By Topic

Magnetics, IEEE Transactions on

Issue 10 • Date Oct. 2009

Filter Results

Displaying Results 1 - 25 of 389
  • [Front cover]

    Publication Year: 2009 , Page(s): C1
    Save to Project icon | Request Permissions | PDF file iconPDF (250 KB)  
    Freely Available from IEEE
  • IEEE Transactions on Magnetics publication information

    Publication Year: 2009 , Page(s): C2
    Save to Project icon | Request Permissions | PDF file iconPDF (39 KB)  
    Freely Available from IEEE
  • Table of contents

    Publication Year: 2009 , Page(s): 3369 - 3396
    Save to Project icon | Request Permissions | PDF file iconPDF (180 KB)  
    Freely Available from IEEE
  • Intermag 2009 Conference Chair's Foreword

    Publication Year: 2009 , Page(s): 3397
    Save to Project icon | Request Permissions | PDF file iconPDF (78 KB) |  | HTML iconHTML  
    Freely Available from IEEE
  • Intermag 2009 Publication Committee

    Publication Year: 2009 , Page(s): 3398 - 3399
    Save to Project icon | Request Permissions | PDF file iconPDF (1495 KB)  
    Freely Available from IEEE
  • Beyond MRAM, CMOS/MTJ Integration for Logic Components

    Publication Year: 2009 , Page(s): 3400 - 3405
    Cited by:  Papers (6)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (733 KB) |  | HTML iconHTML  

    Spintronics is a new discipline in which the spin of the electron is used as an additional degree of freedom besides its electrical charge to build innovative electronic components. Magnetic materials can be used as spin polarizer/analyzer in association with semiconductors or insulators, resulting in hybrid CMOS/magnetic architectures. Magnetic Tunnel Junctions (MTJ) are the basic elements of a new kind of memory, called MRAM (Magnetic Random Access Memory). Besides MRAM, it has recently been shown that by combining MTJ and CMOS components, one can also develop new functionalities for logic devices. This paper aims at giving a general overview of these novel hybrid magnetic/CMOS architectures and the design tools required for their design. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • After Hard Drives—What Comes Next?

    Publication Year: 2009 , Page(s): 3406 - 3413
    Cited by:  Papers (69)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (725 KB) |  | HTML iconHTML  

    There are numerous emerging nonvolatile memory technologies, which have been proposed as being capable of replacing hard disk drives (HDDs). In this paper, the prospects for these alternative technologies to displace HDDs in 2020 are analyzed. In order to compare technologies, projections were made of storage density and performance in year 2020 for both hard disks and the alternative technologies, assuming the alternative technologies could solve their remaining problems and assuming that hard drives would continue to advance areal density at a pace of about 40% per year, which would result in a two-disk 2.5-in disk drive that stores approximately 40 Terabytes and costs about $40. A major conclusion of the study is that to compete with hard drives on a cost per terabyte basis will be challenging for any solid state technology, because the ITRS lithography roadmap limits the density that most alternative technologies can achieve. Those technologies with the best opportunity have a small cell size and the capability of storing multiple bits per cell. Phase change random access memory (PCRAM) and spin transfer torque random access memory (STTRAM) appear to meet these criteria. PCRAMs are being marketed by at least one supplier and therefore appear to be closer to practical realization. On the other hand, STTRAMs would appear to have a performance edge assuming they, too, can be brought to market with multiple bits per cell. Although there are technologies that are not limited by the lithography roadmap and thus have greater areal density potential, they tend to be further from practical realization. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Possible Spin Pumping Effects on Spin Torque Induced Magnetization Switching in Magnetic Tunneling Junctions

    Publication Year: 2009 , Page(s): 3414 - 3417
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (108 KB) |  | HTML iconHTML  

    Dependence of spin torque induced magnetization switching upon interfacial insulating layers properties of magnetic tunneling junctions (MTJ) are studied. For the same magnetic properties and patterning geometric dimensions, changes in MTJ interfacial insulating layers properties reveal interesting magnetization switching behaviors. These behaviors cannot be explained by conventional Landau-Lifshitz-Gilbert equation with a spin torque term and an intrinsic ferromagnetic relaxation damping. However the magnetization switching dynamics can be understood through assumption of spin pumping effects in magnetic tunneling junctions. This is not only important for fundamental understanding of spin and electronic transport in MTJ but also important for practical trade-offs between critical switching current and MTJ resistance for spin torque random access memory. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • High Level Oscillations With Narrow Linewidth in Magnetic Nano-Contact Spin Torque Oscillator With Synthetic AF Spin-Valve Structure

    Publication Year: 2009 , Page(s): 3418 - 3421
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (305 KB) |  | HTML iconHTML  

    We investigated the current induced magnetization dynamics, so called spin torque oscillation, in magnetic nano-contact MR element with a synthetic antiferromagnetic type spin-valve structure under high in-plane applied magnetic field of 0.9-1 kOe. Very high level oscillation of 18 nVHz-1/2 with narrow FWHM of 12 MHz was observed in the condition of negative applied current where electron-spin is injected from free layer to reference one. Applied current dependency on an oscillation frequency is a blueshift with good linearlity, and same dependency on level and FWHM is almost constant in the range of -10 to -14 mA, while applied field dependency on frequency shows redshift with two different slopes, -2.5 MHz/Oe in less than 1 kOe and -8.7 MHz/Oe in more than 1 kOe which field is smaller than the spin-flop field for the synthetic antiferromagnet, besides very clear and reasonable peak and bottom for oscillation level and FWHM are observed, respectively. It is thought that these magnetization dynamics are originated from synthetic antiferromagnet. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Dipolar Field Effect on Microwave Oscillation in a Domain-Wall Spin Valve

    Publication Year: 2009 , Page(s): 3422 - 3425
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (411 KB) |  | HTML iconHTML  

    In this paper, we examined dipolar field effects on the microwave generation in the domain-wall spin valve by solving simultaneously the Landau-Lifshitz-Gilbert and Zhang-Levy-Fert diffusion equations. By numerically analyzing dipolar field dependence, we showed that the microwave generation needs the dipole-dipole interaction for a 180deg domain wall and the amplitude of the microwave voltage signal depends strongly on the exchange length. In order to design a microwave generator using the domain-wall spin valve with high efficiency, we propose that the materials with short exchange length are preferred. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Temperature Dependence of Microwave Nano-Oscillator Linewidths Driven by Spin-Polarized Currents: A Micromagnetic Analysis

    Publication Year: 2009 , Page(s): 3426 - 3429
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    The dependence of the linewidth on the temperature in a spin valve driven by spin-polarized currents is analyzed by means of full micromagnetic simulations. The results are compared to the recent analytical predictions by Tiberkevic and confirmed by the experiments of Boone In agreement with the Tiberkevic theory and experiments of Sankey , our micromagnetic results point out two regimes. The linewidth increases linearly with the temperature until a threshold value, above which a square root dependence is observed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Microwave Oscillations of the Giant Magnetoresistive Element in a Magnetic Field Perpendicular to the Plane

    Publication Year: 2009 , Page(s): 3430 - 3433
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (511 KB) |  | HTML iconHTML  

    Applied voltage and magnetic field dependence of microwave oscillations have been studied for the giant magnetoresistive (GMR) element. In this experiment, a magnetic field is applied perpendicular to the plane of GMR films. It is found that the power spectral density (PSD) is less dependent on the direction of magnetic field and the resistance gap induced by the magnetic field corresponds to the rapid increase of PSD. Moreover, noise peaks are observed in a high frequency range (about 8 GHz or higher) when a magnetic field of more than 2000 Oe is applied. The peak frequencies shift to higher frequency as the magnitude of magnetic field increases. In contrast to a magnetic field, the peak frequencies and their widths are more susceptible to the direction of current. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Spin-Polarized Transport and Dynamics in Magnetic Tunneling Structures

    Publication Year: 2009 , Page(s): 3434 - 3440
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (556 KB) |  | HTML iconHTML  

    In the first part of this paper, we report a systematic study on the structural evolution under rapid thermal annealing and the corresponding transport properties in magnetic tunnel junctions (MTJs) with a crystalline MgO barrier. The results clearly indicate that high tunneling magnetic resistance can be achieved by annealing MTJs at a very short time, and it is directly related to the formation of (001) crystalline structures. In the second part, we report the spin dynamics in tunneling structure through direct electrical detection. A surprisingly large voltage generation in F/I/N and F/I/F junctions was observed, which is contradictory to the prediction from the standard spin-pumping theory. We proposed a theoretical formalism to study spin-pumping effects in ferromagnetic multilayer structures. The formalism can yield a remarkably clean physical picture of the spin and charge pumping in tunneling structures. The calculated values are consistent with experimental results. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Theory of Injection Locking for Large Magnetization Motion in Spin-Transfer Nano-Oscillators

    Publication Year: 2009 , Page(s): 3441 - 3444
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (226 KB) |  | HTML iconHTML  

    We study magnetization dynamics in spin-transfer devices subject to DC and microwave injected currents. When the frequency of the injected current is sufficiently close to the self-oscillation frequency of the device, phase-locking occurs. This phenomenon is theoretically studied by using Landau-Lifshitz equation with Slonczewski spin-torque term. By exploiting separation of time scales and using averaging technique, we derive equations which are applicable to the study of phase-locking for arbitrary large magnetization motion. The stability diagram in the (detuning, ac current)-plane is determined and it is shown that phase locking is hysteretic at sufficiently large ac currents. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Magnetic-Field-Driven Ferromagnetic Resonance in Spin-Transfer Devices

    Publication Year: 2009 , Page(s): 3445 - 3448
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (190 KB) |  | HTML iconHTML  

    An analytical approach to the study of ferromagnetic resonance in nanomagnets is discussed in the case when radio-frequency magnetic fields and spin-polarized electrical currents are simultaneously present. Current-controlled foldover effects in ferromagnetic resonance are predicted and analyzed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Measurement of Effective Free Layer Magnetization Orientation of TMR Sensors

    Publication Year: 2009 , Page(s): 3449 - 3452
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB) |  | HTML iconHTML  

    Measurements of thermal magnetization fluctuation noise spectrum in multi-directional magnetic field reveal tilt of effective free layer orientation in TMR sensors. We propose a method for effective sensor stiffness field measurement and demonstrate that deviations of stiffness from nominal values are caused by the angular dependence of the stiffness field. Ferro-magnetic resonance peak measurements indicate that the free layer magnetization orientation may be tilted from the cross-track direction. This magnetization tilt is caused by reference layer, hard bias problems and shape anisotropy effects. This reduces sensor efficiency and leads to amplitude asymmetry, multi-domain configuration and sensor instability. FMR-based method for detection of potentially unstable heads based on these observations is proposed. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Influence of Diffused Boron Into MgO Barrier on Pinhole Creation in CoFeB/MgO/CoFeB Magnetic Tunnel Junctions

    Publication Year: 2009 , Page(s): 3453 - 3456
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (332 KB) |  | HTML iconHTML  

    A relationship between boron (B) diffusion into the MgO barrier and pinhole creation in CoFeB/MgO/CoFeB-magnetic tunnel junctions (MTJs) was investigated. The diffused B in the MgO layer was identified by secondary ion mass spectrometry for the MTJs annealed at 350degC , which provide the giant magnetoresistance (TMR) ratio. The pinhole density, estimated from the statistic distribution of breakdown voltage of the TMR properties, increased as either the thickness or the B content of the CoFeB layer became thicker or higher. These experimental findings imply that the diffused B into the MgO barrier creates pinholes to short-circuit the tunnel conduction, since the amount of diffused B into the MgO barrier might be related to the total amount of the B content in the CoFeB layer. Three different techniques were found to be useful for the reduction of diffused B into the MgO barrier layer; usage of materials having boron affinity for capping layer, decrease of the total amount of B-content in CoFeB layer, and reduction of grain boundaries in the MgO barrier layer. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Influence of Boron Diffusion on Transport and Magnetic Properties in CoFeB/MgO/CoFeB Magnetic Tunnel Junction

    Publication Year: 2009 , Page(s): 3457 - 3459
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (606 KB) |  | HTML iconHTML  

    Influence of boron concentration in CoFeB on the transport properties of CoFeB (B 20% and B 16%)/MgO/CoFeB magnetic tunnel junction (MTJ) was investigated. Boron distribution was studied by using X-ray photoelectron spectroscopy (XPS). High-resolution transmission electron microscope was utilized for analysis of the texture and interface quality. The MTJ with the boron diluted CoFeB (B 16%) pinned layer shows 10% higher MR than the CoFeB (B 20%). HRTEM shows that the MgO/CoFeB interface for the sample with diluted CoFeB layer has a better epitaxial MgO/CoFeB growth. Higher boron concentration in the as-deposited CoFeB stays high after annealing but boron content in the MgO increases as well. These results suggest that that MR improvement is directly related to the distribution of the boron in CoFeB/MgO/CoFeB MTJs after annealing. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • High Bulk Spin Scattering Asymmetry in CPP Spin Valves With Alternated Monatomic [\hbox {Fe/Co}]_{\rm n} Superlattice

    Publication Year: 2009 , Page(s): 3460 - 3463
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (740 KB) |  | HTML iconHTML  

    We confirmed the structural properties of trilayered epitaxial films with AML [Fe/Co]n and Au spacer on Au electrode by RHEED and TEM. A considerably large DeltaRA (2.61 mOmegamum2) resistance area product was observed in all metallic current perpendicular-to-plane giant magneto-resistance (CPP-GMR) spin-valve elements by using alternate monatomic epitaxial [Fe/Co]n ferromagnetic layer with IrMn layer on the top. The estimated spin scattering asymmetry coefficient beta and interface asymmetry coefficient gamma was 0.81 and 0.43 plusmn 0.05, respectively. This value of beta is higher than that of Fe50Co50/Cu laminated with Cu spacer or Heusler alloy which is largest value ever reported at room temperature. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Effect of Buffer Layer Texture on the Crystallization of CoFeB and on the Tunnel Magnetoresistance in MgO Based Magnetic Tunnel Junctions

    Publication Year: 2009 , Page(s): 3464 - 3466
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (337 KB) |  | HTML iconHTML  

    Two different buffer layers (Ta/Ru/Ta and thick Ta) were tested for MgO MTJs. The influence of buffer layer texture on the crystallization of CoFeB bottom and top electrodes and on the tunnel magnetoresistance effect was investigated. X-ray results suggest that, after anneal, the CoFeB layer above MgO is well (200) textured and it does not depend on the buffer layer since MgO (100) barrier supplies a good template for CoFeB (200) orientation, while the crystallization of bottom CoFeB layer relies on the buffer layer texture. Different from Ta (110) found in Ta/Ru/Ta buffer layer, a thick Ta buffer layer has beta-(200) texture, which induces (001) oriented grains in MnPt layer. Because of the epitaxy relationship between MnPt and FeCo with MnPt(001)[100]//FeCo(200)[110], MnPt (001) oriented grains lead to the crystallization of bottom CoFeB layer with (200) orientation. As a result, higher TMR ratio up to 290% was achieved in the EB-MTJs with thick Ta buffer layer. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • MgO-Based Epitaxial Magnetic Tunnel Junctions Using Fe-V Electrodes

    Publication Year: 2009 , Page(s): 3467 - 3471
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (549 KB) |  | HTML iconHTML  

    To examine the influence of the barrier quality in fully epitaxial Fe/MgO/Fe(001) magnetic tunnel junctions (MTJs), we propose to use Fe-V alloys as magnetic electrodes. This leads to a reduced misfit with MgO. We actually observe, by high-resolution electron microscopy (HREM) and local strain measurements, that the misfit dislocations density in the MgO barrier is lower when it is grown on Fe-V(001). This improvement of the crystalline quality of the MgO barrier actually leads to a significant increase of the tunnel magneto-resistance (TMR), despite the loss of spin polarization (SP) in these alloys, which was measured by spin-polarized X-ray photoelectron spectroscopy (SR-XPS). View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Antiferromagnetic Coupling in Sputtered MgO Tunnel Junctions With Perpendicular Magnetic Anisotropy

    Publication Year: 2009 , Page(s): 3472 - 3475
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (289 KB) |  | HTML iconHTML  

    Antiferromagnetic coupling between magnetic electrodes has been observed in non-epitaxial perpendicularly magnetized MgO tunnel junctions. This coupling becomes less negative with increasing annealing temperature up to 375degC. This can be possibly related to homogeneization of oxygen in the barrier and de-oxidation of the magnetic electrodes. However, the evolution of coupling field with both barrier and electrode thickness doesn't agree with existing coupling theories. Similar structures with in-plane magnetized electrodes exhibit classical ferromagnetic coupling. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Perpendicular Magnetic Tunnel Junctions with CoFe/Pd Multilayer Electrodes and an MgO Barrier

    Publication Year: 2009 , Page(s): 3476 - 3479
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (243 KB) |  | HTML iconHTML  

    We studied the magnetic and magnetoresistance characteristics of pseudospin-valve magnetic tunnel junctions (MTJs) based on CoFe/Pd multilayer electrodes with perpendicular magnetic anisotropy and an MgO barrier. The MTJs at annealing temperature (T a) of 473 K showed a tunnel-magnetoresistance (TMR) ratio of 1.5%. An fcc (111)-oriented texture of the bottom and top Co90Fe10/Pd multilayer electrodes, together with an imperfectly crystallized MgO, were revealed by cross-sectional TEM images. The TMR properties of perpendicular MTJs with a Co20Fe60B20 or Co50Fe50 layer inserted between the CoFe/Pd multilayer electrodes and the MgO barrier were also studied. The TMR ratio with Co20Fe60B20 insertion was 1.7% at T a= 473 K and monotonically decreased at T a over 523 K. The TMR ratio with Co50Fe50 insertion increased up to 3% at T a= 573 K and then decreased to 0.4% at T a= 598 K. The influence of the Pd layer on CoFeB was studied by using the simplified structures of Pd/CoFeB/MgO/CoFeB/Pd and Ta/CoFeB/MgO/CoFeB/Ta with inplane anisotropy. A former structure with Pd resulted in reduced TMR ratio which decreases with increasing T a, whereas MTJs with a Ta-based structure showed a monotonic increase of a TMR ratio. The low TMR ratio observed in Pd-containing structures appears to result from crystallization of CoFeB in an unfavorable crystal orientation. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Magnetoresistance Properties of Planar-Type Tunnel Junctions With Ferromagnetic Nanogap System Fabricated by Electromigration Method

    Publication Year: 2009 , Page(s): 3480 - 3483
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (727 KB) |  | HTML iconHTML  

    We report electromigration techniques for the fabrication of planar-type tunnel junctions with ferromagnetic nanogap system. In these techniques, by monitoring the current passing through the devices, we are easily able to obtain the planar-type Ni-Vacuum-Ni tunnel junctions. In this paper, magnetoresistance (MR) properties of the planar-type Ni-based tunnel junctions formed by stepwise feedback-controlled electromigration (SFCE) and field-emission-induced electromigration (activation) are studied. We performed the SFCE method for Ni nanoconstrictions connecting asymmetrical butterfly-shape electrodes. Furthermore, the activation technique was applied to Ni nanogaps with separations of 15-45 nm. MR ratio of the devices formed by the SFCE exhibited approximately 4% at 16 K . On the other hand, the devices fabricated by the activation showed MR ratio of above 300% at 16 K. These results suggest that it is possible to fabricate planar-type ferromagnetic tunnel junctions with vacuum barriers by electromigration techniques. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Thermal Magnetic Noise From Synthetic Antiferromagnets in Magnetoresistive Heads

    Publication Year: 2009 , Page(s): 3484 - 3487
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (379 KB) |  | HTML iconHTML  

    Thermal magnetic noise in magnetoresistive read heads was studied extensively in recent years. It is believed that thermal magnetic noise is becoming the dominant noise source in read heads for hard-disk drive applications. Most previous work concentrated on magnetic white noise from free layers. This work shows that magnetic noise from a synthetic antiferromagnet can be comparable to that from a free layer in tunneling read heads for current and future hard-disk drives. An analytical model is established for thermal magnetic noise based on the single domain particle assumption. The model agrees well with results from a full micromagnetic model. This indicates that magnetic thermal fluctuations in current tunneling heads are close to being coherent. View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

IEEE Transactions on Magnetics publishes research in science and technology related to the basic physics and engineering of magnetism, magnetic materials, applied magnetics, magnetic devices, and magnetic data storage.

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Pavel Kabos
National Institute of Standards and Technology