Hysteresis Loop Squareness Research Articles

On the temperature stability of the cube texture in 50-50 Ni-Fe tape

Hysteresis loop squareness in 50Ni-50Fe alloys is shown to be well related to the sharpness of the cube texture. The development and the temperature stability of the cube texture (to prevent secondary recrystallization) is therefore of great interest for industrial applications. The aim of this investigation was to determine to what extent this temperature stability can be controlled by industrial process: cold-rolling reduction and 2 nd phase particules content. A critical radius for a thermally activated nucleation of secondary recrystallization was introduced to discuss experimental results.

Structure and magnetic properties of BaCoTiFe10O19 thin films with an easy-axis in-plane orientation

BaCoTiFe10O19 hexaferrite thin films with an easy-axis in-plane orientation were prepared by crystallization of amorphous films deposited by rf magnetron sputtering. The structure and magnetic properties were investigated. It is shown that CoTi-doping leads to a reduction of spontaneous magnetization and magnetic moment, which is caused by non-collinear magnetic structure and surface spin canting of small particles. The substitution of CoTi for Fe can adjust coercivity and Curie temperature over a very wide range, while still maintaining the room temperature magnetization. It is found that BaCoTiFe10O19 films exhibit a large squareness of hysteresis loop, Sq = 0.68. Thus, this film is desirable for high-density longitudinal recording systems.

The role of NiAl underlayers in longitudinal thin-film recording media

Longitudinal recording media made with chromium and with nickel-aluminum underlayers are compared. NiAl films have smaller grains and random crystallographic orientation, while Cr films have larger grains and either a {110} or a {200} preferred orientation depending on the deposition conditions. Cobalt alloy films grown on NiAl have nearly random crystallographic orientation and significant c-axis out-of-plane component, and lower hysteresis loop squareness and coercivity than films made on a heated Cr underlayer. NiAl-underlayer media do not exhibit in-plane magnetic anisotropy induced by the substrate texture lines. CoCrTaPt/Cr/NiAl media had higher overwrite than CoCrTaPt/Cr media due to higher coercive squareness and a sharper hysteresis loop closure.

Properties of ferrites at low temperatures (invited)

At cryogenic temperatures magnetic properties of ferrites change significantly from their values at room temperature, which has been the main regime for most device applications. Recently, microwave ferrite devices with superconducting microstrip circuits have been demonstrated at a temperature of 77 K with virtually no electrical conduction losses. Conventional ferrimagnetic garnet and spinel compositions, however, are not generally optimized for low temperatures and may require chemical redesign if the full potential of these devices is to be realized. Saturation magnetizations increase according to the Brillouin–Weiss function dependence that is characteristic of all ferromagnetic materials. Increased magnetocrystalline anisotropy and magnetostriction can have large effects on hysteresis loop squareness and coercive fields that are essential for stable phase shift and efficient switching. Rare-earth impurities and other ions with short spin-lattice relaxation times can cause increased microwave losses. In this article, the basic magnetochemistry pertaining to ferrites will be examined for adaptation of ferrite technology to cryogenic environments.

Co/Pt Disks with a Simplified Structure

Potentially low cost Co/Pt multilayer disks were fabricated using a simplified disk structure. Ultrathin seed layers of dielectrics were used to enhance the coercivity and squareness of the Kerr hysteresis loop. Both Co/Pt superlattices and the dielectrics were deposited under low vacuum. The total cycle time consisting of loading the PC substrate into the vacuum chamber, pumping the sputtering chamber to a base pressure, and deposition of the ITO seed layer and the Co/Pt multilayer was reduced to less than ten seconds. Cyclability and recording performance of the conventional media is retained.

Study of magnetic reorientation phenomenon and magnetic properties of Pd/(Pt/Co/Pt) multilayers

Pd/(Pt/Co/Pt) modulated multilayer films have been prepared at substrate temperatures ranging from room temperature to 350 °C by e-beam evaporation using various buffer layers. All these films exhibit perpendicular magnetic anisotropy with square polar Kerr hysteresis loops at room temperature. However, we observed a magnetic reorientation from a perpendicular anisotropy to an in-plane anisotropy at temperatures close to the Curie temperature TC. The reorientation temperature TR is found to depend strongly on the nonmagnetic Pd-spacer thickness in these Pd/(Pt/Co/Pt) multilayers. Over the room temperature to TR range, we observe a linear temperature dependence of magnetic coercivity. AFM and STM characterization of the role of buffer layers on the microstructure, the dependence of coercivity and squareness of the Kerr hysteresis loops on the buffer layers of Au, Pt, and Al are also presented.

PLZT-based multilayer composite thin films, part I: Experimental investigation of composite film structures

Composite thin films produced by depositing alternating layers of various PLZT compositions were fabricated on Pt-coated Si wafer and Ag foil substrates. Films were prepared by MOD processes including automatic spin and dip coating from acetate precursors followed by annealing at 700°C. Ferroelectric (FE)/antiferroelectric (AFE), FE/relaxor and relaxor/AFE composites consisted of individual layer compositions including ferroelectric PLZT 2/55/45 and 7/65/35; AFE PLZT 0/100/0, 0/96/4 and 0/95/5; relaxor PLZT 9.5/65/35 and 12/65/35. The structural and electrical properties of the composite films were investigated. Composites were developed with 1) improved AFE-to-FE domain switching with decreased AFE-to-FE transition field and increased saturation polarization for materials with AFE-type properties, 2) increased induced polarization with decreased coercivity and polarization remanence for relaxor-type composites and 3) increased hysteresis loop squareness for ferroelectric memory materials compared with fi...

Magnetic and magneto-optical properties of CoPtM (M = Re, Ru) alloy films for a new magneto-optical recording material

CoPtM (M = Re, Ru) ternary alloy films have been investigated as new magneto-optical materials for blue laser recording. The CoPtRe and CoPtRu alloy films were prepared by sputtering without a heating process, and exhibited good perpendicular magnetic anisotropy and magnetic hysteresis loop squareness. For the magneto-optical properties, the figure of merit for the CoPtRe alloy film with less than 15 at% Re at λ < 530nm is shown to be superior to that for TbFeCo amorphous film and inferior 0–4 dB to that of Co/Pt multilayers.

Behaviors of Ga during crystallization of amorphous Nd 4.5Fe 73Ga 1Co 3B 18.5 by fluorescence XAFS

Combined addition of Ga and Co into Fe 3B-based NdFeB hard magnetic materials improves squareness of hysteresis loop and remanence. Since Ga addition is believed to reduce the grain size of the crystallites precipitated from the as-quenched amorphous state, fluorescence XAFS measurements of the Ga K-edge are carried out. A small change of XAFS spectrum for the as-quenched (amorphous) state just after the Fe 3B precipitation suggests that Ga is excluded from Fe 3B crystallites to surrounding amorphous region. Good agreement of the observed XAFS spectra for the annealed at a higher temperature where Nd 2Fe 14B is precipitated with the calculated CsCl-type CoGa alloy indicates a preferential bonding between Ga and Co.

Improved determination of the ultrathin structural parameters of Co/Pd multilayered film, and its magnetic and magneto‐optical properties

Co/Pd multilayered films with ultrathin layers of Co were prepared by alternating deposition in an ultrahigh‐vacuum physical‐vapor‐deposition system. The individual layer thicknesses of the samples were estimated making use of the angular positions of x‐ray diffraction peaks. The magnetic and magneto‐optical properties were found to vary depending on Pd buffer layer and Pd sublayer thicknesses, as well as Co sublayer thickness. Some of the films showed good properties for magneto‐optical medium, such as large perpendicular magnetic anisotropy and Kerr rotation, and perfect squareness of the magnetic hysteresis loop. The Pd‐predeposited films were found to have a remarkably high coercivity of 4723 Oe and a greatly enhanced interfacial magnetic anisotropy of 0.72 mJ/m2. The transition from in‐plane to perpendicular magnetic anisotropy took place at a Co sublayer thickness of 8.2 Å for the multilayer with Pd predeposition. Kerr rotation was inversely proportional to the Pd/Co sublayer thickness ratio, showing the maximum value of 0.12°. The magnetic and magneto‐optical properties were correlated systematically to the structural parameters of the multilayered films.

Magnetic manifestations of cation redistribution in ferrites

The effects of radiation thermomagnetic treatment (RTMT) (as compared with thermomagnetic treatment) on Co-containing ferrospinels have been investigated. The RTMT of ferrites results in the appearance of an induced magnetic anisotropy, which improves the magnetic properties, particularly the remanence, maximal magnetic permeability and hysteresis loop squareness. The effects of RTMT are most evident in ferrites containing divalent cobalt ions in octahedral sites. The induced magnetic anisotropy arises from radiation-induced diffusion of vacancies, magnetic ions and radiation defects. The role of the irradiation temperature is discussed. The use of a periodic magnetic field during irradiation is considered in order to increase the radiation stability of the hysteresis loop parameters.

Rheomagnetic properties of mixed magnetic particle suspensions

Single-domain magnetic particles are the essential ingredient of magnetic tapes, particulate recording disks and magnetic stripes. The particles are single-domain γ-Fe 2O 3, CrO 2 or barium ferrite, and non-magnetic α-Fe 2O 3 mixture. Each of these particles has intrinsic coercivity, which should be matched with the magnetic field strength of the writing element of a particular device. In this study a magnetic inductance measurement with low field strength was employed to obtain the magnetic permeability of suspensions containing two of the particle types mixed together as a function of composition and volume fraction of particles. The bulk magnetic property B is a linear combination of the contributions from each particle type such that the “excess” inductance is L − L s = Σφ iB i where φ i is the volume fraction and B i , is the magnetic property of particle type i. For the non-magnetic α-Fe 2O 3, B i = 0. This allows the formulation of mixed particle suspensions to obtain a desired property for custom-designed magnetic particle coatings. However, mixing magnetic particle types will broaden or produce a bimodal switching field distribution. This may affect the squareness of the magnetic hysteresis loop. These properties should be taken into account for the design of a practical magnetic coating with mixed particle suspension. Another requirement of the magnetic particle suspensions is that they remain well dispersed, even though strong magnetic forces between the particles promote flocculation. An extension of the inductance measurement technique is employed to study the flocculation of a suspension containing magnetic γ-Fe 2O 3 and non-magnetic α-Fe 2O 3. The presence of the α-Fe 2O 3 decreases the flocculation state of the suspension. Thus the suspension stability is enhanced by incorporating a small amount of non-magnetic particles in addition to surfactant.

Magnetic properties and structure of sputtered Co/Pd-Ag multilayers

We have used magnetron sputtering to deposit Co/Pd-Ag multilayers onto unheated (111) Si substrates. The influence of Ag concentration on their structure, coercivity, and hysteresis loop squareness was studied. The best rectangular characteristics and highest coercivity were obtained for the films with 4.0 at. % Ag. These multilayers indicate considerable improvement in the magnetic properties necessary for magneto-optic recording media compared with Co/Pd films. The role of tensile stress in the system is pointed out and discussed.

Thermal stability of Pt/Co multilayered films

The thermal stability of Pt/Co multilayered films with various underlayers has been studied by annealing up to 400 °C. In Pt/Co films sputtered on glass or amorphous AlN underlayers, their coercivity and the squareness of magnetic hysteresis loops are degraded by annealing above 300 °C. In contrast, in films sputtered on ZnO or Pt underlayers, the coercivity is remarkably increased by annealing at 300 °C. The film with the ZnO underlayer shows a hysteresis loop with perfect squareness even after annealing at 400 °C. The results of x-ray diffraction indicate that the ZnO underlayer not only enhances the fcc Pt/Co(111) orientation but also prevents the decay of the multilayered structure during annealing. The results of laser microannealing using a conventional disk drive system also indicate that the Pt/Co films with ZnO underlayers have superior resistance to laser damage.

Microstructural investigations of Bi doped Fe garnet thin films for magneto-optical recording

Gd1.6Bi1.4Fe3.8Ga1.2O12 garnet films for short wavelength magneto-optical recording are investigated. These films have high Faraday rotation (up to 1.3 °/μm), good corrosion resistance and good magnetic properties (Hc≳1 kOe with hysteresis loop squareness of 1) but poor noise performance. This paper shows that the noise is a result of the grain size being of the order of the recorded domain size and that the grain size and distribution are determined by the initial density of garnet nuclei. In the course of this study, it was discovered that these films contain a high density of Bi globules which precipitate out of the garnet matrix. It is believed that these globules contribute to the high coercivity of sputtered garnet films.

Magnetic and magneto-optic properties of Bi-substituted garnet films crystallized by rapid thermal processing

A new technique to crystallize as-deposited, amorphous phase in (BiDy)3(FeGa)5O12 films is presented. This technique employs heat pulse annealing and leads to improved surface smoothness and smaller grains, in comparison with conventional oven anneal and also with in situ crystallization during deposition. Rapid thermal annealing was accomplished in a heat pulse apparatus with a ramp-up rate up to 50 °C/s. Upon heating for several seconds at about 650 °C, a single phase of garnet is formed. The samples were polycrystalline, but exhibit a perpendicular magnetic anisotropy of 104 erg/cm3, and a high squareness of Faraday hysteresis loops. The coercivity is typically 1–4 kOe. A systematic study of the effect of a ramp rate on a microstructure and magnetic properties has been made. The result indicates that the ramp-up rate is a key to controlling grain size and surface morphology.

Square-loop cobalt/gold multilayers

Multilayers of Co and Au with perpendicular hysteresis loop squareness ratios of ∼1 have been prepared by e-beam evaporation. These films have perpendicular anisotropy in the as-deposited condition in contrast to other work in which Co/Au multilayers, prepared by ion beam sputtering, showed perpendicular anisotropy only after annealing at 300 °C. The Faraday rotation of these square-loop multilayers is about 9×105 deg/cm of Co or 1×105 deg/cm of total thickness at a wavelength of 633 nm. These values indicate an enhancement of the Faraday rotation of Co at this wavelength by about a factor of 2. This may be a plasma-edge enhancement effect similar to that reported by Katayama et al. [Phys. Rev. Lett. 60, 1426 (1988)] in the Kerr effect of Fe/Au multilayers.

Magnetic properties of materials, transition shapes, and digital recording properties

Calculations show that the inner and outer parts of recorded magnetization transitions depend in different ways on the magnetic hysteresis properties of recording media. Thus, media with identical values of remanence, coercivity, and thickness but having different hysteresis loop shapes can have different recording properties, and these differences are more involved than just simple considerations of the effects of hysteresis loop squareness. The outer parts of transitions are shown to be significant in determining the shapes of the replayed pulses and they strongly influence the shapes of the roll-off curves.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Large Barkhausen and Matteucci effects in FeCoSiB, FeCrSiB, and FeNiSiB amorphous wires

The mechanism of the sensitive and stable large Barkhausen effects of as-cast amorphous magnetostrictive wires having three composition systems was investigated using measured values of stress-induced anisotropy constant saturation magnetostriction, residual internal stress, and MH hysteresis loop squareness M/sub r//M/sub s/. The entire composition range of FeCo is compared to FeCr with up to 10 at.% and FeNi with Ni up to 12 at.%. Matteucci effects were also investigated in magnetostrictive and nonmagnetostrictive amorphous wires magnetized with a longitudinal AC field, AC wire current, or AC field perpendicular to the wire axis.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Perpendicular magnetic anisotropy and magnetostriction of sputtered Co/Pd and Co/Pt multilayered films

Magnetic properties of Co/Pd and Co/Pt multilayers were studied as a function of sputtering gas pressure. It was found that the magnetic properties of the films depended upon the sputtering gas pressure, and large coercivity (several kOe) and a perfect squareness of the perpendicular hysteresis loop were attained by the deposition at the high gas pressure. These multilayers are suitable for perpendicular magnetic recording media. In the Co/Pd, the origin of the perpendicular magnetic anisotropy is mainly an interfacial anisotropy, although there exists a stress-induced anisotropy for the films with the relatively short periodicity. The perpendicular magnetic anisotropy of the Co/Pt can be concerned with the Co-Pt mixture formed at the interface of the multilayer structure. The magnetostriction of the Co/Pd films with the relatively short periodicity is extraordinarily large with a negative sign, since Co atoms adjacent to Pd atoms at the interface could induce larger magnetostriction than that of pure Co. As the periodicity increased, the magnetostriction became small, but the sign remained negative. For the films with the long periodicity the magnetostriction may be caused by pure Co of the layer interior. On the contrary, the Co/Pt films have a positive magnetostriction even for the thick Co layers. The data indicate existence of the Co-Pt mixture at the interface.