Distinctive characteristics of barium ferrite media

In this paper we introduce barium ferrite tape samples with a high recording characteristic in the conventional longitudinal magnetization mode, and explain the origin of their high output voltage at high recording densities, with reference to the effect of the magnetic characteristic and the behavior of remanent magnetization. Longitudinally and non-oriented barium ferrite recording media were prepared using the same magnetic paint based on a single barium ferrite magnetic particle. The barium ferrite tapes thus prepared were inferior to ultra-high density metal tapes with regard to surface roughness and magnetic energy, but exhibit better recording characteristics at high recording densities above 80 kFRPI or so. In particular, the origin of the high recording characteristic of longitudinally oriented barium-ferrite tape samples may be explained by the effect of the sample remanence curves, rather than by perpendicular magnetization.

Key factor for low anisotropy and high irreversibility field in (Cu,C)Ba2Ca3Cu4O11+δ

The feasibility of a high-density magnetic particulate recording medium with a thin magnetic layer of evenly dispersed high-coercivity barium-ferrite particles was investigated. Thermal stability, writability, and an areal recording density of 17.5 Gb/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> were confirmed for a flexible disk system using a giant magnetoresistive head

Microstructure and magnetic properties of grain boundary diffused Nd-Fe-B magnets with Tb-Al-Ga alloy

We investigated how a Ru underlayer contributed to the in-plane magnetic anisotropy of an FeCoB upper layer. The Ru underlayer with a higher degree of Ru (001) orientation induced higher in-plane magnetic anisotropy in the FeCoB upper layer. A Si/NiFe seed layer, which was located beneath the Ru underlayer, changed the Ru crystalline orientation from random to (001) preferential orientation and induced a remarkably high in-plane anisotropy field of 540 Oe. The in-plane anisotropy of Ru crystallites in the Ru underlayer is discussed in the paper. The Ru (002) pole_figure indicated isotropic in-plane alignment of Ru crystallites. Si/NiFe/Ru/FeCoB film was prepared using two methods, i.e., with unturned and turned underlayer deposition. The direction of anisotropic alignment of FeCo crystallites and in-plane magnetic anisotropy of the FeCoB layer was not influenced by the direction of the Ru underlayer; therefore, the Ru underlayer was not a dominant factor, and the oblique incidence effect caused by the configuration of Facing Targets Sputtering system (FTS) was a dominant factor that induced in-plane magnetic anisotropy in the FeCoB layer. The Ru underlayer may have contributed to an increment of the oblique incidence effect.

Results of temperature- and magnetic field-dependent strain measurements across the first-order antiferromagnetic to ferromagnetic phase transition in Fe0.955Ni0.045Rh are presented. Distinct thermal and magnetic field hystereses are observed in the measured strain across the phase transition. The minor hysteresis loops inside the hysteretic regime across the temperature-driven transition are modeled using the Preisach model of hysteresis. The applicability of the Preisach model to explain the general features of minor hysteresis loops is discussed for a disorder influenced first-order transition. The minor hysteresis loops show the property of retaining the memory of the starting or end point of the temperature cycle followed within the hysteretic region. A larger temperature excursion within the hysteretic region wipes out the memory of a smaller temperature cycle which contains one of the extrema of the larger cycle. The end-point memory and the wiping-out property of the minor hysteresis loops can be described quite well within the Preisach model, irrespective of the temperature history followed to reach a particular starting point. Thermo-magnetic history effects across the magnetic field-induced transition are explained, which will enable the choice of the starting point of an experimental cycle in the field–temperature phase space so as to achieve the desired functionality. Our results highlight the necessity to understand the influence of disorder on a first-order phase transition so as to achieve a repeatable performance of materials whose functionalities are based on such a transition.

We have investigated effects of long-term thermal aging at 550°C up to 10000 h on major-loop coercivity, hysteresis scaling of minor loops, and first-order reversal curves (FORCs) for low-alloy pressure vessel steels with low and high Ni contents. While major-loop coercivity and minor-loop coefficient of the scaling exhibit a gradual decrease with aging for high-Ni steel, those for low-Ni one are very weakly dependent on aging time. On the other hand, we found that FORC distribution becomes steep along both axes of interaction and switching fields and the peak shifts toward a lower switching field for both steels. Considering that there is no significant development of nanoscale precipitates during the aging as revealed with small-angle neutron scattering experiments, a relaxation of lattice strain in a matrix, possibly associated with diffusion of Ni atoms, may dominate magnetic properties at 550°C.

A sputtered FePt(BN, Re, C) film, here boron nitride (BN), was compared to a reference sample FePt(BN, Ag, C). Intrinsically, these films illustrate a high anisotropy field (Hk) and perpendicular magnetocrystalline anisotropy (Ku),although the reference sample shows a higher value (Hk = 69.5 kOe, Ku = 1.74 × 107 erg/cm3) than the FePt(BN, Re, C) film (Hk = 66.9 kOe, Ku = 1.46 × 107 erg/cm3). However, the small difference in the anisotropy constant (K2/K1) ratio presents a close tendency in the angular dependence of the switching field. Extrinsically, the out-of-plane coercivity for the reference sample is 32 kOe, which is also higher than the FePt(BN, Re, C) film (Hc = 27 kOe), and both films present lower remanence (Mr(parallel)/Mr(perpendicular) = 0.08~0.12), that is, the index for perpendicular magnetic anisotropy. The higher perpendicular magnetization for both films was due to highly (001) textured FePt films, which was also evidenced by the tight rocking width of 4.1°/3.0° for (001)/(002) X-ray diffraction peaks, respectively, and high-enough ordering degree. The reference sample was measured to have a higher ordering degree (S = 0.84) than FePt(BN, Re, C) (S = 0.63). As a result, the Ag segregant shows stronger ability to promote the ordering of the FePt film; however, the FePt(BN, Re, C) film still has comparable magnetic properties without Ag doping. From the surface and elemental composition analysis, the metallic Re atoms found in the FePt lattice result in a strong spin–orbital coupling between transition metal Fe (3d electron) and heavy metals (Re, Pt) (5d electron) and we conducted high magnetocrystalline anisotropy (Ku). Above is the explanation that the lower-ordered FePt(BN, Re, C) film still has high-enough Ku and out-of-plane Hc. Regarding the microstructure, both the reference sample and FePt(BN, Re, C) show granular structure and columnar grains, and the respective average grain size and distributions are 6.60 nm (12.5%) and 11.2 nm (15.9%). The average widths of the grain boundaries and the aspect ratio of the columnar grain height are 2.05 nm, 1.00 nm, 2.35 nm, and 1.70 nm, respectively.

A CoPtCr-SiO2 film is a potential material for high-density perpendicular recording media due to their high magnetic anisotropy constant Ku. However, the value of Ku decreases in high levels of Pt content. In this study, this phenomenon was analyzed by synchrotron radiation grazing incidence x-ray diffraction and transmission electron microscopy techniques. Although the CoPtCr-SiO2 films contained almost no fcc phase at 20at.% Pt or less, it increased remarkably at 30at.% Pt. This result coincided with the variations of Ku with respect to the Pt content for the CoPtCr-SiO2 films. We consider that the fcc phase formation at Pt content levels in the vicinity of 30at.% is an influential factor of the Ku reduction. Our techniques proved to be sensitive for the detection of fcc regions in the CoPtCr-SiO2 films.

The shape of minor loops has been measured as a function of remanence for Co-coated gamma -Fe/sub 2/O/sub 3/, barium ferrite, and iron particulate media, as well as a series of particle assemblies in which particle orientation and spacing were varied. The width of the loops at zero field and their axial slope were used as quantitative measures of their shape. In all cases, the minor loops for the same field extrema but different values of average remanence are not congruent. According to an operator analysis of the Preisach model by I.D. Mayergoyz (1986), noncongruence indicates that the Preisach distribution is also a function of field history. This result is in agreement with other experimental investigations of this issue. Hence, noncongruence provides a confirmation of the analysis by Mayergoyz. The amount of noncongruence is used here to determine the degree to which the Preisach distributions for various types of particle assemblies depend on field history.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The origin of high uniaxial magnetic asnisotropy in FeCoB thin films was investigated by focusing on the changes in FeCo crystal distortion and alignment. The films were prepared by facing targets sputtering using F <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">88.8</sub> Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">27.2</sub> B <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> alloy targets and examined with X-ray diffraction (XRD) analysis. Preparation of a Ru underlayer showed reduction of coercivity H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> from 130 to 14 Oe and developed remarkably high-anisotropy field H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> , of 500 Oe. FeCo(110) of the FeCoB film with a Ru underlayer revealed an oblique crystal growth and a preferred orientation in the film plane that possessed (110) [110] along the easy axis. FeCo(110) lattice spacing has 0.5% expansion along the easy axis, which induces that the magnetoelastic energy -E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">elastic</sub> of 3.8 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> erg/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> exists along the easy axis due to an inverse magnetostriction effect. The estimated H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> from the E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">elastic</sub> was 470 Oe, which corresponded well with the measured H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> of 500 Oe. This indicates that the strain in FeCo lattice is the origin of the remarkably high magnetic anisotropy.

The recording physics of bit patterned media is studied for areal densities of around 2 Tbits/inch2, focused on number of grains per bit. Write error rate and signal to noise ratio in a function of number of grains are derived as analytical functions based on the statistics theory on the binomial distribution. Modeling of writing process based on the head field gradient and switching field distribution and interference fields, is presented to extract the write-head and media parameters which are necessary to attain a high areal density recording.

We studied the effects of metal/MgO seeds (metal = Ta, Ru, or Pd) on the crystalline structure and perpendicular magnetic properties of Co/Pd multilayers to investigate the possibility of developing a (100) texture with sufficiently high perpendicular anisotropy and small switching field distributions for applications such as patterned media and perpendicular magnetic random access memories. The Pd/MgO or the MgO seed successfully promoted a (100) texture of Co/Pd multilayers. In particular, the Pd/MgO seed developed a strong (100) texture in the Co/Pd multilayer and resulted in perpendicular magnetic anisotropies ∼2 × 106 erg/cm3. On the other hand, the Co/Pd multilayer with the Ta/MgO or the Ru/MgO seed showed a strong (111) texture, inducing a perpendicular magnetic anisotropy higher than that of the (100) textured films. The coercive fields of Co/Pd multilayers with the (111) texture were over 4 kOe and higher than those with the (100) texture, which were ∼2 kOe when they were patterned into 2 × 2 μm2 islands. The switching field distributions of the Co/Pd multilayers with the (100) texture were smaller than those of the Co/Pd multilayers with the (111) texture. Our findings suggest that the Pd/MgO or the MgO seed can be a template suitable for device applications.

We explore the response of a magnetic bilayer to a driving microwave field using micromagnetic simulations. The bilayer consists of 8 nm of a material with a high uniaxial anisotropy and 56 nm of a material with a lower uniaxial anisotropy. The width and length of the structure is 100 × 100 square microns. A small applied field, opposite to the magnetization, switches most of the lower anisotropy material but not the higher anisotropy material, forming a domain wall between the two materials. We evaluate the frequencies of the magnetic eigenmodes for the entire system using Fourier analysis and then drive the structure with an oscillating magnetic field at each of the eigenfrequencies. When the oscillating microwave field is added, the static switching field required to align both layers is decreased compared to the undriven case. With a driving field strength of 120 Oe the switching field is reduced by about 40%, from 1.12 kOe for the undriven case to 0.55 Oe for the driven case.

Incoherent magnetization reversal in Co–Pt nanodots investigated by magnetic force microscopy