Electrical control of magnetic properties is crucial for device applications in the field of spintronics. Although the magnetic coercivity or anisotropy has been successfully controlled electrically ...in metals as well as in semiconductors, the electrical control of Curie temperature has been realized only in semiconductors at low temperature. Here, we demonstrate the room-temperature electrical control of the ferromagnetic phase transition in cobalt, one of the most representative transition-metal ferromagnets. Solid-state field effect devices consisting of a ultrathin cobalt film covered by a dielectric layer and a gate electrode were fabricated. We prove that the Curie temperature of cobalt can be changed by up to 12 K by applying a gate electric field of about ±2 MV cm(-1). The two-dimensionality of the cobalt film may be relevant to our observations. The demonstrated electric field effect in the ferromagnetic metal at room temperature is a significant step towards realizing future low-power magnetic applications.
The spin transfer torque is essential for electrical magnetization switching. When a magnetic domain wall is driven by an electric current through an adiabatic spin torque, the theory predicts a ...threshold current even for a perfect wire without any extrinsic pinning. The experimental confirmation of this 'intrinsic pinning', however, has long been missing. Here, we give evidence that this intrinsic pinning determines the threshold, and thus that the adiabatic spin torque dominates the domain wall motion in a perpendicularly magnetized Co/Ni nanowire. The intrinsic nature manifests itself both in the field-independent threshold current and in the presence of its minimum on tuning the wire width. The demonstrated domain wall motion purely due to the adiabatic spin torque will serve to achieve robust operation and low energy consumption in spintronic devices.
Controlling the displacement of a magnetic domain wall is potentially useful for information processing in magnetic non-volatile memories and logic devices. A magnetic domain wall can be moved by ...applying an external magnetic field and/or electric current, and its velocity depends on their magnitudes. Here we show that the applying an electric field can change the velocity of a magnetic domain wall significantly. A field-effect device, consisting of a top-gate electrode, a dielectric insulator layer, and a wire-shaped ferromagnetic Co/Pt thin layer with perpendicular anisotropy, was used to observe it in a finite magnetic field. We found that the application of the electric fields in the range of ± 2-3 MV cm(-1) can change the magnetic domain wall velocity in its creep regime (10(6)-10(3) m s(-1)) by more than an order of magnitude. This significant change is due to electrical modulation of the energy barrier for the magnetic domain wall motion.
Controlling the position of a magnetic domain wall with electric current may allow for new types of non-volatile memory and logic devices. To be practical, however, the threshold current density ...necessary for domain wall motion must be reduced below present values. Intrinsic pinning due to magnetic anisotropy, as recently observed in perpendicularly magnetized Co/Ni nanowires, has been shown to give rise to an intrinsic current threshold J(th)(0). Here, we show that domain wall motion can be induced at current densities 40% below J(th)(0) when an external magnetic field of the order of the domain wall pinning field is applied. We observe that the velocity of the domain wall motion is the vector sum of current- and field-induced velocities, and that the domain wall can be driven against the direction of a magnetic field as large as 2,000 Oe, even at currents below J(th)(0). We show that this counterintuitive phenomenon is triggered by Walker breakdown, and that the additive velocities provide a unique way of simultaneously determining the spin polarization of current and the Gilbert damping constant.
MRAM Cell Technology for Over 500-MHz SoC Sakimura, N.; Sugibayashi, T.; Honda, T. ...
IEEE journal of solid-state circuits,
04/2007, Letnik:
42, Številka:
4
Journal Article, Conference Proceeding
Recenzirano
This paper describes newly developed magnetic random access memory (MRAM) cell technology suitable for high-speed memory macros embedded in next-generation system LSIs: a two-transistor one-magnetic ...tunneling junction (2T1MTJ) cell structure, a write-line-inserted MTJ, and a 5T2MTJ cell structure. The 2T1MTJ cell structure makes it possible to significantly improve the write margin and accelerate the operating speed to 200 MHz. Its high compatibility with SRAM specifications and its wide write margin were confirmed by measuring 2T1MTJ MRAM test chips. Although the cell structure requires a small-writing-current MTJ, the current can be reduced to 1mA using the newly developed write-line-inserted MTJ. Further development to reduce the current down to 0.5 mA is required to obtain a cell area of 1.9 mum 2 , which is smaller than the SRAM cell area, in the 0.13-mum CMOS process. The 5T2MTJ cell structure also enables random-access operation over 500 MHz because the sensing signal is amplified in each cell. Random access time of less than 2 ns can be achieved with SPICE simulation when the magnetic resistance is 5 kOmega and the magnetoresistive (MR) ratio is more than 70%
In this paper, we have calculated the intrinsic threshold current density of domain wall (DW) motion in nanostrips with perpendicular magnetic anisotropy (PMA) and have estimated writing properties ...of magnetic random access memories (MRAMs) with DW motion. Carrying out a micromagnetic simulation, we revealed that the intrinsic threshold current density decreases with decreases in the strip thickness, width, and magnetization, whereas it did not depend significantly on magnetocrystalline anisotropy and exchange stiffness. These results showed good agreement with one-dimensional (1-D) analysis. We also found that current-induced DW motion in PMA strips may have potential for use in low-write-current MRAMs. For a width of less than roughly 100 nm, comparable properties to those of existing memories can be obtained.
We have investigated the influence of a stray field on a magnetic domain wall (DW). The depinning fields of a DW in a perpendicularly magnetized Co/Ni nanowire with partly-stacked Ni
81
Fe
19
/SiO
2
...islands on it was measured. The depinning field for the wire with Ni
81
Fe
19
/SiO
2
was found to be higher than that for the wire without the stack, indicating that the stray field from the Ni
81
Fe
19
/SiO
2
stack clearly served as an artificial pinning site for the DW. The magnetic force microscopy observation evidenced that the DW was pinned near the Ni
81
Fe
19
stack.
To demonstrate the presence of a soluble isoform of P-selectin predicted from cDNA sequencing (Johnston, G.I., Bliss, G.A.,
Newman, P.J., and McEver, R.P. (1990) J. Biol. Chem. 265, 21381-21385), we ...immunoisolated and compared structurally P-selectin
from fresh frozen human plasma with that from washed intact platelets. Plasma P-selectin was reactive with rabbit antiserum
to a synthesized peptide (residues 762-774 of mature P-selectin) but was significantly less reactive with antibody to a peptide
(residues 747-760). In contrast, platelet P-selectin reacted with both antibodies. S-Pyridylethylated plasma P-selectin was
fractionated by reversed phase-high performance liquid chromatography into two major species. From platelets, two virtually
identical species were separated. Sequential digestion with Achromobacter protease I and then Staphylococcus V8 protease produced
peptides assigned to the tail region of the protein including the putative spliced site. From the more hydrophilic species
in both plasma and platelets, a peptide completely lacking the sequence of the putative spliced site was identified. In contrast,
the more hydrophobic species yielded a peptide with an intact transmembrane sequence. Hence, these results provide direct
evidence that the previously predicted soluble isoform of P-selectin is actually synthesized in vivo and is present as a circulating
molecule.
We have proposed detecting a domain wall behavior in a strip with perpendicular magnetic anisotropy by measuring both extraordinary Hall effect and domain wall resistance with unique placement of ...three via contacts. By using this detecting technique, we have confirmed that the domain wall can be initialized at the boundary of the stepped structure of a Co/Pt multilayer strip. We have observed nucleation independent of the current direction and the propagation depending on it. We could not find any domain wall motion by spin-transfer torque from the boundary until 1.8 times 10 12 A/m 2 , probably because of the smaller polarization and/or the larger damping constant of the Co/Pt multilayer.
A 16-Mb Toggle MRAM With Burst Modes Sugibayashi, T.; Sakimura, N.; Honda, T. ...
IEEE journal of solid-state circuits,
11/2007, Letnik:
42, Številka:
11
Journal Article
Recenzirano
This paper describes a recently developed 16-Mb toggle magnetic random access memory (MRAM). It has 100-MHz burst modes that are compatible with a pseudo-SRAM even though the toggle cell requires ...reading and comparing sequences in write modes. To accelerate operating clock frequency, we propose a distributed-driver wide-swing current-mirror scheme, an interleaved and pipelined memory-array group activation scheme, and a noise-insulation switch scheme. These circuit schemes compensate the toggle cell timing overhead in write modes and maintain write-current precision that is essential for the wide operational margin of MRAMs. Because toggle cells are very resistant to write disturbance errors, we designed the 16-Mb MRAM to include a toggle MRAM cell. The MRAM was fabricated with 0.13-mum CMOS and 0.24-mum MRAM processes with five metal layers.
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