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

An MRAM cell and a method of programming the cell are disclosed. The cell includes a free layer of magnetic material having a ferromagnetic resonance with a resonant frequency, the ferromagnetic resonance having a Q greater than one. A hard axis and an easy axis write line are positioned in magnetic communication with the free layer. A cladding layer partially surrounds the hard axis write line and has a similar resonant frequency and with a ferromagnetic resonance Q greater than one. A write signal including the resonant frequency is applied to the hard axis write line and simultaneously a write pulse is applied to the easy axis write line. The Qs of the cell and the cladding layer multiply to substantially increase the switching magnetic field or reduce the current required to provide the same magnetic field.

Mram write apparatus and method

A method of fabricating a magnetoresistive tunneling junction cell comprising the steps of providing a substrate with a surface, depositing a first magnetic region (17) having a resultant magnetic moment vector onto the substrate, depositing an electrically insulating material (16) onto the first magnetic region, and depositing a second magnetic region (15) onto the electrically insulating material, wherein at least a portion of one of the first and second magnetic regions is formed by depositing said region at a nonzero deposition angle relative to a direction perpendicular to the surface of the substrate to create an induced anisotropy.

Oblique deposition to induce magnetic anisotropy for MRAM cells

Magnetoresistive random-access memory (MRAM) is a new memory technology that is nearing commercialization. MRAM integrates a magnetic tunnel junction (MTJ) device with standard silicon-based microelectronics, resulting in a combination of qualities not found in other memory technologies. For example, MRAM is nonvolatile, has unlimited read and write endurance, and is capable of high-speed read and write operations. In this article, we will describe the fundamentals of an MTJ-based MRAM as well as recent important technology developments in the areas of magnetic materials and memory cell architecture. In addition, we will compare the present and future capabilities of MRAM to those of existing memory technologies such as static RAM and flash memory.

Nonvolatile Magnetoresistive Random-Access Memory Based on Magnetic Tunnel Junctions

A nearly balanced synthetic antiferromagnetic (SAF) structure that can be advantageously used in magnetoelectronic devices such as a magnetoresistive memory cell includes two ferromagnetic layers and an antiferromagnetic coupling layer separating the two ferromagnetic layers. The SAF free layer has weakly coupled regions formed in the antiferromagnetic coupling layer by a treatment such as annealing, layering of the antiferromagnetic coupling layer, or forming the antiferromagnetic coupling layer over a roughened surface of a ferromagnetic layer. The weakly coupled regions lower the flop field of the SAF free layer in comparison to untreated SAF free layers. The SAF flop is used during the write operation of such a structure and its reduction results in lower power consumption during write operations and correspondingly increased device performance.

Synthetic antiferromagnetic structure for magnetoelectronic devices

A magnetoelectronics information device (20) is provided that includes two multi-layer structures (24, 26) and a spacer layer (28) interposed between the two multi-layer structures. Each of the multi-layer structures has two magnetic sublayers (38, 40, and 44, 46) and a spacer layer (42, 48) interposed between the two magnetic sublayers. The spacer layer interposed between the two magnetic sublayers provides an antiferromagnetic exchange coupling that is quantified by a saturation field. The spacer layer interposed between the two multi-layer structures provides a second antiferromagnetic exchange coupling is quantified by another saturation field that is less than the first saturation field.

Bradley N. Engel

Papers

Mram write apparatus and method

Oblique deposition to induce magnetic anisotropy for MRAM cells

Nonvolatile Magnetoresistive Random-Access Memory Based on Magnetic Tunnel Junctions

Synthetic antiferromagnetic structure for magnetoelectronic devices

Magnetoelectronics information device having a compound magnetic free layer