Mechanically induced anisotropy and its effect on magnetic permeability in single crystal ferrites

Magnetic anisotropy and initial permeability in worked Mn-Zn and Mn-Fe ferrite single crystals are investigated in connection with the average magnetostriction constant λs. These data are compared with those obtained for etched specimens. Induced anisotropy is observed for all of the worked specimens and is proportional to λs, i.e., its origin should be the magnetoelastic energy λσ induced by stress σ remaining in the worked specimens. The ratio of initial permeability, μi(as-worked)/μi(etched), at room temperature, is found to increase with increasing λ111in a low frequency range and to be greater than unity when |λ111/λ100|> 3. The second peak in μi- T curves shifts with lapping to lower temperatures for the specimens with |λ111/λ100|<3, while to higher temperatures where |λ111/λ100|<3. Such phenomena are discussed in terms of domain wall energy affected by lapping-induced anisotropy.     

Submicron bubble garnets and their characterizations

New Submicron (0.5-1.0 mum diam) bubble garnets have been developed. In order to reduce saturation induction4piMsas low as possible, suitable choice of amounts of nonmagnetic ions substituting for ferric ions in both tetrahedral and octahedral sites were studied in (YSm)3(FeAl)5O12, (YSmLu)3- (FeGaSc)5O12, (YSmLu)3(FeAlSc)5O12and (LaLuSm)3- (FeGa)5O12garnet systems. For example, in (YSmLu)3- (FeAlSc)5O12a film with the following properties was grown; strip widthw = 0.7mum, film thicknessh= 0.7mum, quality factorq=2.8, Curie temperatureTc= 140degC and4piMs=770G. The temperature properties of those films could be improved drastically by doping with a small amount of Gd ion. Wall mobilities μw of those films are in the region from 200 to 500cm/s/Oe. Preceding these material studies, several film characterization methods have been investigated. Film thickness was measured by Fluorescent X-ray method, strip width by using a highly sensitivity TV camera, and bubble collapse field by FMR resonance technique respectively.     

Influences of sputtering gas pressure on microtexture and crystallographic characteristics of Ba-ferrite thin films for high density recording media

Ba-ferrite films with small c-axis dispersion angle Δθ50are suitable for ultrahigh density recording media. The dependences of partial oxygen gas pressure PO2and total discharge gas pressure PTotalon the characteristics of Ba-ferrite films were clarified. It was found that there were three regions, where films were composed of single layer of spinel type ferrite(PO2≤0.002mTorr), mixed layer of spinel and magnetoplumbite type ferrites (0.003 leq P_{O2} leq 0.2mTorr) and single layer of magnetoplumbite type ferrite (PO2>0.3 mTorr). In the range of P02between 0.005 and 0.2 mTorr, spinel-like ferrite layer plays very important role as an underlayer to decrease the Δθ50of the Ba-ferrite layer. Films deposited at relatively low PO2and PTotalexhibit very smooth surface and Δθ50as small as2.5sim3.5deg.     

Difference between temperature dependences of both initial permeability and maximum permeability of sendust alloys

The temperature dependences (-10-50°) of the initial permeability (μ5), the maximum permeability (μmax), and the coercive force(Hc) of Sendust alloys (Fe-9 to 10 wt% Si-5 to 7 wt% Al) continuously cooled to room temperature, were investigated. Most of the studied alloys gave at least one peak value for both μ5and μmax, in the studied temperature range. The temperature giving the peak μ5agreed well with that of μmax(an effective permeability at an alternating field): the peak temperature of μeffseems to correspond to the temperature giving a zero magnetocrystalline anisotropy constant (K1= 0). The relationship between temperature and μ5was not always the same as that between temperature and μmax. From the compositional dependence of μmaxat various temperatures (10-30°C), the zero polycrystalline magnetostriction constant (λs = 0) line of the ternary Sendust alloys at each temperature could be evaluated. It is clarified that μ5of the alloys with K1< 0 is determined by both K1and λs, whereas μmaxis primarily determined by λs. When K1changes with temperature from a negative to a positive value, both μ5and μmaxof the alloys markedly decrease, independently of λs.     

A magnetic bubble passive time-slot interchanging gate

The design and operation of a magnetic bubble logic gate, able to perform the basic retardation operations for a magnetic bubble PCM time-slot interchanger,are reported. With this design no external current pulses are needed to perform those functions. With a 32 µ circuit periodicity and using (SmY)3(GaFe)5O12, bias field marginsashigh as 11.5% for the passive logic function are reported in a 25 Oe rotating field. Because no precautions are taken againsthard bubbles the unsuspicious range of frequency is limited to 20 kHz. Nearly no difference is seen in operating margins between low andhigh frequencies. Design rules are given that canlead to other bubble-to-bubble logic circuits with high operating margins.     

Magnetic properties of amorphous (fe, ni)80B20, (fe, ni)80B19si1, and (fe, ni)80P14B6alloys

Magnetic measurements were performed on amorphous (Fe, Ni)80B20, (Fe, Ni)80B19Si1, and (Fe, Ni)80P14B6alloy ribbons to yield the values of the magnetic moment per transition metal atom at 0 K and the Curie temperature. A close fit to the moment data, obtained by allowing not only the moments on Ni and Fe atoms to vary with Fe concentrationx, as revealed by neutron diffraction in crystalline alloys, but also the number of electrons per atom npand nbthat P and B atoms, respectively, donate to the transition metaldbands as described by the relationsn_{p} = 1.74 + 0.75 (1 - x)andn_{b} = 0.58 + 1.20 (1 - x), suggests a moment of 0 andsim0.13 mu_{B}per Ni atom in amorphous Ni80P14B6and Ni80B20alloys, respectively. The functional dependence of the Curie temperature onx, when followed closely for low Fe concentrations, gives the critical concentration xcabove which ferromagnetism appears in amorphous FexNi80-xB20and FexNi80-xP14B6alloy series asx_{c} cong 5and 8 at % Fe, respectively. The results of a theory based on coherent-potential approximation have been fitted to the measured values of Curie temperature in order to arrive at the Fe concentration dependence of the exchange interaction (JNiNi) between Ni-Ni pairs. The physical significance of the variation of JNiNiwithxobtained thereby has been discussed.     

Growth and properties of garnet films for storage application

A discussion of the growth of garnet films by liquid phase epitaxy without rotation of the substrate is presented for magnetic garnet layers used as materials for bubble [(YSm)3(FeGa)5O12; (YLa)3(FeGa)5O12] and magneto-optical memories [(GdBi)3(FeGaAl)5O12]. The background of the experimental and compositional approach is given.     

A comparison of frequency limited bubble device performance and material characteristics

We have observed the propagation margins as a function of frequency and temperature for a simple half-disk type test circuit fabricated on an (YSmLuCa)3(FeGe)5O12film. We have also measured the temperature dependence of the stripe width, anisotropy field, collapse field, mobility and dynamic coercivity. The frequency dependence of the margin demonstrates that in this circuit, the material is velocity limited above 300 kHz. In the range -20°C to +60°C, the upper and lower margin limits at a given frequency track the collapse field. Over this same temperature range, the mobility varies from 500 to 850 cm/sec-Oe and we conclude that the mobility is not the parameter which limits the device performance. The calculated saturation velocity is independent of temperature in this region and we propose that it is responsible for the failure of the circuit at the highest frequency. In the range from -20°C to +60°C, the coercivity becomes appreciable and the circuit performance deteriorates due to a decrease in the effective drive field.     

Contiguous-disk bubble domain devices

Contiguous-disk bubble devices are an approach to higher bit density through the use of coarse overlay patterns in manipulating small bubbles to relax device lithography requirements. As a first step towards such an objective, a fully processed chip using ion-implanted devices has been tested, showing the feasibility of all required memory functions with 5-μm bubbles and 25-μm period overlay patterns. A critique of permalloy versus implanted contiguous-disk devices is made, pointing out their basic difference in magnetization reversal processes and explaining the superiority of the latter over the former in achieving a good edge affinity of bubbles. The requirements for a good implanted device are reviewed, including the selection of garnet material parameters (K1, λ111), of implantation parameters (ion energy and dosage) and of device pattern geometry (thickness and shape of implanted layer). An understanding of these requirements has made it possible to demonstrate 1-μm bubble propagation in several contiguous-disk type circuits with 4.5-μm periods, yielding an areal density of over 3 × 10⁷bit/in²made by conventional photolithography.     

Uniaxial and cubic anisotropy constants in ion-implanted Sm,Tm,Ga:YIG bubble thin films

The effects of ion implantation into (SmTmY)3(GaFe)5O12garnet thin films have been studied by ferromagnetic resonance. He+ ions were used for implantation with doses ranging from 3 to 4 × 10¹⁵He+/ cm²and implantation energy ranging from 150 to 175 Kev. The uniaxial and cubic anisotropy constants have been studied as a function of temperature from 0°C to 100°C for both as-grown and ion-implanted films. The implantation has effectively changed an easy-axis anisotropy to that of an easy plane in the implanted layers of the films. A cubic anisotropy constant K1with values varying from 4 × 10³to 6 × 10³erg/cm³at room temperature has been observed in these films. The results also indicated that to the first order, the implanted region in the film was essentially magnetically uncoupled from the bulk of the film.     

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.     

Metallographic study on Nd-Fe-Co-B sintered magnets

Metallographic study has been carried out on the Nd-Fe-Co-B alloys to clarify the change in coercivity with the Co composition substituted for Fe in the Nd2Fe14B type sintered magnets. The decrease in coercivity caused by the Co substitution is attributed to the formation of soft-magnetic phases such as Nd(Fe, Co)2and Nd(Fe, Co)3. The mole ratio of Nd to (Fe+Co) of these soft-magnetic phases decreases with increasing the Co substitution. The Co concentration is much higher in these soft-magnetic phases than in Nd2(Fe, Co)14B matrix. The A1 addition in Nd-Fe-Co-B magnet makes the Nd(Fe, Co)2compound unstable to form the non-magnetic Nd3(Fe, Co, Al) compound, resulting in the increase in the coercivity of Nd-Fe-Co-B magnet.     

Influence of R1parameter {=Fe2O3/(Y2O3+ Sm2O3+ Lu2O3)} on magnetic bubble properties of (YSmLuCa)3(FeGe)5O12

The influence of R1{=Fe2O3/(Y2O3+Sm2O3+Lu2O3)} in the melt composition on film properties, and growth characteristics, has been investigated for (YSmLuCa)3(FeGe)5O12. The garnet phase is the primary phase when R1is kept between 10 and 60. The temperature coefficient for the bubble collapse filed changes from -0.29 to -0.19 %/°C, and the growth rate with 10°C supercooling changes from 0.60 to 0.15 μm/min, by increasing R1=10 to 60. Distribution coefficients, K^Y, K^Sm, K^Luand K^Geincrease, and K^Feand K^Cadecrease, with increasing R1.     

Magnetic interactions in pseudobinary rare earth-3d intermetallics

Magnetic measurements on pseudobinary intermetallic compounds of the series R(MnxFe1-x)2(R = Y, Gd, Er) R6(MnxFe1-x)23(R = Y, Gd, Tb, Dy, Ho, Er, Tm) R2(FexCo1-x)17(R = Y, Gd, Dy) R2(FexNi1-x)17(R = Y, Gd) are reported. Magnetization and susceptibility measurements have been performed at temperatures from 4 K to 1500 K. The magnetic interactions between Mn and Fe are discussed in terms of a localized-moment model. In the case of the R2(FexM1-x)17(M = Co, Ni) compounds, a band model seems to be more appropriate. Mössbauer Fe⁵⁷spectra obtained on the R2(Fe,Co)17series can be explained by a superposition of four different six-line patterns corresponding to the four crystallographically nonequivalent 3d sublattices.     

Spectrum and lineshape of bubble-lattice resonance

Spectral analysis of photometrically detected bubble-lattice oscillations reveal resonance frequencies of 45 and 66 MHz in a 6.2μm film of (Gd,Y)3(Fe,Ga)5O12. Similar results are obtained for stripe lattices. Existing theory explains the dependence of the lower-frequency resonance on bias field and lattice parameter. To explain the higher resonance, a theory of flexural wall vibration for plane walls associates the resonances with wave functions having zero and two nodal lines lying parallel to the film, respectively. We conclude that the amplitude of the main mode is greater at the surfaces than within the interior of the film. Characteristic fold-over and clipping of resonance line shapes are noted and discussed.     

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.     

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.     

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.     

High density recording with perpendicular Co-Cr-Nb media and ring heads

Effective double layer structure was investigated by adding Nb to the sputtering source of Co-Cr thin film perpendicular magnetic recording tapes. The output from the tapes was measured with a ring head through to the short wavelength, λ50=0.19 μm (D50=267KFRPI).     

Magnetic moments and curie temperatures of (Fe, Ni)80(P, B)20amorphous alloys

The magnetic moment per transition metal atom at 0°K and the Curie temperature were obtained for a series of (Fe, Ni)80(P, B)20amorphous quenched alloy ribbons. Fe/Ni and P/B compositions were varied separately. The moment data can be fitted well by assigning 2.1 Bohr magnetons per Fe atom and 0.6 per Ni atom, with the moment being lowered by 0.3 per B atom and 1.0 per P atom. Alternatively, moments varying with composition, as shown by neutron diffraction in crystalline alloys, combined with a lowering of 1.2 per B atom and 2.1 per P atom, also fit well. For a given P/B composition, Tcshows a broad maximum at Fe:Ni of about 3:1. For a given transition metal composition, Tcincreases with increasing B content.