Electrons have a charge and a spin, but until recently these were considered separately. In classical electronics, charges are moved by electric fields to transmit information and are stored in a capacitor to save it. In magnetic recording, magnetic fields have been used to read or write the information stored on the magnetization, which 'measures' the local orientation of spins in ferromagnets. The picture started to change in 1988, when the discovery of giant magnetoresistance opened the way to efficient control of charge transport through magnetization. The recent expansion of hard-disk recording owes much to this development. We are starting to see a new paradigm where magnetization dynamics and charge currents act on each other in nanostructured artificial materials. Ultimately, 'spin currents' could even replace charge currents for the transfer and treatment of information, allowing faster, low-energy operations: spin electronics is on its way.

/pdf/the-emergence-of-spin-electronics-in-data-storage-1vrnm5549k.pdf

The emergence of spin electronics in data storage

“Spintronics,” in which both the spin and charge of electrons are used for logic and memory operations, promises an alternate route to traditional semiconductor electronics. A complete logic architecture can be constructed, which uses planar magnetic wires that are less than a micrometer in width. Logical NOT, logical AND, signal fan-out, and signal cross-over elements each have a simple geometric design, and they can be integrated together into one circuit. An additional element for data input allows information to be written to domain-wall logic circuits.

http://science.sciencemag.org/content/sci/309/5741/1688.full.pdf

Magnetic Domain-Wall Logic

Antiferromagnetic materials are magnetic inside, however, the direction of their ordered microscopic moments alternates between individual atomic sites. The resulting zero net magnetic moment makes magnetism in antiferromagnets invisible on the outside. It also implies that if information was stored in antiferromagnetic moments it would be insensitive to disturbing external magnetic fields, and the antiferromagnetic element would not affect magnetically its neighbors no matter how densely the elements were arranged in a device. The intrinsic high frequencies of antiferromagnetic dynamics represent another property that makes antiferromagnets distinct from ferromagnets. The outstanding question is how to efficiently manipulate and detect the magnetic state of an antiferromagnet. In this article we give an overview of recent works addressing this question. We also review studies looking at merits of antiferromagnetic spintronics from a more general perspective of spin-ransport, magnetization dynamics, and materials research, and give a brief outlook of future research and applications of antiferromagnetic spintronics.

Antiferromagnetic spintronics

http://files.janapv.webnode.cz/200000097-8a03f8afdf/ex_bias_nano.pdf

Exchange bias in nanostructures

Electrons have a charge and a spin, but until recently, charges and spins have been considered separately. In conventional electronics, the charges are manipulated by electric fields but the spins are ignored. Other classical technologies, magnetic recording, for example, are using the spin but only through its macroscopic manifestation, the magnetization of a ferromagnet. This picture started to change in 1988 when the discovery Baibich et al., 1988; Binash et al., 1989 of the giant magnetoresistance GMR of the magnetic multilayers opened the way to an efficient control of the motion of the electrons by acting on their spin through the orientation of a magnetization. This rapidly triggered the development of a new field of research and technology, today called spintronics and, like the GMR, exploiting the influence of the spin on the mobility of the electrons in ferromagnetic materials. Actually, the influence of the spin on the mobility of the electrons in ferromagnetic metals, first suggested by Mott 1936 , had been experimentally demonstrated and theoretically described in my Ph.D. thesis almost 20 years before the discovery of 1988. The GMR was the first step on the road of the exploitation of this influence to control an electrical current. Its application to the read heads of hard disks greatly contributed to the fast rise in the density of stored information and led to the extension of the hard disk technology to consumer’s electronics. Then, the development of spintronics revealed many other phenomena related to the control and manipulation of spin currents. Today this field of research is expanding considerably, with very promising new axes like the phenomena of spin transfer, spintronics with semiconductors, molecular spintronics, or single-electron spintronics.

/pdf/nobel-lecture-origin-development-and-future-of-spintronics-3cohq1g5co.pdf

Nobel Lecture: Origin, development, and future of spintronics

A 4-Mb magnetoresistive random access memory (MRAM) with a novel magnetic bit cell and toggle switching mode is presented. The circuit was designed in a five level metal, 0.18-mum complementary metal-oxide-semiconductor process with a bit cell size of 1.55 mum2. The new bit cell uses a balanced synthetic antiferromagnetic free layer and a phased write pulse sequence to provide robust switching performance with immunity from half-select disturbs. This switching mode greatly improves the operational performance of the MRAM as compared to conventional MRAM. A detailed description of this 4-Mb toggle MRAM is presented

A 4-Mb toggle MRAM based on a novel bit and switching method

Spin-transfer in nanometre-scale magnetic devices results from the torque on a ferromagnet owing to its interaction with a spin-polarized current and the electrons' spin angular momentum. Experiments have detected either a reversal or high-frequency (GHz) steady-state precession of the magnetization in giant magnetoresistance spin valves and magnetic tunnel junctions with current densities of more than 10(7) A cm(-2). Spin-transfer devices may enable high-density, low-power magnetic random access memory or direct-current-driven nanometre-sized microwave oscillators. Here we show that the magnetization oscillations induced by spin-transfer in two 80-nm-diameter giant-magnetoresistance point contacts in close proximity to each other can phase-lock into a single resonance over a frequency range from approximately 24 GHz for contact spacings of less than about approximately 200 nm. The output power from these contact pairs with small spacing is approximately twice the total power from more widely spaced (approximately 400 nm and greater) contact pairs that undergo separate resonances, indicating that the closely spaced pairs are phase-locked with zero phase shift. Phase-locking may enable control of large arrays of coupled spin-transfer devices with increased power output for microwave oscillator applications.

Phase-locking in double-point-contact spin-transfer devices

The present invention provides microfluidic devices that can be used to effect a number of manipulations on a sample to ultimately result in target analyte detection or quantification. The device provides at least one magnetic microchannel that is capable of separating magnetic or magnetically-labeled target analytes from non-magnetic materials. Further, a magnetic microchannel may sort materials according to their magnetic response. Alternatively, magnetic or magnetically-labeled components other than the target analytes can be retained by the magnetic microchannel and are thus removed from the target analytes. Depending on the specificity of the binding ligand, one can either separate a vast population of analytes sharing a common binding motif, or specifically retain a rare target analyte because of its recognition of a specific ligand on the magnetic particle.

Microfluidic devices for high gradient magnetic separation

A magnetoresistive tunneling junction memory cell (10) comprising a pinned ferromagnetic region (17) having a magnetic moment vector (47) fixed in a preferred direction in the absence of an applied magnetic field wherein the pinned ferromagnetic region has a magnetic fringing field (96), an electrically insulating material positioned on the pinned ferromagnetic region to form a magnetoresistive tunneling junction (16), and a free ferromagnetic region (15) having a magnetic moment vector (53) oriented in a position parallel or anti-parallel to that of the pinned ferromagnetic region wherein the magnetic fringing field is chosen to obtain a desired switching field.

Magnetoresistive random access memory with reduced switching field

A method of fabricating a cladding region for use in MRAM devices includes the formation of a conductive bit line proximate to a magnetoresistive memory device. The conductive bit line is immersed in a first bath containing dissolved ions of a first conductive material for a time sufficient to displacement plate a first barrier layer on the conductive line. The first barrier layer is then immersed in an electroless plating bath to form a flux concentrating layer on the first barrier layer. The flux concentrating layer is immersed in a second bath containing dissolved ions of a second conductive material for a time sufficient to displacement plate a second barrier layer on the flux concentrating layer.

Bradley N. Engel

Papers

A 4-Mb toggle MRAM based on a novel bit and switching method

Phase-locking in double-point-contact spin-transfer devices

Microfluidic devices for high gradient magnetic separation

Magnetoresistive random access memory with reduced switching field

Method of applying cladding material on conductive lines of MRAM devices