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     

Directional solidification of Co-Cu-R permanent-magnet alloys

Co-Fe-Cu-Ce permanent-magnet alloys have been prepared by directional solidification using a modified Bridgman technique. Samples melted at low superheat temperatures (DeltaT sim 20degC above the melting point of about 1100°C) and solidified at moderate rates (∼2.3 cm/h) resulted in a reasonably homogeneous columnar grain structure with a preferred crystallographic orientation. Thecaxis is generally aligned within 15° of the growth axis. Increasing the speed of solidification led to a fine-grained structure with no texture, while decreasing the speed led to coarse columnar grains with erratic orientation. A large superheat temperature (DeltaT sim 300-400degC resulted in a reaction of the liquid with the alumina crucible wall and led to the formation of face-centered cubic Co-rich dendrites. With the modified Bridgman technique, oriented samples 8 cm long and 2.54 cm in diameter have been prepared with good magnetic properties. After annealing at 1000°C followed by aging at 400°C, a Co3.5Fe0.5CuCe alloy exhibited values ofiHc= 7000 Oe, Br= 6100 G, and(BH)_{max} = 9.2MG.Oe. A Co3.6Fe0.5Cu0.9Ce alloy exhibited values ofiHc= 6000 Oe,B_{r} = 6250G, aud(BH)_{max} = 9.5MG.Oe after similar treatment.     

Formation and magnetic properties of Fe-B-Si amorphous alloys

The magnetic properties and crystallization temperatures of alloys in the ternary Fe-B-Si system are reported. The Curie temperature increases slightly on replacement of boron by silicon. This results in a sharp ridge of relatively constant room-temperature saturation magnetization extending from Fe80B20to Fe82B12Si6. The coercivity exhibits a broad minimum, both before and after stress relief annealing, in the region around Fe81B15Si4and extending at least to Fe77B13Si10. The crystallization temperature increases with increasing silicon and with decreasing iron and boron. The alloys with silicon are generally easier to prepare in the amorphous state than the binary Fe-B alloys. Thus for the highest saturation magnetization alloy combined with ease of preparation, stability, and lowest losses, the alloys between Fe81B17Si2and Fe82B12Si6are preferred.     

Unusual high-frequency behavior of some amorphous metallic-alloy tape-wound magnetic cores

The behavior of several samples of amorphous metallic-alloy tape-wound magnetic cores excited under sine-wave voltage conditions in the 1 kHz to 100 kHz frequency range is investigated. These tape-wound cores made by Magnetics, Inc. from two different Allied Corporation amorphous metallic-glass alloys, METGLAS® alloy 2605S-3 (composition Fe79B16Si5) and METGLAS® alloy 2605SC (composition Fe81B13.5Si3.5C2), are studied along with Magnetics, Inc. F ferrite cores. Measurements of the induced-voltage and exciting-current waveforms are used to obtain dynamic (ac) core characteristic loops of flux density B versus net ampere turns per unit magnetic path length Npip/lm, as well as core loss. The behavior of one of the amorphous metallic-glass alloys (Alloy 2605S-3) at flux-density levels in the range of 0.5 T and 1 T is found to lead to core characteristic loops with strange shapes and to unusual variations in the plots of energy loss per unit volume per cycle versus frequency. The second amorphous alloy (Alloy 2605SC) shows similar unusual properties but only at high flux-density levels close to saturation, above 1.25 T. The unexpected behavior observed in these two alloys is due to magnetoelastic resonances of the toroidally shaped cores. By modeling the tape-wound core as a thin ring, calculations are made for the resonant frequencies corresponding to the mode of extensional vibrations which agree well with experimentally measured results.     

Rayleigh hysteresis--A new look at an old law

Experimental evidence is cited that, for very small hysteresis loops, the remanent magnetic flux density Bris not proportional to the square of the amplitude of the magnetic field excursion H1(as given by the Rayleigh relation), but rather to the first power. It is shown that (subject to one very general assumption), were this dependence exact, it would lead to negative hysteresis loss. It is also shown that (subject to the same assumption) any power-series dependence ofBonHwill always giveB_{r} propto Hmin{1}max{2}. An approximate first-power dependence is found to follow naturally from the spring model. A new Rayleigh relation is proposed which contains a logarithmic term which may not be expanded in a power series about zero argument.     

Properties of amorphous alloy films mainly composed of Co--Nb

Amorphous alloy films, mainly composed of Co-Nb, have been studied by radio frequency (RF) sputtering. These amorphous films having small magnetostriction show excellent soft magnetic properties after the magnetic annealing we have developed. One of them with the composition of (Co83.5Fe2)92/85.5Nb8was found to have very high saturation magnetizationB_{s} = 14300(gauss). The effects of additives such as Zr to the alloys have been investigated and amorphous films having high crystallization temperature as well as high saturation magnetization were successfully obtained. These amorphous films show fairly good wear and corrosion resistance as well as excellent thermal stability of the magnetic properties.     

Temperature dependence of the effective permeability of heat treated Sendust alloys

The temperature dependence (-10°C-70°C) of the effective permeability (μeff) of Sendust alloys (Fe-9-10 wt% Si-5-7 wt% Al) quenched at a room temperature from the various temperatures (400°C-700°C) was investigated at every 2°C in the temperature range of -10°C to 70°C. Most of the studied alloys gave a peak of μeffin the studied temperature range. The peak temperature (Tp) giving the peak μeffvaried with different alloy composition. The alloys of Tp = 20°C are supposed to correspond to the alloys of the zero magnetocrystalline anisotropy constant (K1= 0) at 20°C. The deduced K1= 0 lines at various temperatures (-10°C-50°C) were obtained for an Fe-Si-Al ternary system. The values of peak μeffat the same Tp were different, depending on alloy composition, This difference is due to the difference in the polycrystalline magnetostriction constant (λ s) of the alloys. The peak temperatures of the studied alloys vary with the different heat treatments. This variation is due to the variation of K1, induced by the change in microstructures of the alloys. The variation of the values of peak μeffwith heat treatments was small compared to the difference of those in the alloys of different composition. It seems that the variation of the λ s with heat treatments would be small. Both the compositional dependence of μeffat 20°C and the temperature sensitivity (Δμeff/ΔT) were obtained for both the alloys cooled continuously to room temperature and those quenched at room temperature from 400°C.     

Au-Fe-Ni permanent magnet alloys

A gold permanent magnet for an ornamental material is developed in the Au-Fe-Ni system. It is found that the magnetic properties of the An-12.5 wt% Fe-12.5 wt% Ni alloy aged at 450°C for seven hours and cold-swaged by 92 percent are Br = 0.53 T (5300 G), iHc = 40.8 kA/m (510 Oe), and (BH)max = 9.1 kJ/m³(1.1 MGOe). The Au-12.5 wt% Fe-10 wt% Ni-2.5 wt% Co alloy aged at 450°C for 2.5 h and swaged by 86 percent attained Br = 0.54 T (5400 G), iHc = 42.4 kA/m (530 Oe), and (BH)max = 9.6 kJ/m3(1.2 MGOe). In these alloys, the magnetic hardening is due to the fine Fe-Ni rich ferromagnetic particles precipitated in the Au matrix.     

Magnetic anneal anisotropy in amorphous alloys

The uniaxial magnetic anisotropy Kuinduced by a magnetic anneal has been determined, after stress relief, for a series of alloys given by (FeyNi1-y)80B20. For all of these alloys Kudepends on anneal temperature as predicted by directional order theory. The concentration dependence of Kuin these alloys is also consistent with directional order theory. The maximum Ku, corrected for its temperature dependence, occurs at the compositiony = 0.5. However, Kudoes not fall to zero aty = 1as predicted if directional order is assumed to arise only from Fe-Ni pair ordering. These results are interpreted as suggesting a role of the glass former, boron, in the directional ordering, perhaps as an "interstitial." The interaction energy derived from the results is negative as expected for interactions leading to precipitation. Its large value ofapprox -7.5 times 10^{-14}ergs corresponds to a critical temperature for precipitation of 3000 K.     

Rare earth - transition metal alloys: Another way for perpendicular recording

Many investigators have chosen CoCr alloys or other Co-based alloys to study perpendicular magnetic recording. Although the perpendicular magnetic anisotropy of Co alloys is quite convenient for this use, the demagnetizing fields are high because of high saturation magnetization and then the squareness of the perpendicular M-H loops is poor. To study another kind of perpendicular anisotropic alloy, we tested sputtered amorphous Fe1-x-yTbxGdy(X = y) thin films as a perpendicular recording medium. Several thicknesses with and without a FeNi underlayer were tested. Although a conventional ring-type head was used, with a low trackwidth (20 μm) and a coil with 2 × 13 turns, 162 KFci could be recorded and read and a 1,600 μ Vpp output signal was read at 10 KFci.     

Corrosion-resisting Co-Pt thin film medium for high density recording

This paper describes a new material medium for high density longitudinal recording. Sputtered Co-Pt thin films will be shown to have excellent corrosion resistance and magnetic properties. Co-Pt thin films do not need a thick overcoat like plated Co-Ni-P films do, and have higher remanent flux density than ferrite thin films. Co1-xPtx(X=0-0.60) thin films prepared by r.f. diode sputtering have a maximum Hc value near X=20. The Hc, Bs and squareness, for 20 at.% Pt film are 1,100 Oe, 12,000 G and 0.80-0.90, respectively, at 0.1 μm film thickness. These values are not changed over 1-15 Watt/cm²power densities, corresponding to 6-85nm/min deposition rates. Films with more than 28 at.% Pt have no Bs change after immersion in water for over one month, indicating that the films are passive by this test, at least. Ni additions improve magnetic and corrosion properties. There is no Bs change for Co0.070Ni0.010Pt0.020films after immersion in water for over one month. Finally, 51 KFRPI linear recording density was obtained, at D50, using a Co0.70Ni0.10Pt0.20thin film disc with a 0.46 μm gap length head and a 0.12 μm head-medium spacing.     

Behavior of perpendicular recording materials in Cl and S containing atmospheres

The corrosion behavior of Co-Cr and Ni-Fe alloys is reported after exposure to Cl2, SO2, and O2containing test atmospheres at various relative (RH) humidities. Surface Chemistry, physical features, and magnetic properties were characterized. The Ni-Fe alloys exhibited excellent corrosion resistance in elevated RH atmospheres. Co-Cr alloys showed little change in magnetic properties even when significant chemical penetration of the film occurred. Substrate chemical composition proved to be an important factor in sputtered film corrosion behavior.     

Ferro-antiferromagnetic transition in the alloy system Fe65(Ni1-xCrx)35at low temperatures

The magnetic and electric properties of iron-nickel "invar" alloys and stainless steels are measured at low temperatures. It is shown that "invar" alloys such as stainless steels exhibit one-directional anisotropy, and their electric and galvanomagnetic properties are rather specific. It is shown also that the concentration dependence of Neel temperatures and magnetoresistance for the systems Fe-Ni and Fe65(Ni1-xCrx)35are similar.     

Uniaxial anisotropy by "radiomagnetic" treatment; controlling factors in a new process

A new process-an electron-"radiomagnetic" treatment-for obtaining high-remanence, low-coercive-force loops in magnetic alloys was recently announced. As an example, 2-MeV electron irradiation of 6-mil-thick ring laminations of polycrystalline 5-80 Mo Permalloy with 10¹⁷e/cm²in an applied circumferential magnetic field of 0.2 Oe atsim100degC produced record highs in remanence (∼6700 G) for this material. Additional studies of this process have been made to determine some of the controlling factors and the range of application. In particular, the effects of the dose (number of e/cm²) and of the preirradiation magnetic properties were examined. The results show that: 1) for a given dose of1.1 times 10^{17}2-MeV e/cm², the relative change in remanence (DeltaB_{r}/B_{r}) is always positive, ranging from 10 to 50 percent, but varies inversely with the preirradiation value of remanence (Br); 2) for the same dose, the relative change in coercive force (DeltaH_{c}/H_{c}) also depends upon the preirradiation value of remanence, but in a different way. ForB_{r} < 5000G,DeltaH_{c}/H_{c}is either negative or zero. ForB_{r} > 5000G,DeltaH_{c}/H_{c}is positive, ranging from 20 to 150 percent, and increases linearly withB_{r}; 3) if the dose is reduced tosim0.8 times 10^{17}e/cm², thenDeltaH_{c}/H_{c}is reduced to a tolerable level (∼10 percent) with no significant sacrifice in the positive gain in remanence and rectangularity. Hence, there are optimum dose ranges in the "radio-magnetic" treatments of alloys, where significant gains in remanence may be obtained without appreciable increases in coercive force.     

A new method for fast and efficient magnetic selection of hard Ferrites

A new method for fast and efficient magnetic selection of hard ferrites is described in which a procedure of magnetization with transient periodical oscillations (MTPO) is used. This method was evaluated during the determination of remanent induction Brand coercive forceBHcof hard ferrites. The equivalent circuit of an instrument for magnetization, measuring, selection, and demagnetization (MMSD) using the MTPO procedure also is given.     

Development of cost-effective nanocrystalline multi-component(Ce,La,Y)-Fe-B permanent magnetic alloys containing no critical rare earth elements of Dy,Tb,Pr and Nd

Here we first report the fully abundant rare earth(RE)-based nanocrystalline multi-component(Ce,La,Y)-Fe-B alloys containing no critical RE elements of Nd,Pr,Dy,and Tb by melt-spinning technique.The roles of La and Y substitutions for Ce have been fully understood.La plays a positive role on both thermal stability and room-temperature(RT)magnetic properties.The enhanced coercivity Hcj by partial substitution of La is attributed to the increases of anisotropy field HA and the formation of continuously distributed grain boundaries resulting from the suppression of CeFe2 phase.Although Y substitution is not benefit for Hcj,both remanent polarization Jr and thermal stability have been effectively improved since Y2Fe14B shows relatively high saturation magnetization Ms and a positive temperature coefficient of HA over a certain temperature range.In addition,RE element segregation has been confirmed,La prefers to enter into the grain boundaries than Ce and Y prefers to remain in the 2∶14∶1 phase.Based on these understanding,a series of melt-spun(Ce,La,Y)-Fe-B alloys have been designed.A relatively good combination of magnetic properties with maximum energy product(BH)max=7.4 MGOe,Hcj=400 kA/m,and Jr=0.63 T has been obtained in[(Ce0.8La0.2)0.7Y0.3]17Fe78B6 alloy,together with high Curie temperature(Tc=488 K)and low temperature coefficients of remanence(α=-0.255％/K)and coercivity(β=-0.246％/K).     

Preparation by sputtering of thick sendust film suited for recording head core

A 12 μm thick film with large saturation flux density, 11 000 G, and high effective permeability, such as 240 at 20 MHz, was prepared by using tetrode sputtering equipment from a ternary alloy that consisted of Si:10.5 wt.%, Al:5.6 wt.%, and Fe:bal. (Si rich Sendust alloy) at a target voltage of 1000 VDC. These were the best conditions for obtaining the minimum value of coercivity with the glass substrate in our experiments. The electric resistivity and Vickers hardness of the film became greater than the same qualities in bulk alloys. The increase in effective permeability at high frequencies, and the higher resistivity and hardness are believed to originate from the granular structure of the film. In this study, it was proved that the magnetic properties, especially the coercivity and the initial permeability of the film were due, not only to the effect of magnetostriction and crystalline anisotropy, but also to the effect of film structure.     

Investigation of Nanocrystalline Fe-Cu-Nb-Mo-Si-B Alloy

The soft magnetic properties are reported for newly-developed nanocrystalline Fe72.7Cu1Nb1.8-Mo2Si13B9.5 and Fe73Cu1Nb1.5Mo2Si13B9.5. The high frequency core losses of the new alloys are as follows: P3/100K=473 kW·m-3, P2/200K=750 kW·m-3, P2/500K=3400 kW·m-3,P0.5/1000K=680 kW·m-3, which are clearly lower than those of the early-developed Fe-Cu-Nb-Si-B nanocrystalline alloys and the superior power MnZn ferrite H7.4. The dependences ofcore loss on frequency and amplitude magnetic flux density have been analysed. The temperature relations of initial susceptibility have been examined for as-quenched and different annealedFe72.7Cu1Nb1.8Mo2Si13B9.5 alloy and interpreted by using the phenomenological theory.     

The role of microstructure in the mechanical behaviour of Ti-1.6 wt.%Fe alloys containing O and N

The effects of small changes to the heat treatment temperature within the (α + β) phase field on the room temperature properties of a Ti-1.6 wt.%Fe-0.56 wt.%O-0.04 wt.%N alloy are described. To identify contributions from the individual alloying elements the binary Ti-1.6 wt.%Fe and ternary Ti-1.6 wt.%Fe-0.6 wt.%O and Ti-1.6 wt.%Fe-0.04 wt.%N alloys were also investigated. It was found that the interstitial elements affected the degree of disorder in the ω_ath phase, and that the magnitude of this disordering was not merely consistent with changes in Fe concentration. The strength and ductility of the alloys free of additional nitrogen were independent of annealing temperature, whereas the alloys containing nitrogen showed a marked dependency on the temperature. Alloys containing nitrogen displayed a prismatic rather than basal texture after processing.     

A new permanent magnet material: Modified Ca ferrite

An experiment was carried out to investigate the preparation condition of anisotropic Ca system ferrite magnets with optimum magnetic and physical properties. Compositions were chosen according to the formula (CaO.nFe2O3)100-x(La2O3)x, wherexwas varied between 0 and 4.0, and n between 5.5 and 6.25. The optimum condition of making magnets and some properties of a typical specimen are as follows. The preparation condition: composition (CaO.6Fe2O3)97(La2O3)3, semisintering condition 1250°C × 1 h in O2gas, sintering condition 1275°C × 0.5 h in O2gas. Magnetic properties:4piI_{10}k = 4200G, 4πIr = 4100 G,IHC= 2100 Oe,BHC= 2050 Oe,(BH)_{max} = 3.5MG . Oe, Ku = 3.34 × 10⁶erg/cc, HA= 20.5 kOe,sigma_{s} = 64.8emu/g, Tc = 446°C.