Hard Magnetic Films Research Articles

Magnetic and microstructural properties of hard magnetic NdFeB films prepared on a Ta buffer by pulsed laser deposition

Hard magnetic NdFeB films were prepared by pulsed laser deposition at different substrate temperatures on a Ta buffer. With increasing deposition temperature, the in-plane to out-of-plane remanence ratio decreases to less than 0.1, indicating a very good perpendicular magnetic anisotropy. However, for temperatures above 600/spl deg/C the increasing grain size reduces coercivity. A reduction in film thickness reduces grain size and increases the coercivity up to 1.5 T while maintaining a good magnetic texture.

Effect of rare earth content on microstructure and magnetic properties of SmCo and NdFeB thin films

Thin films of highly anisotropic rare earth intermetallic compounds increasingly come into the focus of interest for application in magnetic miniature devices. We prepared hard magnetic SmCo and NdFeB films by pulsed laser deposition and investigated the influence of rare-earth content on phase formation, microstructure, and magnetic properties. The phase evolution with rare earth content, as observed by x-ray diffraction, shows a distinct difference for the two systems. For SmCo a disordered SmCo7 structure is found at low Sm content and a change in the lattice constants is observed for a Sm-rich sample. Simultaneously, the coercive field improves whereas the magnetic in-plane texture found for Sm-poor films vanishes for higher Sm content. For NdFeB the increase in Nd content leads to an additional Nd phase because of the small homogeneity range. Contrary to the bulk, coercivity is reduced, which can be attributed to a significant increase of grain size and roughness.

Fabrication and magnetic properties of Nd 11.4La 0.6Fe 76M 2B 10 (M=Ti, Cr) films

Hard magnetic films Nd 11.4La 0.6Fe 76M 2B 10 (M=Ti and Cr) were fabricated by DC sputtering to explore the possible applications in micro-electrical mechanical systems. X-ray diffraction data indicate that the Ti-containing sample consists of R 2Fe 14B and minor phases of Fe 3B and R 2Fe 23B 3. For the Cr-containing sample, only R 2Fe 14B and Fe 3B phases were observed. The Nd 11.4La 0.6Fe 76Ti 2B 10 film exhibits better magnetic properties of B r=7.0 kG, i H c=11.5 kOe, and ( BH) max=11.0 MG Oe. The smaller amount of soft magnetic Fe 3B phase and the refined microstructure may account for the improved magnetic properties. Optimum process parameters are strongly dependent on the chemical compositions of the films, including post-annealing, working pressure of Ar, and thickness of the film, etc.

The dual spin valve head for high density recording

A dual spin valve head with synthetic antiferromagnetic pinned layers, DSSV, consists of a reader and a writer. The key fundamental concept of the magnetic materials for the reader and the writer of the DSSV will be discussed in this paper. The reader consists of a sensor stripe, a pair of hard magnetic bias films for the purpose of stabilization, and a pair of current leads. The reader has a high sensor sensitivity because it allows a longer coherent spin dependent electron mean free path that enhances the giant magnetoresistance change. The sensor is a symmetrical multilayer film structure that was optimized to have a high GMR ratio. The writer is a conventional inductive head with high magnetic moment poles consisting a thin layer of laminated high moment FeRhN film material The multilayer film sturcture of the DSSV sensor, its magnetic properties, and the head performance will be discussed in detail. The possible future development will also be discussed.

Magnetically actuated micromirror and measurement system for motion characteristics using specular reflection

Micromachined magnetically actuated torsional micromirrors have been fabricated. The micromirrors based on silicon were actuated by moving magnet system using hard magnetic (Co-Pt) or soft magnetic (Fe-Ni) thin films. And a system to measure motion characteristics of the micromirrors was assembled with an optical table, optical mounts, and optics. The system is based on a specular reflection of He-Ne laser from the micromirrors. We measured static and resonance characteristics of the micromirrors with Co-Pt film or Fe-Ni film. Then we measured Q factors of the micromirrors; with Co-Pt film in vacuum. Using our system for measurements, we obtained motion characteristics of micromirrors at large angular deflections. Measured resonance characteristics of all micromirrors are in good agreement with the equation of forced vibration with viscous damping. Micromirrors with Co-Pt films have better reproducibility of torsional motions than ones with Fe-Ni films in both dc magnetic field and ac magnetic field. And micromirrors with Fe-Ni films have torsional motion with subpeak at resonance characteristics. The Co-Pt film is more useful as a magnetic film for the micromirror than the Fe-Ni film at static and resonance characteristics.

Effect of Cr and Ta buffers on hard magnetic Nd 2Fe 14B films

Phase formation, microstructure and interdiffusion of hard magnetic Nd 2Fe 14B films on Cr and Ta buffers are compared, and the consequences of the chosen buffer on the magnetic properties of the films are considered. While on a Ta buffer, the growth is more perfect than on Cr and a higher coercivity is found in films on Cr, indicating the importance of domain wall pinning.

Hard magnetic SmCo thin films prepared by pulsed laser deposition

Hard magnetic SmCo films were prepared by pulsed laser deposition in UHV and at moderate background pressures on polycrystalline Al 2O 3. Structure and magnetic properties are discussed for varying Sm-content. The perpendicular anisotropy observed at a deposition pressure of 0.06 mbar is compared with texturing models known for sputtered samples.

Collimated deposition of hard bias magnetic films via long-throw techniques

We present an optimization of long-throw sputter-deposited Cr/CoCrPt films, specifically for (lifted-off) hard bias applications in an AMR/GMR head. Deposition was carried out in the target-to-substrate (T/S) range of 7–9 in., with pressure down to 0.25 mTorr. On increasing the T/S by 1 in., a 5% reduction in coercivity was observed, and shown to be only partially explained by the deposition rate reduction. On the other hand, lower gas pressure during the CoCrPt deposition significantly increased the coercivity. Higher target power and higher substrate bias also increased the coercivity. All the observed T/S, pressure, target power, and bias dependencies suggest enhanced coercivity is associated with higher CoCrPt adatom mobility. X-ray diffraction data showed the relative intensity of the (0002) to the (1010) peak to be decreased both with higher CoCrPt deposition power or substrate bias; more in-plane c-axis texture could explain the increased coercivity. A sputter etch of the wafer before Cr deposition increased the coercivity by about 300 Oe. A combination of these techniques may be used to compensate for the deterioration in magnetic properties due to the long-throw. Optimal properties of 1790 Oe coercivity and 3.5 memu/cm2 Mrt were achieved.

Observations of exchange coupling in Nd 2Fe 14B/Fe/Nd 2Fe 14B sandwich structures and their magnetic properties

Sandwich structures of Nd 2Fe 14B/Fe/Nd 2Fe 14B magnetic films have been grown by a KrF excimer laser ( λ=248 nm) ablation technique. Magnetic properties were characterized by varying the thickness of hard (Nd 2Fe 14B) and soft (Fe) magnetic films and the volume fraction as well. In the ( x) nm [NdFeB]/( y) nm [Fe]/( x) nm [NdFeB]/(1 0 0)Si structure the thickness ( x) was varied from 3.6 to 54 nm, and ( y) from 15 to 112 nm. At ( y)=15–20 nm where the volume fraction of Fe corresponded to 61–75%, the sandwich structure exhibited an enhanced M r/ M s and i H c as well from the result of the exchange coupling between the magnetic layers. Experimentally calculated exchange constant ( A s) of A s=2.5×10 −10 J/m was estimated using the intrinsic coercivity ( i H c ) of 1.2 kOe at 5 K for the sandwich magnetic trilayers.

Correlation of magnetoresistive sensitivity mapping (MSM) with spin stand performance

Magnetoresistive sensitivity mapping (MSM) uses an AFM tip coated with a hard magnetic film as a flux source to provide a read sensitivity profile on a biased MR head. The resulting MSM signal is monitored using a modified electronics package attached to a standard probe microscope. MSM scans are compared with standard trackscans and /spl mu/-tracks of the same heads and are shown to detect the same anomalies in the read sensitivity profile.

Ultrahigh coercive force in epitaxial Fe-Pt(0 0 1) films

Perpendicular magnetized epitaxial Fe-Pt(0 0 1) thin films with the CuAuI-type structure were prepared by an electron beam evaporation method. The films of about 120–250 Å thickness exhibit an ultrahigh coercive force of about 48 kOe at room temperature. These hard magnetic films are mainly composed of fine particles of about 0.1 μm in diameter.

Vertical AMR sensor with new magnetic stabilizing design

We have developed a new vertical anisotropic magnetoresistive (AMR) sensor for narrow track recording. In this design, the lower NiFe layer is deposited on the hard magnetic film. A large exchange coupling occurs between these films. The upper NiFe layer is magnetostatically coupled with the lower NiFe film. As a result, a stable operation is achieved even with a narrow 1 /spl mu/m track width sensor. This head exhibits excellent recording characteristics.

Bicrystal structure CoPt biasing films on ultrathin Cr seed layers for spin-valve GMR head

We have successfully obtained the CoPt hard magnetic thin films of Hc=2200Oe, S=0.94, and Mr=800emu/cc on ultrathin Cr seed layers for domain control of spin-valve GMR heads. This good performance is considered to be due to the bicrystal structure of CoPt films. The microstructure was strongly dependent on the surface treatment before the Cr seed layer deposition. We believe that the mixing amorphous layer due to the strong binding between Cr and AlOx, resulting in large grain size of Cr with (200) orientation, is responsible for realizing the bicrystal structure.

Micromagnetic Modeling: Theory and Applications in Magnetic Thin Films

Micromagnetic theory concerns detailed magnetization configurations and the magnetization-reversal processes in a ferromagnetic system. By combining the original micromagnetic theory with a dynamic description of magnetization orientations, one can simulate complete magnetization processes and calculate important properties such as magnetic hysteresis and magnetic switching dynamics. Not only can micromagnetic simulation predict complex magnetic-domain configurations in a ferromagnetic system, it also can generate transient pictures showing how a complex domain configuration forms. Very important among these systems are ferromagnetic thin films, particularly those used in sensors and recording devices. Micromagnetic modeling not only has enriched our understanding of existing magnetic films but has also been used to successfully predict the magnetic properties of new film microstructures created for particular applications.In this article, a brief introduction of micromagnetic-modeling theory will be given. Modeling of soft and hard magnetic films will be discussed separately through two examples illustrating the essence of micromagnetic-magnetization processes in these films.

Barberpole type MR head stabilized by hard magnetic films

Composite magnetic thin film heads were developed for DCC systems, which incorporate digital read/write elements and analog read elements on one head chip. In DCC heads, suppression of Barkhausen noise (BHN) and instability in reproduce characteristics is particularly important. In order to solve these problems, a new barberpole structure incorporating a new arrangement of hard magnet films on the MR films was adopted.

Fabrication of small flying machines using magnetic thin films

A small flying machine based upon a new mechanism was realized. The flying machine driven by magnetic torque had hard magnetic films as wings and a soft magnetic wire as a body, respectively. The wing has two hinges, which create different drag during up and down strokes, and produced lifting force. Shape magnetic anisotropy of the body stabilized the attitude. The flying machine flew without power supply cables and guides when an alternating magnetic field of more than 400 Oe around 12 Hz was applied.

Stability and biasing characteristics of a permanent magnet biased SAL/MR device

A longitudinal bias field can be produced by exchange-coupling a soft ferromagnetic MR layer, such as NiFe with a permanent magnetic (PM) thin film. This exchange bias field creates a single domain state in the MR layer and thereby suppresses the Barkhausen noise. The center active region of an MR sensor could remain magnetically soft if only the end regions of the MR stripe are exchange coupled. A CoNiCr hard magnetic thin film is deposited on top of a Cr underlayer to achieve a high coercivity of 750 Oe. The exchange coupling effect between the CoNiCr and the NiFe is significantly enhanced after a 290/spl deg/C 3-hour annealing cycle. Unshielded devices fabricated with the patterned hard bias scheme were found very stable and the biasing characteristics are quite different from those coupled with FeMn. The PM materials are generally less prone to corrosion as compared to FeMn and are more compatible with wafer and slider fabrication processes. >

Magnetization processes in CoNiW films

The torque curves of hard magnetic CoNiW films with perpendicular magnetic anisotropy are analysed. Using the dependence of the rotational hysteresis energy losses on the field, both in the film plane and perpendicular to it, a conclusion is drawn about the magnetic structure of the films and the mechanism of magnetization reversal consisting of an inhomogeneous rotation of the magnetization vector.

On magnetization reversal in hard magnetic Co-W films

The angular dependences of the coercivity, hysteresis losses as well as rotational hysteresis losses have been investigated to determine the mechanism of magnetization reversal in electrodeposited Co-W films both with perpendicular and in-plane anisotropy. It is shown that the films with columnar structure and the [001] texture reverse preferably by incoherent rotational processes. The appearance of columnar crystallites with the [100] orientation as well as the existence of the initial layer promote the domain-wall motion processes.

Apparatus for measuring the hysteresis loop of hard magnetic films on large magnetic recording disk

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