Grain-size dependence of coercive force in sputtered and annealed iron films

Magnetic properties such as coercive force, initial susceptibility, etc., are structure sensitive parameters. Especially, the coercive force depends on the existence of crystal defects such as dislocations and grain boundaries. In this study, the grain-size dependence of coercive force was investigated in an iron film, 150 nm in thickness, deposited by sputtering method on a (001) KCl substrate at room temperature. The grain size of the film was changed from 15 to 120 nm by annealing in a vacuum. The coercive force increased with the increase of grain size and was proportional to the square of grain size. The magnetic domain had a ripple structure when the grain size was smaller than 50 nm. A grain size larger than 50 nm led to an irregular domain wall configuration and the formation of domain walls in the grain.     

Thin evaporated films with high coercive force

A technique allowing the preparation by vacuum evaporation of a material useable as a storage medium in digital magnetic recording is described. It consists of the evaporation of successive chromium and cobalt layers on a substrate, the nature of which seems indifferent. The coercive force can be adjusted from 200 to 600 Oe by adjusting the cobalt layer thickness. Superimposing identical double layers of chromium-cobalt allows one to obtain the required amount of flux. Such a multiple layered film gives properties identical to those of a homogeneous magnetic material with a coercive force between 200-600 Oe and an induction better than 10 000 gauss. These properties are isotropic. High squareness of the hysteresis cycle, with Mr/Ms > 0.95, is achieved.     

High coercive force films of cobalt-nickel with additions of group VA and VIB elements

This paper describes some of the structure-property relations for Co and CoNi films containing Group VIB additions, i.e., chromium, molybdenum, and tungsten and Group VA additions, i.e., phosphorus, arsenic, antimony, and bismuth. All films were prepared by electrodeposition. The magnetic properties and metallurgical structure of the films with tungsten cover the same range of parameters as produced with the phosphorus films. The quantity of the elements required to achieve the maximum in coercive force increases substantially in the sequence P, As, Sb, and Bi; and in the sequence W, Mo, and Cr. The saturation moment and coercive force both decrease with increase of the concentration of added element required to attain the maximum coercive force. The quantity of the elements required is believed to be related to the ability of the electrolyte to produce a refinement of the grain size of the deposit, and the ability of the element added to segregate to the grain boundaries. The saturation moments of Co with W and P agree with the results expected for solid solutions except at high concentrations. The structure sensitive magnetic properties obtained with CoNiW films are qualitatively interpreted in the same way as for the CoNiP films, i.e., on the basis of a strongly interacting array of fine particles. The alloys containing Cr, Mo, or W possess improved resistance to aging at elevated temperatures and in corrosive environments.     

Cr migration in CoNiTa/Cr films by annealing

CoNiTa/Cr double-layered films for longitudinal magnetic recording media have been prepared by using the facing targets sputtering apparatus. Substrate heating and postannealing were performed in order to increase the coercive force H_c. While the as-deposited film at the substrate temperature T_s of 400°C had H_c of 780 Oe, the films deposited at T_s of room temperature, exposed to atmosphere, and annealed at 400°C, had H_c as high as 1700 Oe. It has been found that the same amount of Cr atoms migrated from the underlayer to the magnetic layer and the vicinity of the film surface. Consequently, such a large increase of H_c seemed to be caused by isolation of magnetic grains by Cr atoms in their boundaries     

The effect of initial growth layer on magnetic properties of Co-Crfilms

The effect of a Ti underlayer, which increases the perpendicular coercive force of Co-Cr films, was investigated. To clarify the cause of this phenomenon, the film-thickness dependence of the magnetic properties was examined. It was found that the coercive force of a Co-Cr film deposited directly on a polymide substrate decreases drastically when it becomes thinner than 50 nm, whereas in the case of Co-Cr film on a Ti underlayer, a high coercive force is maintained even when the film becomes as thin as 20 nm. The film with the underlayer has a distinct uniform columnar structure, whereas the film without it has a 50-nm-thick initial growth layer with no clear structure. Measurements of the temperature dependence of magnetic properties and observations of segregated microstructures indicate that the improvement of magnetic properties by the insertion of the Ti underlayer is mainly due to the improvement of shape anisotropy resulting from the formation of a distinctly segregated microstructure     

A ballistic method of determining a hysteresis curve by means of short current pulses

Summary The suggested new ballistic method of obtaining a hysteresis curve for materials with a small permeability has a number of advantages as copared with the conventional ballistic method. Magnetization by means of current pulses provides a current density in the magnetizing winding of the sample 400 to 500 times higher than normal and greatly simplifies the conditions of magnetization and measurement. Moreover, the sample does not heat up during measuring, which often occurs in the conventional ballistic method.The hysteresis curves obtained by the new method for a steel with a coercive force of 24 amp/cm and for an aluminum-nickel alloy with a coercive force of 512 amp/cm coincided with the curves obtained by other methods.     

Preparation and hard magnetic properties of Co-Zn-P films for high-density recording

The digital recording density of magnetic media can be improved by the development of thin ferromagnetic coatings having a high coercive force. An experimental study of the influence of zinc on the coercive force of chemically reduced cobalt-phosphorus films is presented. Incorporation of zinc increases the coercive force of cobalt-phosphorus films on Mylar substrates by a factor of 2 to 60. Cobalt-zinc-phosphorus films exhibited coercivities ranging from 300 to 1200 Oe, depending on the preparation conditions. The influence of substrate and solution parameters, such as hypophosphite ion concentration, zinc concentration, and pH are discussed with respect to the hysteresis properties of the films. The influence of zinc on the coercivity is attributed to increased magnetic isolation of the cobalt particles and to a modification of particle size.     

Facing targets type of sputtering method for deposition of magnetic metal films at low temperature and high rate

A new type of cathode sputtering apparatus with two targets facing each other has been developed to prepare magnetic films at a high deposition rate without the extreme rise of the substrate temperature. When two disks of iron and nickel were used as targets, the maximum deposition rates obtained were approximately 4000 and 5000 Å/min, respectively. The substrate temperature was not elevated above 200°C during sputtering. The high rate deposition of Mo permalloy films also was attempted by co-sputtering of two facing targets composed of disks of iron and nickel and chips of molybdenum. The Vicker's hardness of the obtained Mo permalloy films was about 900 and the typical values of permeability at 1 MHz magnetic field and coercive force at dc magnetic field of them were about 2500 and 0.16 Oe, respectively.     

A technique for measuring pole tip saturation of low inductance heads

Increasing the coercive force of a magnetic recording medium normally improves high density digital performance. However, in rigid disk systems, the head is not in intimate contact with the disk. In addition, the ferrites employed as head materials have much lower saturation magnetization than the metals normally used in other types of heads. Under these conditions, the head field may be inadequate to fully saturate recording media of higher than normal coercive force. In the development of the latest disk products, increasing the coercive force has not improved performance but has increased overwrite modulation. This situation has not been improved by increasing write current amplitude. Pole tip and core saturation of the record head has been suspected as the cause of these observations. This paper describes a method of characterizing saturation effects in low inductance heads such as those used with rigid disks. Evidence of the deterioration of performance due to pole tip and core saturation is shown from isolated pulse measurements on a rigid disk with NiZn and MnZn ferrite heads.     

The substrate influence on the magnetization of nickel electrodeposited thin films

The effects of diffusion of substrate copper atoms into the film as well as substrate stresses on both saturation magnetization and coercive force of annealed electrodeposited Ni films have been investigated.     

High rate magnetron sputtering of ferromagnetic SmCo, Fe and CoCr thin films

Ferromagnetic thin films have been sputtered from a modified conventional magnetron cathode (3" diameter). The targets (5 to 6 mm thick) were stainless steel, demagnetized SmCo5and CoCr(15-18 at% Cr). The deposition rate was 6 nm/s at a power density of 15 W/cm². Increasing the power rates up to 12 nm/s could be achieved. The saturation magnetization ranged from 0.4 to 1,5 Tesla. The films sputtered from stainless steel had a magnetization only 30 % smaller than the magnetization of Fe. The coercive force varied from 0.8 to 75 kA/m.     

Magnetic properties and longitudinal recording performance of corrosion-resistant alloy films

This paper describes the magnetic properties, recording performance and corrosion resistance of sputtered CoCr alloy films and CoCrTa alloy films. The saturation magnetization of CoCr was 525 emu/cc and not affected by substitution of a small amount of Ta. CoCrTa films exhibit greater coercive force values than CoCr films. The maximum coercive force of CoCrTa was 1400 Oe at a thickness of 400A, whereas at a similar thickness the coercive force of CoCr was 900 Oe. The coercive force decreases linearly with temperature (25°C. to 125°C.) at a rate of 3.16 Oe/°C. for CoCrTa and 1.87 Oe/°C. for CoCr. Longitudinal recording performance at -3 dB signal level was 8386 flux reversals/cm (21,300 fci) and 11,063 flux reversals/cm (28,100 fci) for CoCr and CoCrTa respectively. The alloys exhibited corrosion resistance at 80% relative humidity and 65° C. for a two-week period equivalent to at least six years under ambient disc drive conditions.     

Influence of coercive force and easy-axis bias on domain wall motion in NiFeCo films excited by hard-axis pulses

Domain wall motion in vacuum-deposited 1200 Å- 2000 Å-thick NiFe and NiFeCo films, excited by a 0.5 ns rise time/200 ns fall time hard-axis pulse field with an easy-axis dc field, is examined with regard to coercive force, easy-axis bias, and low-frequency creep results. Both NiFe and NiFeCo films have the same threshold field characteristics despite large differences in properties. The magnitude of the hard-axis pulse field necessary to cause creep increases with increasing difference between wall coercive force and easy-axis bias. Furthermore, the average creep displacement, for a given hard-axis pulse field magnitude, versus the easy-axis bias field normalized by wall coercive force results in almost identical curves for both NiFe and NiFeCo films except for a shift related to the threshold field. This result is consistent with previous low-frequency creep data and implies that the basic mechanism of low- and high-frequency creep may be closely related. The direction of the basic wall motion depends on the spin polarity in the wall and the durection of the hard-axis pulsed field. Motion in a direction opposite to the basic motion may be produced by an esay-axis bias field of sufficient magnitude but less than then wall coercive force, which is a new and significant result. A theory based on the dynamic torque equation and nonconservative spring coercive force model has been developed to explain the high-frequency creep phenomenon. This theory qualitatively predicts the observed experimental results very well.     

The effects of metallic underlayers on Properties of permalloy films

Thin Permalloy films of zero-magnetostrictive composition were evaporated on a variety of metal film underlayers of various thicknesses (which were deposited on glass substrates) and also on smooth metallic substrates. In contrast to Prosen et al., however, the observed uniaxial magnetic anisotropy is not zero. In thin Permalloy films (100-1000 Å) deposited on high melting-point metal films (Mo, Ti, Pd, and Cr), essentially the same anisotropy field is obtained as is normally observed on glass substrates. In these films the coercivity and the angular dispersion increase slightly as the underlayer thickness increases. Permalloy properties on low melting-point metals (Au, Ag, Cu, and Al) depend strongly upon the underlayer thickness. At a given substrate temperature, a maximum in coercivity and angular dispersion is found in ∼100 Å thick underlayers of Au, Ag, and Cu. In Al underlayers, the values of coercive force along the easy and hard axis increase rapidly as a function of thickness. Large values of the easy-axis skew are obtained in all metal underlayers where the direction of the skew depends upon the geometrical arrangement of the vapor source (Permalloy) and the substrate. These effects are attributed to the microstructure and morphology of the underlayers. Electron microscopy studies are presented in confirmation of these surface geometrical effects.     

Strain insensitive Ni-Co films over a wide composition range

The magnetic properties of vacuum deposited Ni-Co films have been studied as a function of film composition, film thickness, and substrate temperature. The experimental parameters ranged from 400-1000 Å for thickness 17-41-percent Ni for composition and room temperature to 300°C for the substrate temperature. It was found that the magnetoelastic strain coefficient approaches zero in the vicinity of 35-percent Ni in agreement with Tolman's result[1] and remains insensitive to film composition from 30-40- percent Ni. These results are in reasonably good agreement with calculations based on single crystal data and the expression of Callen and Goldberg [10]. The coercive force and anisotropy field are an order of magnitude larger than of nonmagnetostrictive Permalloy films. An unexpected result is an increased coercive field with increasing film thickness while the anisotropy field remains practically constant; the films become inverted at a critical thickness in the order of 750 Å For a wide variation of preparation parameters the crystallite size remained less than 100 Å     

Estimating the Mechanical Properties of Diamond-Containing Composites Using the Value of the Coercive Force

We propose to estimate the mechanical characteristics of diamond-containing composites for stone-cutting wheels made of a metallic binder with a ferromagnetic component by the coercive force. For M6-14 and M6-14-1 binders, the hardness (yield stress) depends linearly on the coercive force in the range 85–100 HRB. The value of the coercive force of a diamond-containing composite rather well reproduces its structural state, which essentially depends on the composition of the binder, the original material, the manufacturing technique, and the sintering temperature of the composite. The obtained regularities enable one to determine the optimum interval of values of the coercive force for the required level of the mechanical characteristics depending on the composition of the binder.     

Cementite dispersed in carbons from ferrocene,vinylferrocene, divinylbenzene systems

Cementite-dispersed carbon was synthesized by pressure pyrolysis of divinylbenzene-vinylferrocene and divinylbenzene-ferrocene below 600° C. The magnetization of divinylbenzeneferrocene polymer was higher than that of divinylbenzene-vinylferrocene copolymer at temperatures from 300 to 400° C. The saturation magnetization of cementite-dispersed carbon formed above 500° C was dependent only on the iron concentration in the carbon matrix. The coercive force of cementite-dispersed carbon synthesized from divinylbenzene -vinylferrocene copolymer was about 900 Oe as a maximum value, whereas divinylbenzene-ferrocene polymer gave cementite-dispersed carbon with lower coercive force of 200 Oe. The size of cementite particles dispersed in the carbon from divinylbenzene-vinylferrocene copolymer was less than 50 nm diameter, while divinylbenzene-ferrocene (DVB-Fc) polymer gave a carbon containing larger particles up to 130 nm. The feasible initial aggregation of paramagnetic species in DVB-Fc polymer gave large particles of cementite with multiple magnetic domain. Fixation of ferrocene by the carbon-carbon bond to the parent polymer matrix was found to be effective for fine dispersion of cementite particles in the resultant carbon.     

Structures and magnetic properties of Co and CoFe films prepared by magnetron sputtering

Structures and magnetic properties of Co and CoFe films on Si(100) have been investigated by employing scanning tunneling microscopy, atomic force microscopy, and magneto-optic Kerr effect techniques. As the film thickness increases, Co or CoFe clusters with different sizes are observed. As the film thickness increases below 20 nm, the size of the metal clusters decreases. For thicker films, the surface roughness increases monotonously by increasing the thickness. The easy axis of magnetization for both Co/Si(100) and CoFe/Si(100) prefers to be in the surface plane. By deposition of the Co or CoFe overlayers, the evolution of the longitudinal coercive force shows similar trend to the surface roughness. Minimum coercive force coincides with the smallest roughness of the film. For a film with greater roughness, the observation of larger coercive force could be explained by the impediment of the propagation of domain wall motion by defects of the films. At a higher deposition rate, Co islands in triangle shapes with an edge length around 100 nm are observed. This nanostructure shows an hcp-Co with the c axis parallel to the surface plane and is observed to be able to stabilize the coercive force for Co/Si(100) films.     

New longitudinal recording media CoxNiyCrzfrom high rate static magnetron sputtering system

Three new magnetic alloys A:Co64.2Ni27.4Cr8.4. B:Co74.1Ni15.9Cr10.0, and C:Co82Ni18were used as targets to sputter thin films with coercivities up to 1015 Oe, 926 Oe, and 825 Oe respectively. Chromium films were used as the base layer. With a base pressure below 2 × 10^-7torr and chromium thickness of 2500Å, the following magnetic characteristics of alloys A and B were obtained: Hc>900 Oe, Brδ>530 G-µm, S>78%, S* > 93%, S/N (at 5MHz) > 45dB and D50> 17KBPI. X-ray diffraction measurements indicate the (1011) texture of CoNiCr films is the reason for the high coercivity and squareness ratio. This orientation may result because the in-plane atom density for Co alloys HCP(1011) and Cr BCC     

Easy direction coercive force associated with domain wall motion in nickel-iron films

The origin of domain coercive force in thin nickel-iron films is of considerable scientific and technological interest. Three principal causes of domain coercive force have been suggested. These are surface roughness, inclusions, and the presence of magnetisation ripple in the films. The current theories of these contributions are outlined, and the results obtained experimentally are compared with those expected theoretically. On the basis of this comparison, it appears that all three contributions can be important. However, it is not clear how the components due to the various causes should be combined.