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Synthetic antiferromagnetic particles with perpendicular magnetic anisotropy offer a highly desirable platform for use in fluidic applications. This work illustrates their high level of switching field tunability and demonstrates the ability to use particle design to overcome unfavorable hysteretic changes during patterning to manufacture functional, low switching field nanodisks. This makes them ideal candidates for lab-on-chip technologies such as microfluidic sorting or detection devices.

We report on the large-scale integration of graphene layers over a FePd perpendicular magnetic anisotropy (PMA) platform, targeting further downscaling of spin circuits. An L10 FePd ordered alloy showing both high magneto-crystalline anisotropy and a low magnetic damping constant, is deposited by magnetron sputtering. The graphene layer is then grown on top of it by large-scale chemical vapor deposition. A step-by-step study, including structural and magnetic analyses by x-ray diffraction and Kerr microscopy, shows that the measured FePd properties are preserved after the graphene deposition process. This scheme provides a graphene protected perpendicular spin electrode showing resistance to oxidation, atomic flatness, stable crystallinity, and perpendicular magnetic properties. This, in turn, opens the way to the generalization of hybrid 2D-materials on optimized PMA platforms, sustaining the development of spintronics circuits based on perpendicular spin-sources as required, for instance, for perpendicular-magnetic random-access memory schemes.

Perpendicular magnetic tunnel junctions (p-MTJs) with a MgO barrier and a 1-nm-thick MnGa electrode were investigated by inserting several monolayers (MLs) of Mn. The tunnel magnetoresistance (TMR) ratio systematically increased when increasing the Mn layer thickness with a maximum of 18 (38.4)% at 300 (5) K for a Mn layer thickness of 0.6–0.8 nm. This ratio is five times higher compared to that without the Mn layer. The perpendicular magnetic anisotropy (PMA) field and the PMA constant of the ultrathin MnGa layer also increased up to 62–90 kOe and 6.2–11.3 Merg/cm3, respectively, with an increase in the Mn interlayer thickness, even for the ultrathin regime of the MnGa layer. For p-MTJs showing a high TMR and PMA, electron microscopy indicated the presence of 3–4 MLs of Mn at the MnGa/MgO interface; thus, the Mn modification enhanced the TMR as well as improved the PMA. This may be a promising finding to develop a Mn-based free layer for spin-transfer-torque devices for high-recording-density magnetoresi...

The magneto-optical (MO) properties of perpendicular magnetic nanostructures consisting of a hexagonal close-packed Co80Pt20 nanolayer and noble-metal (Ag or Au) fine grains were investigated under polar Kerr measurement conditions. The samples exhibited an unusual MO hysteresis loop in which the Kerr rotation angle increased at a low magnetic field; this effect was observed in a different wavelength region for the CoPt–Ag and CoPt–Au samples. The nanostructures consisted of two magnetic regions of CoPt layers formed on the grains and on the underlayer. The increase in the Kerr angle was induced by the antiparallel magnetic alignment of these CoPt layers. The opposite MO polarity on the CoPt nanostructures was suggested in a micro-MO observation using scanning near-field polarized optical microscopy. The Ag and Au fine grains induced the MO phase reversal of CoPt in a different wavelength region for each sample. These MO behaviors were attributed to the influence of localized surface plasmons excited on the noble-metal grains. The magneto-plasmonic activities on the CoPt nanostructures were also affected by the underlayer material and the environmental conditions. The perpendicular magnetic nanostructures are expected to provide a new type of probe for chemical and biological sensing applications.

Free layers with double MgO/CoFeB interfaces are an established solution for improving the thermal stability at small device dimensions in perpendicular spin transfer torque-magnetic random access memory devices. A thin spacer layer, composed usually of Ta, W, Hf, etc., is used to ease crystallization and improve the perpendicular magnetic anisotropy. Here, we use ferromagnetic resonance to evaluate the impact of Ta or W containing spacer layers on the intrinsic anisotropy Hk and damping α parameters. While both spacer materials enable similar tunnel magneto-resistance and anisotropy values, W typically generates a higher damping. Ta-based spacers are therefore likely better candidates for very low switching current applications.

The ac losses at 20 and 30 Hz were measured for two disk-shaped YBa2Cu3O7 films in perpendicular peak applied magnetic fields up to ∼0.2 T in liquid nitrogen. One of the films had a significantly higher critical-current density than the other as determined from the loss measurements. Also, it exhibited a more-uniform flux penetration around the circumference of the disk than the other as observed by magneto-optical images of these films in perpendicular dc fields. The results from this film were compared with theoretical predictions of ac losses for disks of thin superconducting films in perpendicular magnetic fields using the Bean model [J. R. Clem and A. Sanchez, Phys. Rev. B 55, 9355 (1994)], and the Kim critical-current model [D. V. Shantsev et al., Phys. Rev. B 61, 9699 (2000)]. The asymptotic Bean model predictions for low and high fields were in reasonably good agreement with the data. The numerical calculation of the losses following Shantsev et al. was found to give extremely good agreement with the loss data throughout the entire field range of the measurement when the Kim model for the critical-current density was used.

An original approach to tune the ferromagnetic resonance frequency of a soft magnetic Ni80Fe20 (Permalloy = Py) film with in-plane magnetic anisotropy (IMA) based on the controlled coupling to a hard magnetic NdCox film with perpendicular magnetic anisotropy (PMA) through a nonmagnetic Al spacer is studied. Using the transverse magneto-optical Kerr effect (T-MOKE), alternating gradient magnetometry (AGM), and vector network analyzer ferromagnetic resonance (VNA-FMR) spectroscopy, the influence of both the Co concentration and the Al spacer thickness on the static and dynamic magnetic properties of the coupled IMA/PMA system is investigated. Compared to a single Py film, two striking effects of the coupling between IMA and PMA layers can be observed in their FMR spectra. First, there is a significant increase in the zero-field resonance frequency from 2.0 GHz up to 6.4 GHz, and second, an additional frequency hysteresis occurs at low magnetic fields applied along the hard axis. The maximum frequency difference between the frequency branches for increasing and decreasing magnetic fields is as high as 1 GHz, corresponding to a tunability of about 20% at external fields of typically less than ±70 mT. The origin of the observed features in the FMR spectra is discussed by means of magnetization reversal curves., D.M., D.S.S., and L.M.Á.-P. acknowledge financial support from INP of CNRS for a postdoc position, experimental equipment, and guest researcher stays, respectively. A.H.-R. acknowledges European Union's Horizon 2020 framework program for research and innovation under the Marie Skłodowska-Curie Action No. H2020-MSCA-IF-2016-746958. This work was supported by Spanish MINECO under Project No. FIS2016-76058 (AEI/FEDER, UE).

The ac losses in three disk-shaped YBa2Cu3O7 (YBCO) films, which were deposited on SrTiO3 by the pulsed-laser-deposition technique and had thicknesses, d, of 0.2, 1.0, and 3.0 μm, were measured in perpendicular applied ac magnetic fields to ∼0.14 T at 10 Hz in liquid nitrogen. The losses at low fields were found to be a strong function of the film thickness. The measured losses were compared with the theoretically calculated losses. The ac losses calculated using a field-independent critical-current density, the Bean model [J. R. Clem and A. Sanchez, Phys. Rev. B 50, 9355 (1994)], agreed very well with the 0.2-μm-thick film, while the calculated losses agreed well with the measured ones when a field-dependent critical-current density, the Kim model [D. V. Shantsev, Y. M. Galperin, and T. H. Johansen, Phys. Rev. B 61, 9699 (2000)], was used for the films of thickness 1.0 and 3.0 μm. However, a surprising discrepancy was found in the values of Bc and B0 for thinner YBCO films depending on whether they were ...

A method of calculation of rotation–vibration states for a general triatomic that places the body-fixed z axis perpendicular to the plane of the molecule is implemented within a discrete variable representation (DVR) for the vibrational motion. Calculations are presented for water and H3+. For H3+ the new method improves on previous high accuracy ab initio treatments of the rotation–vibration energies of the molecule both in accuracy and the range of rotational states that can be treated. Reliable treatment of quasilinear geometries means that the method is also promising for treating very highly excited states.

Stability of the sheared slab ηi mode at the tokamak internal transport barrier (ITB) off and near the minimum-q magnetic surface is studied under the assumption that the profile of the perpendicular rotation velocity has a Gaussian distribution. The results show that the effects of the perpendicular velocity profile with shear and curvature depend on the regimes with finite or weak magnetic shear where the ITB is located; on the rotation direction along the ion or electron diamagnetic drift; and on the mode structure of the eigen perturbation. The stabilizing or destabilizing roles of the perpendicular velocity shear and curvature are numerically analyzed in detail.

In this paper, we give an estimation of the longitudinal current in a tokamak due to high-energy minority ions obtained by perpendicular ICR heating. To illustrate this current, which is known as the banana-drift current, we give an estimation of this effect in an ITER-like tokamak. It is shown that by changing the number of accelerated minority ions, by selecting the position and energy of the resonant layer in which they are accelerated, it is possible to completely replace the noninductive current driven by other methods (for example, with RF power and high-energy neutrals beams). Thus, it is shown that the self-induced currents (bootstrap, asymmetry, and banana-drift currents) driving by continuous HF sources can provide steady-state operation of a fusion reactor.

Isomerization of HCN is studied numerically for a laser excitation configuration of two perpendicular intense IR pulses. This scheme confines the molecule to a plane and promotes proton transfer along the curved reaction path. It is shown that internal rotation of the CN group enhances isomerization when compared to a fixed C≡N orientation model. Isomerization rates with rotation exceed those without rotation of the CN by about a factor of 3. Internal rotation also enhances dissociation and destroys phase control of the isomerization. It is found that at intensities I∼1013 W/cm2, maximum isomerization occurs with negligible dissociation for a 2 ps pulse excitation. Maximum isomerization is also found for one field frequency resonant with the CH bend frequency ωbend and the other perpendicular frequency at 2ωbend.

We have measured the rate at which recorded signals decay in perpendicular Co78Cr17Ta5 alloys, Co70Cr15Ta5Pt10 alloys, and Pd/Co multilayers. At low write frequencies, the magnetization decay resembles that observed by magnetometry. At high write frequencies, the relative decay rate decreases substantially. This is attributed to a change in the demagnetizing energy associated with high linear densities in perpendicular media. A model for magnetization decay is used to deduce the activation volume, the size distribution, and the barrier to flux reversal which exists for the alloy films. A time scale te is introduced, over which the decay rate is dominated by the initial condition applied by the write head. The observed decay in the multilayers was much lower (

Ultrathin ferromagnetic films display a wealth of spectacular characteristics, one of which is that two-dimensional ferromagnetism is stabilized exclusively by magnetic anisotropies. In this work, we experimentally demonstrated the realization of ultrathin yttrium iron garnet (Y3Fe5O12) films with perpendicular magnetic anisotropy by pulsed laser deposition. A labyrinthine magnetic domain configuration in Y3Fe5O12 was identified by magnetic force microscopy, qualitatively determining that the magnetic moment possesses an out-of-plane component. Magnetic moments in the Y3Fe5O12 film were investigated by using a vibrating sample magnetometer and magnetic circular dichroism spectroscopy. Due to the surface sensitivity, the characterization technique based on magnetic circular dichroism spectroscopy presents as a high-resolution magneto-optical method to determine the magnetic property quantitatively, which has an advantage over the vibrating sample magnetometer technique commonly used for bulk crystals or powders, especially when the paramagnetic background from the supporting substrate is non-negligible. Our work introduces the burgeoning material synthesis and processing technology, and miscellaneous characterization techniques into the study of conventional magnetic oxide films, providing powerful supplements to the detection and modulation of magnetism at the nanoscale.

[Pt(1.5 nm)/Co(tCo)/W(1.5 nm)]N multilayers of different Co thicknesses (tCo) and number of repeats (N) have been grown by sputtering on Si substrates, and their magnetic properties have been studied. The x-ray reflectivity has been used to measure thicknesses of each layer as well as their roughness. The dependence of the magnetic moment on tCo and N (as determined by vibrating sample magnetometry) indicates the existence of a magnetic dead layer, which increases with N and reaches its maximum values for N ≥ 3. A similar N dependence of the magnetization at saturation is found. Ferromagnetic resonance and Brillouin light scattering have been used to investigate perpendicular magnetic anisotropy, damping, and interfacial Dzyaloshinskii-Moriya interaction (iDMI) vs Co thickness and the number of Pt/Co/W sequence repeats. We show that these parameters result from interface contributions that vary in a similar way with N, confirming that the first two Pt/Co/W trilayers are of lower quality. We thus conclude that for these systems, the increase of N improves the quality of interfaces and the volume of the stack, leading to the enhancement of the magnetic properties. Moreover, the measured weak iDMI constant, even for the higher N values, suggests that most probably, this iDMI results mainly from the Pt/Co interfaces.

The magnetization-curling mode in a columnar-structure film with perpendicular magnetization is studied on the assumption that the film is a two-dimensional array of cylinders. The angular dependence of the nucleation field HN is calculated by the Ritz method and compared with that for the coherent-rotation mode. It is found that the magnetization rotates in the curling mode for a large reduced radius S and in the coherent-rotation mode for a small S. The angular dependence of HN is different from that in an infinite cylinder. If S is large, the magnetization rotates in the curling mode for any value of θ0, where θ0 is the angle between the applied field and the cylinder axis. When S is medium, the magnetization rotates in the coherent-rotation mode for a small θ0 and in the curling mode for a large θ0.

Cobalt (Co) nanowire arrays were electrodeposited into the pores of polycarbonate membranes. A magnetic field parallel or perpendicular to the membrane plane was applied during deposition to control the wire growth. X-ray diffraction, transmission electron microscopy, and vibrating sample magnetometer were employed to investigate the structure as well as the magnetic properties of the nanowire arrays. The results show that the magnetic field applied during deposition strongly influences the growth of Co nanowires, inducing variations in their crystalline structure and magnetic properties. The sample deposited with the field perpendicular to the membrane plane exhibits a perpendicular magnetic anisotropy with greatly enhanced coercivity and squareness as a result of the preferred growth of Co grains with the c axis perpendicular to the film plane. In contrast, the deposition in a parallel magnetic field forces Co grains to grow with the c axis parallel to the film plane, resulting in in-plane anisotropy.

This article reports a sputtering system, the Intevac Superlattice Source (SLS), designed to meet the needs of making perpendicular multilayers for hard disk manufacturing. The SLS is a two-sided sputtering station in which each side is capable of depositing multiple sequential bilayers of two different film materials. Each side of the source contains a magnetron (sharing the same centerline as the substrate) and a rotating cathode on which are mounted two semicircular targets. The two rotating cathodes (one on each side of the source) are synchronized to ensure matched elements sputtering simultaneously and to prevent cross contamination between target materials. The design easily integrates onto standard hard disk manufacturing systems and can deposit up to 5 bilayers per second. Using this source, a series of Co/Pd multilayers has been made. We investigated the effect of different seedlayers, Pd, Ti, and Ru, on the coercivity and microstructure of Co/Pd multilayers. We found that although the crystalli...

Poisson’s equation is solved exactly to obtain the medium demagnetization field for both a single pole head and a single pole with a trailing shield (shielded single pole) head designs in perpendicular recording. To write an isolated transition, for the semi-infinite single pole head, head imaging can be neglected when calculating the demagnetization field. To the semi-infinite shielded single pole head, when the pole separation is reduced, perfect imaging from both the head and the soft magnetic underlayer is a good approximation.

Comparisons of magnetic anisotropy and switching behavior of CoCr‐based alloy and Co/Pd multilayer media were made using a vector vibrating sample magnetometer. Magnetic anisotropy energy was determined from angle‐dependent measurements of the transverse magnetization, using a simple approximate expression for transverse moment versus applied field and rotation angle. Switching behavior was deduced from hysteresis and angle‐dependent energy‐loss measurements. The multilayers were found to switch by curling and domain wall motion, while the Co78Cr17Ta5 and Co70Cr15Ta5Pt10 media were found to switch by nearly coherent (Stoner–Wohlfarth) rotation. Plasma oxidation of the multilayers was found to slightly reduce the amount of coupling, but degraded readback amplitude to a contact recording transducer.

C-SPIN, one of six centers of STARnet, a Semiconductor Research Corporation program - MARCO; DARPA; National Science Foundation [ECCS-1310338]

Tetragonally distorted FeCo-Ti-N films were prepared on a Rh(001) underlayer. Uniaxial perpendicular anisotropy was observed for FeCo-Ti-N films with a thickness of 23.5 nm, and the c/a lattice distortion reached 1.08. The anisotropy constant (Ku) was estimated to be a minimum of 0.57 MJ·m−3 (5.7 × 106 ergs·cm−3). These results show that the combination of Ti and N additive elements could be effective for inducing lattice distortion in FeCo-based alloys on a Rh under layer, and that the lattice distortion increases Ku.

Media with laminated [Fe(Ta,Ti,Nb)C/Ta]n=2–4 soft magnetic underlayers (SULs) were prepared, and the effect of lamination on spike noise was investigated. Cross-sectional transmission electron microscopy observation revealed that nanocrystalline layers, composed of α-Fe grains with three-dimensional random orientation, were physically separated by 2.5-nm-thick Ta layers. Laminated SULs had low coercivities, i.e., less than 0.2 Oe, when the total thickness of the SUL ranged from 200 to 400 nm and the thickness of each nanocrystalline layer was more than 50 nm. These low coercivities are probably due to magnetostatic interaction between adjacent nanocrystalline layers. The medium with a laminated SUL showed much lower spike noise than the medium with a single-layer SUL. It is thought that magnetostatic interaction can reduce the stray field from the SUL, and result in a decrease in spike noise.

We report a stack structure which utilizes an in-plane exchange-biased magnetic layer to influence the coercivity of the bottom CoFeB layer in a CoFeB/MgO/CoFeB perpendicular magnetic tunnel junction. By employing a thickness wedge deposition technique, we were able to study various aspects of this stack using vibrating sample magnetometer including: (1) the coupling between two CoFeB layers as a function of MgO thickness; and (2) the coupling between the bottom CoFeB and the in-plane magnetic layer as a function of Ta spacer thickness. Furthermore, modification of the bottom CoFeB coercivity allows one to measure tunneling magnetoresistance and resistance-area product (RA) of CoFeB/MgO/CoFeB in this pseudo-spin-valve format using current-in-plane-tunneling technique, without resorting to (Co/Pt)n or (Co/Pd)n multilayer pinning.

In this paper, we present a study on two and a half dimensional (2.5D) perpendicular magnetic recording (PMR) media consisting of dual hard magnetic recording layers (RL) with 1st or top RL1 used for conventional data storage and 2nd or bottom RL2 used for dedicated servo with lower linear densities or DC servo patterns with focus on the writability issue of the bottom servo layer (RL2). We demonstrate experimentally the feasibility to magnetically erase, write, and re-write RL2 by laser assist on a home built heat-assisted-magnetic-recording writing test system. Experimental data (by magnetic force microscopy measurements) show that the signal amplitudes of the pre-recorded magnetic patterns for both RL1 and RL2 decrease at almost the same rate with thermal erasure using scanning laser power (Pw) from 13 mW to 23 mW, clearly indicating equally effective laser heating and close temperature rise for RL1 and RL2 for far field laser heating with laser pulse duration in sub-μs and μs range. This is further verified by theoretical simulations of the thermal distribution and the temperature rise depth profile in dual layer media by laser heating. Simulations indicate very little temperature difference of less than 6 K (∼1% of maximum temperature rise) between RL1 and RL2 because the main mechanism of temperature rises in RL1 and RL2 is due to the effective thermal conduction from the top layers to lower layers. These experimental and theoretical study results could provide useful understanding and insights into servo writing methods of 2.5D PMR media.

The local remanence magnetization of perpendicular magnetic recording bit patterns has been quantified by scanning interference electron microscopy. When two coherent probes run across each bit, the interference image contrast changes periodically with a unit of h/e (h: Planck’s constant, e: electron charge). Our numerical analysis shows that the magnetic field effect on the image contrast is less than 1/1000 that of the magnetization under the experimental conditions. This allows the local remanence magnetization of the film to be determined accurately by averaging the periodic contrast change measured over repetitive bit patterns. From the interference image of bit patterns on a Co (0.4 nm)/Pt (1.2 nm)×18 layered film, a value of 1.4×10−8 T m was obtained as the product of the remanence and the film thickness.

Quantized magnetic disks consisting of an array of single domain Ni pillars with a density of 18 Gbits/in.2 were fabricated using nanoimprint lithography (NIL) and electroplating. The total disk area, limited by the NIL mold, is 4 cm×4 cm, leading to a total 45 Gbits. Magnetic force microscope (MFM) images show that all pillars 70 nm in diameter and 400 nm in height are single domain. The magnetostatic interaction between adjacent pillars is fairly strong. The pillars have an average switching field of 360 Oe and can be switched by a MFM tip with a large magnetic moment.

In this report, dysprosium substituted Ce1Y2Fe5O12 (Ce:YIG) thin films (Dy:CeYIG) with perpendicular magnetic anisotropy (PMA) are successfully deposited on silicon and silicon-on-insulator waveguides by pulsed laser deposition. The structural, magnetic, and magneto-optical properties of Dy:CeYIG films are investigated. We find that increasing dysprosium concentration leads to a decreased out-of-plane magnetic saturation field. Dy2Ce1Fe5O12 and Dy2Ce1Al0.4Fe4.6O12 thin films show PMA dominated by magnetoelastic effects due to thermal mismatch strain. These films further exhibit high Faraday rotation and low optical loss. Our work demonstrates that Dy substitution is an effective way to induce PMA in Ce:YIG thin films without compromising their magneto-optical figure of merit, making this material promising for self-biased transverse electric mode optical isolator applications.

The ac susceptibility (ACS) of an YBa2Cu3O thin film in a perpendicular ac magnetic field (Ha) from 0.22 to 30.8 G is measured as a function of temperature. The temperature dependence of the real (χ′) and imaginary (χ′′) parts of the ACS for various Ha can be well scaled onto a single curve using the peak value (χp″) and temperature (Tp) of χ′′(T) as the scaling parameters. The scaling law suggests that the critical state can be established only below Tp. Above Tp, the ACS is determined by the screening effect of the film due to the sharp decrease of its resistance. Below Tp, the scaling behavior is in agreement with the theoretical approaches based on the critical state model, only if the temperature for zero critical current density is related to the irreversibility temperature Tirr rather than Tc. From the scaling law, we found that Tirr=Tp.

We compare for permalloy (Py)/Cu/Py or Py/Ag/Py exchange-biased spin valves, hysteresis loops of: (1) giant magnetoresistance (GMR) with current perpendicular to the layer planes (CPP-MR), and (2) magnetization M measured for the same portion of the sample used to measure the CPP-MR. As expected, the two kinds of loops are mostly very similar. There are, however, some slight differences, the source of which is not yet clear.

We have investigated the perpendicular magnetic field dependence of Josephson current through Nb/Al-AlOx/Nb junctions by applying a magnetic field in a direction perpendicular to the plane of the junction. We found hysteresis in the modulation characteristics of the Josephson current when a strong perpendicular magnetic field was applied to the Josephson junction. We have now measured the three-dimensional magnetic field dependence of the Josephson current by applying magnetic fields Hx and Hy in the direction parallel to the plane of the junction and magnetic field Hz in the direction perpendicular to the plane of the junction. When the perpendicular magnetic field Hz was applied to the Josephson junction, the main peak of the Fraunhofer pattern shifted from the origin of the (Hx and Hy) plane. We investigated why Josephson current is modulated by a perpendicular magnetic field Hz.

A fast bolometer was used for direct measurements of parallel electron energy flux in the edge of the Texas Experimental Tokamak (TEXT‐U) [K. W. Gentle, Nucl. Technol. Fusion 1, 479 (1981)]. The fluctuating component of the parallel electron energy flux, combined with a measurement of magnetic fluctuations, provides an upper limit to the perpendicular electron flux. This magnetically driven energy flux cannot account for the observed energy flux.

It has been suggested by various authors over the past 15 years, and also recently, that in tokamaks the perpendicular resistivity η⊥ is between 102 and 103 times the parallel (Spitzer) resistivity. Here it is shown that on the contrary the measurements on the FTU tokamak [Proceedings of the 16th Symposium on Fusion Technology, London, 1990 (North‐Holland, Amsterdam, 1991), Vol. 1, p. 218] are consistent with η⊥/η∥=2 when the extended neoclassical theory is used (which is preferable to the conventional neoclassical theory for reasons which are here reviewed).

The origin of the focused single-pulse laser irradiation-induced changes in magnetic anisotropy of a Pt/Co/Pt film is investigated by the x-ray absorption near-edge structure and extended x-ray absorption fine structure techniques combined with the photoelectron emission microscope. A significant increase of the Co–Co bond length in both in-plane and out-of-plane directions is observed on the periphery of the laser spot, at which perpendicular magnetization appears. With increasing laser power density towards the center of the laser spot, anisotropic structural changes are observed accompanied by the reappearance of in-plane magnetization. The enhancement of perpendicular magnetization is attributed to the lattice expansion-induced magnetoelastic effect, while the in-plane compressive strain in the Co film is suggested to be the origin of the reappearance of in-plane magnetization at higher laser power densities.

A new laser geometry, recently demonstrated, is analyzed. The laser cavity consists of two orthogonally oriented diffraction gratings faced by two plane boundaries, such as cleaved facets. It is shown that such lasers may operate at a single, very high mode order with excellent modal discrimination.

Magnetism control has a variety of applications in magnetic storage and spintronic devices. Instead of the control of direct magnetoelectric coupling via strain, voltage, and Dzyaloshinskii-Moriya interaction, the polarization-dependent coupling in multiferroic materials such as BiFeO3 is employed for the electric-field control of magnetizations in this work. A perpendicular magnetic anisotropy (PMA) has been realized in a BiFeO3/Al2O3/Pt/Co/Pt multiferroic structure at room temperature. Interestingly, a distinct change of coercivity field (∼400%) has been observed in the structure with opposite polarization directions, which can be attributed to the different oxidation degree at the Pt/Co interface. This spontaneous polarization-controlled switching not only provides us a platform to study the interfacial effect in multiferroic heterostructures but also paves the way to manipulate PMA or even spin orbit torque through oxygen vacancies.

We report the tunable separation of four distinct resistance levels in dual spin valves (DSV) with perpendicular magnetic anisotropy based on Co/Pd and CoFe/Pd multilayers. An optimal giant magnetoresistance (GMR) of 15.2% in the current in-plane geometry was obtained. By varying the spin filter layer thicknesses at the interfaces of one Cu spacer layer from 2 to 6 A, a linear dependence of GMR across the selected spacer layer was demonstrated without affecting the GMR contribution across the second Cu spacer layer in the DSV. Using this strategy, the intermediate resistance levels in a four-state perpendicular DSV can be adjusted independently, thus creating flexible platform for multistate storage.

Isolated output pulse shapes are calculated for magnetoresistive gradiometer read heads having various geometric and magnetic parameters. The two‐dimensional finite‐element and reciprocity methods are used. The ferromagnetic shield has a big effect on the pulse shape, especially for closely spaces shields. High shield reluctance causes pulse broadening and large positive tails. Addition of a medium underlayer decreases the pulse undershoots and increases pulse amplitude. A reluctance model is given that explains most of the observed effects on pulse shapes and illustrates the importance of reluctance balance to achieve optimum pulse shape.

We present an analysis of the extendability of traditional perpendicular recording based on micromagnetic recording simulation and channel cost/performance analysis. The analysis indicates that head field gradient is the single most important factor in realizing densities above 1.0 Tb/in2. The conclusion of this analysis is that 1.5 Tb/in2 may be possible with this technology, but 2 Tb/in2 will be extremely challenging, perhaps impossible even with powerful channel chips. We also examine the extendibility of servo systems, and conclude that either actuator bandwidth must be increased by a factor of 2 from today’s drives or integrated disturbance power spectrum must be decreased by a factor of 2 to reach densities of 2 Tb/in2 and beyond.

Spin torque switching is investigated in perpendicular magnetic tunnel junctions using Ta∣CoFeB∣MgO free layers and a synthetic antiferromagnet reference layer. We show that the Ta∣CoFeB interface makes a key contribution to the perpendicular anisotropy. The quasistatic phase diagram for switching under applied field and voltage is reported. Low switching voltages, Vc 50 ns=290 mV are obtained, in the range required for spin torque magnetic random access memory. Switching down to 1 ns is reported, with a rise in switching speed from increased overdrive that is eight times greater than for comparable in-plane devices, consistent with expectations from a single-domain model.

A dot-by-dot analysis to investigate the magnetization switching behavior of the perpendicular patterned CoCrPt medium is reported. The medium is investigated by in situ and ex situ magnetic force microscopy (MFM) techniques. The topographical and magnetic characteristics of each magnetic dot were studied in given areas. The perpendicular dc demagnetization (DCD) remanence data evaluated by counting the volume of reversed magnetic dots according to the ex situ MFM measurements were in good agreement with alternating gradient magnetometry measurements. The influence of the magnetostatic energy associated with nanodots to the distribution of the intrinsic coercivity of individual magnetic dots and the intrinsic DCD curve of the medium are estimated. Further, the mechanism of magnetization reversal of individual magnetic dot is discussed.

We present a bimodal magnetic force microscopy sensor consisting of a conventional cantilever beam, a spacer element, and an iron-filled carbon nanotube. Depending on the mode of the cantilever's resonant flexural vibration, the sensor is sensitive to magnetic field derivatives parallel and perpendicular to the sample's surface. This multifunctionality is supported by the scalar-type behavior of the magnetic monopole-like end of the iron-filled carbon nanotube.

An excimer-laser-crystallized polycrystalline-silicon silicon-oxide-nitride-oxide-silicon thin-film transistor with recessed-channel structure has been designed to achieve only one grain boundary with a protrusion perpendicular to the channel for investigating the grain boundary location effects on the memory characteristics. After programming, the devices demonstrated better memory characteristics as the grain boundary was allocated near the source junction. In contrast, the memory characteristics were degraded when the grain boundary was located near the drain junction. The phenomenon was explained by the 2-D device simulation and the energy band diagrams.

We performed high field torque magnetometry measurements on CoO/[Co/Pt] magnetic multilayers that exhibit perpendicular exchange bias. We find that the antiferromagnet CoO layers strongly modify the uniaxial anisotropy of the multilayer structures. The strongest effects due to the CoO layers occur in the vicinity of the Neel temperature, where we observe a suppression of the first-order anisotropy and a smaller enhancement of the second-order anisotropy. This results in a nonmonotonic variation of the anisotropy with temperature and for selected samples a transition from perpendicular to in-plane and back to perpendicular anisotropy with increasing temperature.

We have studied spin transfer switching (STS) in a magnetic tunnel junction with perpendicular magnetic anisotropy for the reference and free layers using the Landau–Lifshitz–Gilbert formalism. We propose a multilayer structure in which the insertion of an additional spin polarizer with in-plane anisotropy can enhance the STS efficiency and switching speed of the device. It is revealed that a canted spin polarizer with an angle between 40° and 80° out of the film plane in the correct direction enhances the STS efficiency more than a fixed in-plane or perpendicular polarizer. Furthermore, we show that the spin transfer torque exerted on the in-plane polarizer layer by the free layer automatically tilts the in-plane polarizer in the direction that enhances STS for both magnetization states of the free layer.

We present direct link between the transport properties of Co2MnSi and Co2FeMnSi Heusler based current-perpendicular-to-plane spin valves (CPP-SVs) and interface atomic structures resolved by aberration-corrected electron microscopy. The structure of the Co2FeMnSi electrodes is L21 but their interface with the CoSi spacer is disordered. In contrast to the Co2FeMnSi-electrodes, the Co2MnSi-electrodes have abrupt interfaces with the Ag spacer though their ordering is not fully L21. The magnetoresistance of the Co2MnSi-SV is over two orders of magnitude better than those of Co2FeMnSi-SV, demonstrating that the atomic interface ordering is crucial for the enhancement of the magnetoresistance in the Heusler CPP-SVs.

We show that adding a perpendicular polarizer to a conventional spin torque memory element with an in-plane free layer and an in-plane polarizer can significantly increase the write speed and decrease the write energy of the element. We demonstrate the operation of such spin torque memory elements with write energies of 0.4 pJ and write times of 0.12 ns.

Three-dimensional write field distributions of trailing-edge shielded and unshielded perpendicular write heads with applied direct current write currents were studied by magnetic force microscopy (MFM) measurements. A quantitative MFM approach of two times integrating measured frequency shift at a series of tip scan heights over the perpendicular direction was proposed to measure the magnetic field strength and field gradient. Results indicate shielded heads in addition to smaller saturation write currents, exhibited more than two to three times higher write field gradients over a wide range of moderate field strength over unshielded heads, thus, producing sharper bit transition and improved signal to noise ratio as theoretically predicted.

Electron holographic observations were performed in order to clarify the magnetic domain structures in nanosized pole tips for perpendicular recording heads made from Ni–Fe and Co–Ni–Fe. While an external magnetic field was applied, the magnetic fields leaking from the pole tips as well as the detailed magnetic flux distribution inside them were visualized for the first time. In addition, we report the direct observation result that implies the pole erasure characteristic of the Co–Ni–Fe pole tip. The observations have revealed that electron holography provides useful information for understanding the magnetic characteristics of nanosized pole tips for perpendicular recording heads.