Longitudinal Magnetic Anisotropy Research Articles

Obtaining extremely low coercivity of high Bs FeCoBSiCPCu nanocrystalline alloys through modulation of magnetic anisotropy

Longitudinal magnetic field annealing is utilized for modifying the magnetic anisotropy and enhancing the magnetic softness of Fe75Co8(B10Si3C3P1)1-x/17Cux (x = 0.5, 0.75, 1, 1.25) nanocrystalline alloys. All of the magnetic field-annealed nanocrystalline alloys with Cu content more than 0.5 at.% exhibit significantly improved soft-magnetic properties, including high saturation magnetic flux density up to 1.87 T, effective permeability of 13,000–16,000 under the condition of 1 A/m and 1 kHz, coercivity as low as 1.6 A/m, and core loss of 0.11–0.45 W/kg under the condition of 1.0 T and 50 Hz. The application of a magnetic field promotes the nucleation and inhibits the growth of grains, leading to an increase in the number density of nanocrystals and the crystalline volume fraction, and a reduction in the grain size. The magnetic field annealing reduces the effective magneto-crystalline anisotropy energy to 2–4 J/m3, and induces longitudinal magnetic anisotropy with anisotropy energy density of 400–900 J/m3 which shows dependence on the crystalline volume fraction. The field-induced magnetic anisotropy dominates over the random local magnetic anisotropies, and results in the formation of regular magnetic domains aligned longitudinally, pinning-free domain wall displacement, and thus enhanced soft-magnetic properties.

Effect of dopants on magnetic and magnetoimpedance properties of rapidly solidified FeCoBM (M = Al, Cu and Si) ribbons

In this work magnetic properties, magnetoimpedance (MI) and field sensitivity (η) of rapidly solidified (Fe0.7Co0.3)80B19M1 (M = B, Al, Si & Cu) ribbons have been investigated in the frequency range 0.5 – 13 MHz. Present study shows replacement of boron (B) by a nonmagnetic element (Al, Si or Cu) can alter the thermal stability, soft magnetic and magnetoimpedance properties of the (Fe0.7Co0.3)80B20 ribbons. It is found that saturation magnetization reaches the largest value for Cu-containing sample and the smallest value for Al-containing sample. The MI studies show maximum MI ratios 30% at 5 MHz, 23% at 7 MHz, 26% at 3 MHz and 39% at 4 MHz for M = B, Al, Si & Cu respectively. Variation of MI with external magnetic field shows single peak behavior of Al-content ribbon over the entire frequency range, whereas for all other samples single peak converted to double peak at higher frequency, which indicates existence of stronger longitudinal magnetic anisotropy in Al-containing ribbon. The MI variation with magnetization, M and damping constant, α is also validated through numerical simulations using standard electrodynamics models. Present study reveals that the variations of MI response are associated with formation of soft magnetic phase and development of anisotropy with replacement of B by an additional element.

Perpendicularly magnetized Co/Pd-based magneto-resistive heterostructures on flexible substrates.

Flexible magneto-resistive heterostructures have received a great deal of attention over the past few years as they allow for new product paradigms that are not possible with conventional rigid substrates. While the progress and development of systems with longitudinal magnetic anisotropy on non-planar substrates has been remarkable, flexible magneto-resistive heterostructures with perpendicular magnetic anisotropy (PMA) have never been studied despite the possibility to obtain additional functionality and improved performance. To fill this gap, flexible PMA Co/Pd-based giant magneto-resistive (GMR) spin-valve stacks were prepared by using an innovative transfer-and-bonding strategy exploiting the low adhesion of a gold underlayer to SiOx/Si(100) substrates. The approach allows overcoming the limits of the direct deposition on commonly used polymer substrates, whose high surface roughness and low melting temperature could hinder the growth of complex heterostructures with perpendicular magnetic anisotropy. The obtained PMA flexible spin-valves show a sizeable GMR ratio (∼1.5%), which is not affected by the transfer process, and a high robustness against bending as indicated by the slight change of the magneto-resistive properties upon bending, thus allowing for their integration on curved surfaces and the development of a novel class of advanced devices based on flexible magneto-resistive structures with perpendicular magnetic anisotropy. Besides endowing the family of flexible electronics with PMA magneto-resistive heterostructures, the exploitation of the results might apply to high temperature growth processes and to the fabrication of other functional and flexible multilayer materials engineered at the nanoscale.

Controllable magnetic anisotropy and magnetostriction constant in palladium cobalt alloy films: Effects of composition, thickness, and stress

The magnetic anisotropy of sputter-deposited films of palladium cobalt Pd100 − xCox (x = 7, 15, and 28 at. %) alloy is investigated systematically. The exact anisotropy energies of all contributions, namely, surface, magnetocrystalline, magnetoelastic, and shape, are estimated. Using these energies, the main origin of the magnetic anisotropy is determined and summarized in maps of film thickness and film stress. Consequently, how composition, thickness, and stress affect the magnetic anisotropy is clarified. Accordingly, the controllability between longitudinal and perpendicular magnetic anisotropy is revealed. In addition, the magnetostriction constant λ111 is estimated from the change in the volume anisotropy energy due to the stress in the film, namely, the inverse magnetostrictive effect. The constant is a large negative number, −178 ppm at maximum, and agrees partially with a reference value measured under normal magnetostriction. The disagreement by 30% of the magnetostriction constant with respect to the expected value for Pd72Co28 films was elucidated by the magnetostriction enlargement by tensile stress.

A Comparative Study of Magnetic Properties of Large Diameter Co Nanowires and Nanotubes.

A comparative study of the magnetic properties of the arrays of Co nanowires and nanotubes with large external diameters (180 nm) has been carried out. The nanowires/nanotubes were grown by electrodeposition into the self-assembled pores of anodic alumina membranes. The experimental study of their magnetic behavior was focused on the angular dependence of hysteresis loops and their parameters. In both nanowire and nanotube arrays, from the analysis of experimental data, effective longitudinal magnetic anisotropy is concluded, which is stronger in the case of the nanotube array. In addition, the extremely small remanence observed for all loops indicates the important role played by magnetostatic interactions. Micromagnetic simulations were first performed considering intrinsic shape and magnetocrystalline anisotropy terms, together with an effective easy-plane anisotropy to account for those magnetostatic interactions. A qualitative agreement between experiments and simulations is found despite the complexity introduced by the intrinsic and extrinsic array properties (i.e., large diameters, grain structure, and array configuration). In addition, simulations were also carried out for individual nanowire/nanotube with a particular emphasis to understand their differences at the remanence, due to pure geometry contribution.

Magnetoelastically induced magnetic anisotropy transition in [CoO5nm/CoPt7nm]5 multilayer films

The magnetic anisotropy transition of [CoO5nm/CoPt7nm]5 multilayer film with respect to post-annealing has been studied systematically. It undergoes a smooth transition from longitudinal magnetic anisotropy (LMA) to perpendicular magnetic anisotropy (PMA) upon annealing and returns backward to LMA at high temperature of 550°C. The strongest PMA of [CoO5nm/CoPt7nm]5 is achieved after post-annealing at 300°C and the tolerable post-annealing temperature with strong PMA is up to 400°C, which indicates this multilayer film could be a potential candidate for the PMA application at middle-high-temperature-region between 300°C and 400°C. The mechanism responsible for the transition of magnetic anisotropy has been investigated by analyzing CoO/CoPt interface and CoPt layer internal stress. It is found the effective PMA energy is proportional to the in-plane tensile stress of CoPt layer but is inversely proportional to the roughness of CoO/CoPt interface. Finally, by means of low temperature experiment we demonstrate the magnetic anisotropy transition observed in [CoO5nm/CoPt7nm]5 multilayer film is mainly attributed to the change of CoPt layer in-plane tensile stress.

Enhanced Perpendicular Magnetic Anisotropy of Co-Rich Type Co–Pt Film by Inserting Pt Underlayer

The Co-rich type Co–Pt alloy thin films were deposited on various thicknesses of Pt underlayer ( $t_{\mathrm {Pt}}$ ) on glass substrates at room temperature. It was observed that the magnetic properties, microstructures, and phase structures of Co–Pt films were significantly affected by Pt(111) underlayer. At $t_{\mathrm {Pt}} = 5$ nm, very small Pt grains induced multiple orientations in Co–Pt films, and then showed the longitudinal magnetic anisotropy (LMA). At $t_{\mathrm {Pt}} = 10$ nm, columnar Co–Pt grains with hcp(002) orientation grew on a single Pt(111) grain, leading $c$ -axis to be normal to the plane. The perpendicular magnetic anisotropy (PMA) of the film was enhanced. Further increase the $t_{\mathrm {Pt}}$ above 20 nm, Co–Pt grains exhibited hcp(100) orientation and the LMA is dominated again. In this paper, strong relationship between microstructures and magnetic properties in Co–Pt/Pt bilayer films was observed. The enhanced PMA in the Co–Pt/Pt bilayer film at $t_{\mathrm {Pt}} = 10$ nm is due to the existence of the column-like structure and strong hcp(002) orientations.

Influence of Debubbling on Crystal Structure and Magnetic Properties of Electrodeposited CoNiP Layers

Various stirring methods, including a magnetic stirrer, nitrogen bubbling, and ultrasonic stirring, were investigated to debubbling hydrogen during electrodeposition of $25~\mu \text{m}$ -thick Co76Ni18P6 layers on copper. Microstructure observation shows that a lot of hillocks form on the surface of Co–Ni–P films when using magnetic stirring. While a smooth surface morphology was obtained for those using nitrogen bubbling and ultrasonic stirring. This manifests effective depriving of hydrogen during electrodeposition with the later two stirring methods. All Co–Ni–P layers exhibit the coexistence of hexagonal closed packing (HCP) and face-centered cubic phases. The films obtained using magnetic stirring have a random crystalline orientation and longitudinal magnetic anisotropy showing intrinsic coercivity ( $H_{\mathrm {ci}}$ ) 1.45 kOe and remanence ( $M_{r}$ ) 7.7 kG. Nitrogen bubbling bestows Co–Ni–P layers a rather strong HCP (002) texture, which leads to the enhanced perpendicular magnetic anisotropy showing out-of-plane $H_{\mathrm {ci}}~2.65$ kOe and $M_{r}$ 1.9 kG. On the other hand, samples deposited using ultrasonic stirring have a relatively weak HCP (002) texture, and thus the magnetic behavior is longitudinal. Ultrasound vibration induces local heating and cavitation on the electroplating surface leading to the deteriorated (002) texture and surface roughening than that of the nitrogen bubbling.

Nanocrystalline Soft Magnetic (Fe<sub>0.7</sub>Co<sub>0.3</sub>)<sub>88</sub>Hf<sub>2</sub>W<sub>2</sub>Mo<sub>2</sub>Zr<sub>1</sub>B<sub>4</sub>Cu<sub>1</sub> Alloy with Enhanced Thermal Stability of Magnetic Properties

Magnetic properties, structure and thermal stability of the (Fe0.7Co0.3)88Hf2W2Mo2Zr1B4Cu1 alloy ribbon after its nanocrystallization at 620-750°C for 0-20 min in the presence or absence of tensile stresses σ were studied. It was shown that under the effect of tensile stresses a longitudinal magnetic anisotropy with an easy magnetization axis parallel to the long size of the ribbon was induced in the alloy. A better thermal stability of magnetic properties was observed for the alloy subjected to the nanocrystallization annealing at 620° for 20 min with σ = 170 MPa. After the subsequent annealing at 570°C for 25 h without σ, the magnetic properties of the alloy are unchanged. Increasing of the nanocrystallization annealing temperature up to 670-750°C did not result in improvement of the thermal stability of magnetic properties.

ChemInform Abstract: Observing Magnetic Anisotropy in Electronic Transport Through Individual Single‐Molecule Magnets.

ChemInformVolume 46, Issue 23 Reviews ChemInform Abstract: Observing Magnetic Anisotropy in Electronic Transport Through Individual Single-Molecule Magnets. E. Burzuri, E. Burzuri Kavli Inst. Nanosci., Delft Univ. Technol., NL-2600 GA Delft, Neth.Search for more papers by this authorR. Gaudenzi, R. Gaudenzi Kavli Inst. Nanosci., Delft Univ. Technol., NL-2600 GA Delft, Neth.Search for more papers by this authorH. S. J. van der Zant, H. S. J. van der Zant Kavli Inst. Nanosci., Delft Univ. Technol., NL-2600 GA Delft, Neth.Search for more papers by this author E. Burzuri, E. Burzuri Kavli Inst. Nanosci., Delft Univ. Technol., NL-2600 GA Delft, Neth.Search for more papers by this authorR. Gaudenzi, R. Gaudenzi Kavli Inst. Nanosci., Delft Univ. Technol., NL-2600 GA Delft, Neth.Search for more papers by this authorH. S. J. van der Zant, H. S. J. van der Zant Kavli Inst. Nanosci., Delft Univ. Technol., NL-2600 GA Delft, Neth.Search for more papers by this author First published: 22 May 2015 https://doi.org/10.1002/chin.201523284AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume46, Issue23June, 2015 RelatedInformation

Magnetic properties, thermal stability, and structure of soft magnetic (Fe0.7Co0.3)88Hf2W2Mo2Zr1B4Cu1 alloy that underwent high-temperature nanocrystallization

The effect of the temperature of nanocrystallizing annealing (NA) at temperatures of 670–750°C on the magnetic properties, structure, and thermal stability of the (Fe0.7Co0.3)88Hf2W2Mo2Zr1B4Cu1 alloy has been studied. The NA was performed both in the presence of tensile stresses applied to samples and in the absence of stresses. It was found that the nanocrystallization of the alloy under applied tensile stresses induces the longitudinal magnetic anisotropy with an easy magnetization axis parallel to the long side of the ribbon. The optimum conditions for nanocrystallization of the alloy, which stabilize its magnetic properties at a fairly high temperature of 570°C, have been determined.

Giant magnetoimpedance effect enhanced by thermoplastic drawing

We performed thermoplastic forming (TPF) on FeCoNbB metallic glass ribbons with a supercooled liquid region exceeding 100 K, and found the sample after TPF is still completely amorphous. More importantly, the giant magnetoimpedance (GMI) effect was improved after the forming process: the maximum GMI ratio and sensitivity increased from 41% to 12.3%/Oe in the case of as-cast sample to 280% and 358.2%/Oe in the case of resulting sample after TPF, respectively. The hysteresis loops and domain patterns were subsequently studied, which revealed that the primary factor leading to the improvement of the GMI effect was the enhanced longitudinal magnetic anisotropy induced by the TPF process. We therefore assume that TPF is an effective way that improves the GMI effect, which differs from conventional annealing methods.

Magnetic properties, thermal stability, and structure of the nanocrystalline soft magnetic (Fe0.7Co0.3)88Hf2W2Mo2Zr1B4Cu1 alloy with induced magnetic anisotropy

The effect of magnitude of tensile stresses (σ) applied to the (Fe0.7Co0.3)88Hf2W2Mo2Zr1B4Cu1 alloy with refractory-metal additions during its nanocrystallization at 620°C for 20 min on the magnetic properties, structure, and thermal stability of the alloy is studied. It has been found that, during the nanocrystallization of the alloy under the effect of tensile stresses of 6–250 MPa, longitudinal magnetic anisotropy with an easy magnetization axis parallel to the long size of ribbon is induced in the alloy. The thermal stability of magnetic properties of the alloy under study has been shown to be determined by the thermal stability of induced magnetic anisotropy and to depend on the magnitude of tensile stresses applied during nanocrystallizing annealing (NA). The better thermal stability of magnetic properties has been observed for the alloy subjected to NA at σ = 170 MPa. After annealing at 570°C for 25 h, the magnetic properties of the alloy are unchanged.

Induced magnetic anisotropy features in FeCrSiBNbCu nanocrystalline alloy: Role of stress distribution proven by direct X-ray measurements

Fe73.5−xCrxSi13.5B9Nb3Cu1 (x=1, 2, and 3) amorphous ribbons were prepared by single roller rapid quenching technique. Both conventional and stress annealing at 520°C for 2h at the value of the specific load of 150MPa resulted in the formation of a nanocrystalline structure with average grain size about 13nm. No significant differences in crystallite size were observed for all samples under consideration. The crystallite orientations were practically isotropic indicating no texture in the samples of all types. For all conventionally annealed ribbons a longitudinal effective magnetic anisotropy with an easy magnetization axis parallel to the ribbon axis was observed. For all stress annealed ribbons a transverse induced magnetic anisotropy with the anisotropy constant value of about 1800±50J/m3 was evident. Induced magnetic anisotropy features in FeCrSiBNbCu nanocrystalline alloy, namely an importance of the stress distribution was proven by direct X-ray measurements. A very good correlation between the induced magnetic anisotropy constant values and anisotropic stress distribution was observed.

Fe- and co-based nanocrystalline soft magnetic alloys modified with Hf, Mo, and Zr: Magnetic properties, thermal stability, and structure. Alloy (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1

The alloy (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1 is studied to obtain materials with improved thermal stability. The effect of the nanocrystallization conditions that occur during heat treatment (HT) and thermomechanical treatment (TMechT) in air at temperatures of 520–620°C on the structure of the alloy, as well as its magnetic properties and their thermal stability, is considered. Longitudinal magnetic anisotropy is shown to be induced in the alloy in the course of TMechT; the easy magnetization axis of the anisotropy is parallel to the long side of the ribbon. The alloy specimens subjected to heat and thermomechanical treatment have different magnetic characteristics. The (Fe0.7Co0.3)88Hf4Mo2Zr1B4Cu1 alloy is found to surpass the (Fe0.6Co0.4)86Hf7B6Cu1 and (Fe0.7Co0.3)88Hf7B4Cu1 alloys studied in [1] in the thermal stability of the magnetic properties. The magnetic properties of the alloy after nanocrystallization, which occurs in the course of TMechT (σ = 250 MPa) at 620°C for 20 min, hardly change during annealing at 550°C for 26 h.

Fe- and co-based nanocrystalline soft magnetic alloys modified with Hf, Mo, and Zr: Magnetic properties, thermal stability, and structure. Alloys (Fe0.6Co0.4)86Hf7B6Cu1 and (Fe0.7Co0.3)88Hf7B4Cu1

Nanocrystalline alloys (Fe0.6Co0.4)86Hf7B6Cu1 and (Fe0.7Co0.3)88Hf7B4Cu1 have been investigated to obtain materials with improved thermal stability and new features. In order to make the alloys produced by melt quenching on a rotating wheel nanocrystalline, they have been subjected to heat (HT) and thermomechanical (TMechT) treatments. The effect of HT and TMechT conditions on the magnetic properties, thermal stability, and structure of the alloys has been studied. The optimal HT conditions for obtaining the minimum values of the coercive force (Hc) in the alloys have been determined. It is shown that TMechT of the alloys leads to the induced longitudinal magnetic anisotropy with the axis of easy magnetization along the long side of the ribbon in the studied temperature range of 520–620°C. It has been established that the alloys (Fe0.6Co0.4)86Hf7B6Cu1 and (Fe0.7Co0.3)88Hf7B4Cu1 are thermally unstable at temperatures above 500°C.

Giant Magnetoimpedance of Cube/Feconi Electroplated Wires: Focus on Angular Sensoric

Giant magnetoimpedance effect (GMI) is a subject of special interest proved by applied electrodynamic and technological applications. GMI effect in ferromagnetic tubes is connected with the high sensitivity of the magnetic system to a circular magnetic field near the spin-reorientation magnetic phase transitions offering high sensitivity with respect to an external magnetic field. In this work the non-magnetic CuBe wires were covered by Fe20Co6Ni74 layers by electrodeposition. The thickness of 1 μm for magnetic layer was high enough in order to ensure the high GMI value. Longitudinal magnetic anisotropy was induced by post preparation annealing in a magnetic field of 160 A/m at 320℃ during 1 hour in order to obtain appropriate magnetisation process. Angular dependencies of GMI were measured in a frequency range of 1 to 10 MHz for driving currents of 2.5 to 20 mA. High longitudinal GMI of the order of 400% was observed at quite low frequency of 1 MHz. The highest value of the sensitivity of 520%/Oe was found for the active resistance: Linear sensitivities of 0.023 Ω/° and 0.05 Ω/° were observed for reasonably low fields of 240 and275 A/m respectively for small angles, where planar GMI elements are less effective.

Temperature dependent magnetization in Co-base nanowire arrays: Role of crystalline anisotropy

Co, Co(1−x)Pdx, and Co(1−y)Niy nanowire arrays have been prepared by electrochemical template-assisted growth. Hcp, fcc or both phases are detected in Co nanowires depending on their length (300 nm to 40 μm) and on the content of Pd (0 ≤ x ≤ 0.4) and Ni (0 ≤ y ≤ 0.8). Their magnetic behavior has been studied under longitudinal and perpendicular applied fields. The effective magnetic anisotropy is mostly determined by the balance between the shape and the crystalline terms, the latter depending on the fractional volume of hcp phase with strong perpendicular anisotropy and fcc phase with weaker longitudinal anisotropy. The temperature dependence of remanence and coercivity and the eventual observation of compensation temperature is interpreted as due to the different temperature dependence of shape and hcp crystalline anisotropy. Optimum longitudinal magnetic anisotropy is achieved in low Pd-content CoPd nanowires and in short Co nanowires.

Investigation of Magnetic Properties and Microstructure of Ultrathin Co Films Grown on Si(111)-7 × 7 Surface

Magnetic properties and growth mechanism of ultrathin Co films on Si(111)-7 x 7 surface have been studied by using both surface magneto-optic Kerr effect (SMOKE) and scanning tunneling microscopy (STM), respectively. STM results show that the growth mechanism of ultrathin Co films on Si(111)-7 x 7 surface at room temperature belongs to Stranski-Krastanov (SK) growth mode. Due to formation of CoSi2 layer, no magnetic signal could be detected by SMOKE for 1-4 ML Co deposited on Si(111) surface. Because of rougher surface, both longitudinal and perpendicular magnetic anisotropy configuration appear for 4.2-10 ML Co/Si(111) films. When the Co thickness is increased to 10 ML, only longitudinal anisotropy configuration is found, resulting from the contribution to the volume anisotropy. Furthermore, in-plane coercivity increases with Co coverage because of enhancement of ferromagnetic coupling with Co thickness, out-of-plane coercivity increases with Co coverage due to the increment of demagnetized field, induced by the rougher Co surface and pinhole structures.

Splitting of the Kondo resonance in anisotropic magnetic impurities on surfaces

Using the numerical renormalization group method, we study the splitting of the Kondo resonance by a magnetic field applied in different directions in the Kondo model for anisotropic magnetic impurities. Several types of magnetic anisotropy are considered: the XXZ exchange coupling anisotropy J⊥≠Jz, the longitudinal magnetic anisotropy DSz2 and the transverse magnetic anisotropy E(Sx2- Sy2). In the spin-1/2 model with the XXZ exchange coupling anisotropy, we find very small direction dependence in the magnitude of the splitting. In the spin-3/2 model with the easy-plane (D>0) anisotropy, we observe very unequal magnitudes with further differences between the x- and y-directions in the presence of an additional transverse anisotropy. A simple and rather intuitive interpretation is that the splitting is larger in magnetically soft directions. The magnitude of the splitting is directly related to the energy differences between spin states and it is only weakly modified by some multiplicative factor due to Kondo screening. The results for the S=3/2 model are in good agreement with recent scanning tunneling spectroscopy studies of Co impurities adsorbed on CuN islands on Cu(100) surfaces (Otte A F et al 2008 Nat. Phys. 4 847).