Hysteresis Loop Squareness Research Articles

Digital recording properties of thin metallic recording media

Earlier experimental works on the digital recording properties of thin metallic media are discussed in conjunction with available theoretical predictions. In particular, the roles of remanence and hysteresis loop squareness are examined, and some omissions and confusions in the earlier works are removed.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Noise and bit jitter performance of CoNiPt thin film longitudinal recording media and its effect on recording performance

The authors investigate the hysteretic properties and the recording behavior, such as bit jitter, overwrite, resolution, and on-track and off-track noise, of thin-film media based on a CoNiPt alloy. The films consisted of one alloy composition, sputtered under different process conditions to create films of different microstructure, magnetic hysteresis loop squareness, and coercivities. The factors that contribute to the bit shift are classified as originating from intersymbol interference, overwrite and media noise, on the basis of the results of magnetic recording characterization of the media. Analysis of the microstructure and hysteretic properties indicates that the noise is associated with the formation of magnetic clusters. >

Effect of polycrystalline sublayer films on the magnetic and structural properties of CoCr films

The magnetic and structural properties of Co-18 at. % Cr films were evaluated for high density longitudinal recording applications. The films exhibited in-plane magnetization, high coercivity (≲1000 Oe), and hysteresis loop squareness of 0.7–0.89 when the CoCr films were sputtered on sublayer films of Cr or Cr-20 at. % Co. The coercivity was correlated with the thicknesses of the CoCr film and the sublayer, the deposition conditions, and the percentage of CoCr grains with c-axis preferred orientation in the film plane.

Magnetic and dielectric properties of the spinel ferrite system Ni0.65Zn0.35Fe2−xMnxO4

The recent development of a high-magnetization nickel–zinc ferrite with stress-insensitive square hysteresis loop achieved through substitution of Mn3+ ions has prompted a study of the family Fe3+0.65Zn2+0.35 [Ni2+0.65Fe3+1.35−xMn3+x]O4. The magnetic and dielectric properties of compositions with x ranging from 0 to 0.4 were measured to determine the effects of the manganese substitutions over this concentration range. As anticipated, the saturation magnetizations decreased gradually with increasing x because of reduced magnetic moments in the B sublattice. Of greater importance, however, was the observation that maximum hysteresis loop squareness and minimum stress sensitivity occurred with x∼0.2. A single-ion magnetostriction model is used to interpret this result. Since the electrical resistivity remained above 106 Ω cm and the dielectric loss tangent stayed below 10−3 for the entire series, Fe2+ ion formation is probably negligible.

Magnetic properties of iron rich sputtered Fe-Al films

The magnetic properties of Fe-Al films with 6 to 15 at% Al made by sputtering from a hollow cathode ring segmented target have been studied as a function of Al concentration, substrate deposition temperature and oxygen concentration. The in the film plane intrinsic coercivities at room temperature range up to 100 Oe with a hysteresis loop squareness ratio, M r/ M s, of about 0.9. The easy axis of magnetization was in the film plane and fields 16 kOe were required to saturate certain samples perpendicular to the film plane.

Directly sputter synthesized high-energy product Sm-Co based ferromagnetic films

Different target configurations have been used to directly synthesize Sm-Co based films by selectively thermalized rf sputtering onto heated substrates in an in-plane magnetic field. Samples have been sputtered so that in certain cases a systematic gradient in Sm-to-Co concentration was created along the length of the substrates and in other cases so that films of a fixed uniform composition were deposited. Small subregions of a single substrate then serve as samples of a specific composition. For the Sm-to-Co composition range from 70 to 95 at. % Co gradient synthesized samples exhibit high magnetization and moderate intrinsic coercive forces. The maximum energy product of 20 MG Oe was obtained for a sample with 90.6 at. % Co containing mostly the Sm2Co17 phase. In addition, samples were synthesized from uniform composition targets at certain fixed compositions. Films sputtered from uniform composition Sm2(Co, Fe, Zr)17 targets exhibited square in-plane hysteresis loops and static energy products up to 21.2 MG Oe. It was observed that uniform composition SmCo5 films could be grown which exhibited either the (200) or the (110) texture as a function of the sputtering rate. Relatively higher sputtering rates of approximately 5 Å/sec resulted in the (200) texture growth pattern while lower rates resulted in (110) textured films. These differently textured SmCo5 films differ in both their microstructure and magnetic properties. The (110) textured film are finer in microstructure and magnetically harder than the (200) films. The uniform composition SmCo5 films of either texture in general were of smaller grain size and higher coercive forces than the SmCo5 subregions from films sputtered with a composition gradient spanning the 1–5 phase. A uniform composition SmCo5 film sputtered at 1.5 Å/sec which was (110) textured exhibited an intrinsic coercive force of 23 kOe and an energy product of 18 MG Oe at −63 °C. The high-energy products reported here are due to both the high induction and to the squareness of the in-plane hysteresis loops when measured in the direction parallel to the field applied during the sputter synthesis.

Magneto-optical recording on Tb-Fe based thin films

Amorphous Tb-Fe based thin films of Tb-Fe, TbGd-Fe and Tb-FeCo have been investigated for magneto-optical recording media. The films were deposited by using a two-source DC-sputtering method. The magnetic and magneto-optical properties of the films were investigated as a function of composition and it was found that the films with low rare-earth composition had perpendicular magnetization and showed a high squareness of hysteresis loop. In magneto-optical recording on the Tb-Fe based thin films deposited on plastic disks, a high carrier-to-noise ratio was obtained over a wide frequency range. The recording of FM video signal has been made possible on these high C/N disks.

Micromagnetics of domain walls in vertical recording

A detail micromagnetics calculation for a simplified model of domain walls in vertical recording is presented. From the resulting analytical expression for the wall magnetization distribution, wall energy density and wall width are determined for a single as well as for multiple walls. Whereas our simplified model presupposes a homogeneous medium, columnar structure is frequently observed in vertical recording media. Possible modifications to our results due to columnar formation is discussed. Finally, a comparison between the limiting recording densities of horizontal and vertical recording in the context of head field gradient and medium hysteresis loop squareness is given.

Preparation of High-Coercivity Co–Pt Alloy Films by Target-Facing Type of High-Rate Sputtering

Co1-xPtx (0≦x≦0.2) thin films were prepared by using a Target-Facing type of high-rate sputtering (TFTS). The films deposited at lower argon gas pressure PAr(≦5 mTorr) have only a low coercive force Hc (<700 Oe). However, the value of Hc for films deposited at higher PAr (≧10 mTorr) increases monotonically as the Pt content increases, and films with high Hc (>1 kOe) can be obtained at a Pt content of above 11 at%. These films, whose crystallites are oriented randomly, also have a large inplane uniaxial magnetic anistropy constant K1 (\\cong2.5×106 erg/cc) and excellent hysteresis loop squareness (S\\cong0.87, S*\\cong0.98).

A transition-metal–rare-earth alloy for perpendicular magnetic recording

Several Co-based media have been recognized to be convenient for perpendicular magnetic recording. These alloys present a good perpendicular magnetic anisotropy and high saturation magnetization, but high demagnetizing fields and a poor perpendicular hysteresis loop squareness σ⊥. This paper describes the conditions of deposition, magnetic properties, and recording tests results obtained with radio-frequence diode-sputtered FeTbGd thin films. Near to the compensation composition, the saturation magnetization and demagnetizing fields are low and σ⊥ is nearly 1. A SiO2 protective layer covered medium has been tested for magnetic recording with a conventional Winchester ferrite head. In these recording conditions, a density as high as 162 kiloflux changes per inch has been obtained. Such results show that transition-metal–rare-earth (TM-RE) alloys are suitable for perpendicular magnetic recording.

Permanent magnet properties of in-situ formed Cu–Fe multifilamentary compositesa)

Cu–Fe multifilamentary composites with up to 60 vol % Fe were prepared in situ. Magnetic hysteresis loops were obtained at room temperature as a function of composition, cross sectional area reduction, up to 99.9996%, and annealing conditions. Hci and (B⋅H)max increase with cross sectional area reduction and show pronounced changes on annealing. Hci=600, 520, and 380 Oe and Mr=5.6, 8.2, and 11.9 kG were measured in the smallest 30, 45, and 60 vol % Fe composites, respectively, following optimal heat treatment. (B⋅H)max=3.2 MG⋅Oe was measured in both Cu–45 vol % Fe and Cu–60 vol % Fe with hysteresis loop squareness of 0.95. Considering the excellent mechanical and transport properties, inexpensive constituent elements, and simple preparation, the in-situ formed Cu–Fe composites appear to have the potential for permanent magnet applications.

High coercivity Co and Co-Ni alloy films

A high coercivity and a high hysteresis loop squareness pure Co and Co-Ni (up to 50 at %) alloy films have been prepared by a new process. The new process involves the films, including N, being sputter deposited in an atmosphere of Ar-N2 mixture and annealed at temperature above 553 K. Most of the included N diffuses out from the film surface after annealing, and the films have a strong preferred orientation with the c axis parallel to the film plane. In Co70Ni30 alloy films, a high coercivity Hc of 1 kOe (80 kA/m) and a high hysteresis loop squareness S* of 0.95 are achieved. The values of Hc gradually decrease as the Ni/Co concentration ratio of the films departs from 30/70. There is a strong correlation between Hc and the preferred orientation of crystallites; Hc increases as the c axis orientation parallel to the film plane grows.

Life of Magnetic Electroless Co-P Thin Films

Effective life of electroless Co-P (2.5 wt%) thin films of about 100 nm in thickness was evaluated for both magnetic characteristics and corrosion. The Co-P films were grown on rigid Al substrates overcoated with nonmagnetic Ni-P thick films and were finally covered with electroplated Rh thin films of 120 nm - 180 nm in thickness. The life of the magnetic characteristics was defined as the time to reach 10% deviation from the initial values of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> (coercive force), B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> (remanence), and S (squareness of hysteresis loop). The life of the films for corrosion was defined as the induction period of corrosion. An increase of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> was observed above 80°C for isothermal annealing, but B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> and S were unchanged. The activation energy of the variation of H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> was approximately 0.7 eV below 144°C. The life of magnetic characteristics was estimated to be approximately 4.1 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> - 2.3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> hrs at 55°C corresponding to the allowable maximum temperature in field service. The life for corrosion was influenced by the quality of Rh films.

An investigation of amorphous Tb-Fe thin films for magneto-optic memory application

Amorphous Tb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.16 &lt; x &lt; 0.35</tex> ) thin films produced by rf co-sputtering have been investigated for magneto-optic memory media application. The anisotropy, hysteresis and coercivity of the films were investigated as a function of composition and film thickness. The sputtered films were overcoated with thermally evaporated SiO. The effect of SiO thickness on the Kerr magneto-optic enhancement and the reflectivity was also measured. It was found that the magnetization and coercivity of those films having perpendicular anisotropy change dramatically not only with target composition but also with film thickness. Thin films having a high hysteresis loop squareness and a coercivity appropriate for magneto-optic recording (500 to 2000 Oe.) were produced from film compositions near the compensation composition of 22.3 at. % Tb. Thermomagnetic writing and reading of the TbFe films were made with a GaAs laser. The results show that the films have a high writing sensitivity (threshold energy of 0.2 nJ and saturation energy of 0.3 nJ) and a high reading contrast for bit sizes of 1 micron.

High coercivity and high hysteresis loop squareness of sputtered Co-Re thin film

High coercivity and high hysteresis loop squareness of sputtered Co-Re thin film

The physical limits of high density recording in metallic magnetic thin film media

The fundamental physical limits of high density, saturation recording in high hysteresis loop squareness magnetic isotropic metallic media have been investigated based on observations of micromagnetic structure of recorded Co-Re thin films. Study based on the configuration of the "feather-like" ripple structures of the Lorentz TEM image at the transition region and electron deflection shadow image of the surface field configuration of the recorded media indicate that the physical limit of high density recording in the metallic media is the size of magnetic clusters existing in the film. For a Co-10 at % Re film with H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> between 200 to 500 oe., thickness of about 50 nm and S* > 90%, the maximum linear packing density the film can provide, as determined from the cluster size, would be less than 25,000 FRPI.

High coercivity and high hysteresis loop squareness of sputtered Co-Re thin film

The coercivity, hysteresis loop squareness, and microstructure of the sputtered Co and Co-rich Co-Re alloy thin films are presented. Correlations between the microstructures and the magnetic properties are established. It was found that the sputtered Co films have a mixture of fcc and hcp phases, making it impossible to obtain sputtered Co films possessing both high Hc and high M-H loop squareness. For Co-Re alloy films however, it was possible to obtain films with a pure hcp phase below substrate temperatures of 300 °C. By controlling the microstructure of the Co-Re films through variation of the sputtering variables, films having Hc’s up to 700 Oe and squareness ratios (Mr/Ms and S*) of more than 80% were obtained. The micromagnetic structures of these Co-Re films were also investigated using Lorentz microscopy and the results are discussed in terms of the microstructure and magnetocrystalline anisotropy of the film.

Abstract: High coercivity and high hysteresis loop squareness of sputtered Co-Re thin film

The correlation between the magnetic properties and microstructures of sputtered pure Co and Co-Re alloy thin films have been investigated. Magnetic properties were investigated via hysteresis loop measurements while microstructure was determined using TEM. (AIP)

The influence of coherent domain size and the perfection of the 〈1010〉 texture on the magnetic properties of electroplated cobalt

Cobalt layers with texture 〈1010〉 have been electrodeposited on copper substrates. The block size along the direction parallel to the substrate has been determined by means of transmission electron micrographs and normal to the substrate by X-ray line-width analysis. It is found that overpotential increase in galvanostatic conditions leads to a decrease of both the block size and perfection of the 〈1010〉 texture. The reduction of texture perfection affects the hysteresis loop squareness ratio. The coercive force decreases as result of structure dispersity increase and it is found to be in inverse ratio of the coherent domain size. The possible relation among the elements mentioned above of the structure and magnetic properties is discussed. [Russian Text Ignored].

Magnetic properties of cobalt rare-earth thin films

This paper describes the magnetic properties of dc sputtered thin films of Co-Gd and Co-Sm in various compositions. Magnetic moment density, hysteresis loop coercivity and squareness, and rotational hysteresis loss measurements are reported. Crystallite and domain sizes were observed with an electron microscope for a few compositions. A tentative model of magnetization reversal is proposed for some of the compositions.