of the electron. Applications of GMR have revolutionized hard-disk technology (see picture). Albert Fert, Nobel laureate in Physics 2007, describes firsthand the discovery of GMR and the development of spintronics.

Nobel Focus: Sensitive Magnetic Sandwich

The 2007 Nobel Prize in Physics recognizes the discovery of giant magnetoresistance, which allowed dramatic improvements in memory density for disk drives (revised 23 October).

Negative spin polarization of theFe3O4∕γ−Al2O3interface measured by spin-resolved photoemission

We report on spin-resolved photoemission spectroscopy measurements at the interface between a $25\text{\ensuremath{-}}\mathrm{nm}$-thick ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}\phantom{\rule{0.3em}{0ex}}(111)$ thin film and a $2\text{\ensuremath{-}}\mathrm{nm}$-thick $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}\phantom{\rule{0.3em}{0ex}}(111)$ layer. The ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ layer remains stoichiometric even after being covered by $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ and exhibits a negative spin polarization of $\ensuremath{\sim}\ensuremath{-}40%$, after remanence correction. This value should be considered as a lower bound for the spin polarization and demonstrates that ${\mathrm{Fe}}_{3}{\mathrm{O}}_{4}$ remains a spin polarized material even after incorporation in a bilayer.

Spin dependent transport: GMR & TMR

The discovery of giant magnetoresistance in 1988 opened the large research field of ‘spintronics’. Twenty years later, a large number of devices makes use of the electron's spin, in addition to its charge, to control electronic transport properties. The physical origin of spintronic phenomena is the different conduction properties of the majority and minority spin electrons in a ferromagnetic metal. At an interface involving a ferromagnetic conductor, this leads to spin dependent conduction or tunneling properties. Here we present an overview of magnetotransport phenomena in structures involving metallic layers. To cite this article: A. Schuhl, D. Lacour, C. R. Physique 6 (2005).

Effect of magnetic flux distribution on GMR in Ag/Co multilayers

Since the discovery of giant magnetoresistance (GMR) in multilayers (MLs) various applications of this effect are studied. One practical feature of ML GMR sensing elements is the magnetic flux distribution in the direction perpendicular to the surface of ML in the current-in-plane geometry. It results from the fact that top and bottom ferromagnetic layers concentrate more magnetic flux than central layers of the stack. This effect is studied in this work in evaporated Ag/Co MLs deposited onto Si substrates. The thickness of Co was 1.2–1.4 nm, i.e. Co layers were continuous. Ag layers were 5.4–5.8 nm thick. Number of Ag/Co periods was only ≤5 to expose the relative influence of top and bottom parts of ML. To make the ML structure symmetrical, an additional Co layer was deposited as first on the substrate. Ag/Co MLs were analyzed by X-ray diffraction (XRD) and X-ray reflectivity (XRR). The magnetic flux distribution was simulated. GMR measurements were performed in dynamic conditions in the external ac field (50 Hz) with increasing swing. By simulations of XRR spectra the effective roughness of ML interfaces 0.4–0.8 nm was obtained. The GMR signal at RT increased with number of periods and the external field ≤16 kA/m up to approximately 2%. The influence of distribution of the magnetic flux density on GMR was inferred from the behavior of the positions of maxima of GMR on the magnetic field axis vs. number of periods. It can be explained by the statistical distribution of coercivity of different domains in Co layers.

Giant Magnetoresistance Phenomenon in Manganates

AbstractThe discovery of giant magnetoresistance (GMR) in rare earth manganates of the general formula Ln1–xAxMnO3 (Lnrare earth, A=divalent cation) has aroused much interest not only because of its technological implications, but also due to the fascinating features and mechanism of the phenomemon in these oxides. GMR is observed in these manganates when they become ferromagnetic and transform from an insulating state to a metallic state close to the Curie temperature. The essential features of magnetoresistance in the manganates can be understood on the basis of the double‐exchange mechanism, but this is too simplistic to account for all the observed data. The most curious property of the manganates relates to the high resistivity exhibited in the so‐called metallic state. Charge ordering competes with the double‐exchange interaction responsible for ferromagnetism and GMR in these materials. The charge‐ordered (charge‐crystal) insulating state in the rare earth manganates can be melted into a metallic and ferromagnetic charge‐liquid state by applying a magnetic field, thus providing a unique case of charge and spin separation in solids. The observation of GMR in Tl2Mn2O7 shows that there can be causes other than double‐exchange for the phenomenon.

Giant oxygen isotope shift in the magnetoresistive perovskite La1–xCaxMnO3+y

FERROMAGNETIC perovskites of the form La1–XMexMnO3–Y (where Me is Ca or Sr) have been known1 since 1950, but there has been a recent resurgence of interest following the discovery of giant magnetoresistance in this class of compounds2,3. The compounds contain both Mn3+ and Mn4+ ions; as the electronic ground state of the Mn3+ ions is degenerate, their energy is lowered by a spontaneous distortion of the surrounding lattice—the Jahn–Teller effect4. The charge carriers in these materials are strongly coupled to (and mediate the ferromagnetic interaction between) the manganese ions5, suggesting that localized lattice distortions could also play an important role in determining the electronic and magnetic properties of these compounds. Here we investigate this possibility by examining the effect on the ferromagnetic transition temperature of varying the oxygen isotope mass (replacing 16O with 18O). For La0.8Ca0.2MnO3+y, we measure an isotope shift of >20 K, significantly larger than that found for any magnetic or electronic phase transition in other oxides. In contrast, we observe no significant isotope shift for the structurally related ferromagnet SrRuO3, in which the Jahn–Teller effect is negligible. These results imply that the large isotope shift arises from coupling of the charge carriers to Jahn–Teller lattice distortions, and we suggest that such Jahn–Teller 'polarons' may also be responsible for the magnetoresistive properties of these materials.

Giant magnetoresistance in Ti2Mn2O7 with the pyrochlore structure

MATERIALS exhibiting giant magnetoresistance (GMR) undergo a large change in electrical resistance in response to an applied magnetic field. This effect is of technological interest as it can be exploited for the sensitive detection of magnetic fields in magnetic memory devices. A range of compounds have now been found to exhibit intrinsic GMR—these are all perovskites based on manganese oxide1–4. Here we report the observation of GMR in Ti2Mn2O7, which has a pyrochlore structure and thus differs both structurally and electronically from perovskites. At 135 K the magnetoresistance ratio (the change in resistance) reaches–86% at 7 tesla, comparable to the GMR response of perovskite materials. In contrast to the hole-doped perovskites, the charge carriers in our material are electrons, as determined from measurements of the Hall coefficient. The discovery of GMR in a second class of material expands the options for optimizing magnetoresistive properties for specific technological applications.

Materials science aspects in designing giant magnetoresistance in heterogeneous Cu1-xCox thin films

The recent discovery of giant magnetoresistance (GMR) in heterogeneous Cu1-xCox thin films has brought new insights in the phenomenon of GMR, which was previously believed to be restricted to multilayered structures only. Subsequent theoretical analyses of GMR in this new materials class have shown that GMR is mainly controlled by the mean radius and the volume fraction of single domain ferromagnetic particles. In addition to these parameters, the mean free path for electron in the non-magnetic matrix as well as coherency between particles and matrix are influencing the amplitude of GMR. Clearly, the key to increase the amplitude of GMR is to determine the decomposition kinetics and from which to optimize the single domain ferromagnetic Co particle size distribution in heterogeneous Cu1-xCox thin films.Cu81Col9 films, 50 nm in thickness, have been deposited by dc magnetron sputtering from separate Cu and Co targets onto 30 nm thick silicon nitride electron transparent grids.