Ordered Fe-Pt(001) thin films on glass substrates were studied from the viewpoint of their application in future high-density magnetic recording media. A 13-nm-thick film with fine discrete domain patterns was successfully prepared by a high-pressure sputter-deposition method. The magnetic property showed a small value of Hc/Hk and a steep M-H loop, suggesting a strong exchange interaction. Judging from the high SNR for the Fe-Pt film medium, similar to that for a low noise Co-Cr22-Nb4 medium, it is concluded that the Fe-Pt medium may have high potential as a new recording medium.
The difference in the thickness dependence of the surface and volume coercivities in Co-Cr and Co-Cr-M films was investigated. Co-Cr-Y film showed almost the same thickness dependence for both surface and volume coercivities, while other Co-Cr-M films showed a large difference between them. It was found that Co-Cr-Y films have a topological structure with a maze-like pattern, showing a fine magnetic domain structure. Co-Cr-Y film is concluded to show strong magnetic coupling in the direction of the film thickness.
The structure and magnetic properties of Co-Cr-M (M = Nb, Y) thin films were studied. It was found that Co-Cr-M films show a higher perpendicular coercivity (Hc⊥) than Co-Cr films for a wide range of saturation magnetization values (Ms). A lower-Cr-content Co-Cr-Y film exhibited a high Hc⊥ with a fine magnetic domain structure showing no increase in Ms when the substrate temperature was increased. Co-Cr-Y films showed a fine structure of both grain observed by AFM and crystallite grain observed by TEM, and also showed a narrow distribution of the crystallite grain size.
The effect of a Ti seed-layer on the magnetic properties and microstmctures of CoCrTa was studied in CoCrTa/Ti/CoZrNb double-layered perpendicular recording media. It was revealed that a thin Ti film of 5 nm, deposited at a substrate temperature of 230°C, gave the most enhanced c-axis alignment perpendicular to the film plane, showing the greatest perpendicular anisotropy. This large anisotropy yielded the best magnetic and recording properties under the present experimental conditions. The read-back amplitude at this Ti thickness was 3 times larger than that without the Ti layer, resulting in a higher ratio of signal to media noise. There was no significant loss in recording resolution due to the non-magnetic Ti space between the CoCrTa recording layer and the CoZrNb underlayer.
Perpendicular/longitudinal composite media were fabricated by sputtering. It is hard to deposit a perpendicular upper layer on a longitudinal underlayer because of the epitaxy between the layers. Therefore, it is important to prevent the epitaxial growth between the perpendicular upper layer and the longitudinal underlayer. For this purpose, we attempted to apply an amorphous carbon interlayer. First, the magnetic properties of perpendicular single media with Ti-Cr and C underlayers were compared. As a result, it was found that a perpendicular single medium with a C underiayer had the same property as a medium with a Ti-Cr underlayer. In accordance with these results, a perpendicular layer was deposited onto a longitudinal layer with a C interlayer. Consequently, the thickness of the C interlayer was optimized. As a result, a perpendicular/longitudinal composite medium was successfully fabricated using 5-nm C interlayer.
The read-write characteristics of a perpendicular/longitudinal composite medium prepared by sputtering were investigated. The composite medium exhibited a higher voltage than a perpendicular single-layered medium, although the noise of these media was almost the same. The noise of the composite medium increased slightly with the recording density, suggesting that it was affected by the longitudinal underlayer. However, the noise reduction effect of the composite medium was observed by comparing with the simple superposition of the noise of each single layered medium. As a result, it was found that the perpendicular/longitudinal composite medium exhibited a higher S/N value than the perpendicular single-layered medium.
The baseline shift of perpendicular single-layered media and perpendicular-longitudinal composite media was investigated. A baseline shift was observed for both the perpendicular single-layered media and the composite media, but the extent of the shift decreased with increasing underlayer coercivity for the composite media. From the off-track profile and MFM observation, the baseline shift is considered to be caused by the remanent magnetization state around the track edge for these media. The decrease in the baseline shift with increasing underlayer coercivity for the composite media is likely to be related to the writability of these media, and it might cause a change in the remanent magnetization state around the track edge.
It had been pointed out that a small magnetic stray field can easily demagnetize written bits in a perpendicular double-layer disk associated with a single-pole writing head. The robustness of the single-pole head with respect to the stray field was therefore investigated by computer simulation based on the finite element method. The results indicated that less sensitivity, or better robustness, with respect to the stray field was attained by decreasing the permeability of the soft magnetic underlayer of the disk, which is considered to be consistent with experimental results.
Waveform of isolated pulses for single-layer perpendicular media written with a ring head was analyzed. In particular, the dependence of the peak separation and amplitude for dipulse waveforms at 2 kFRPI on the write current was investigated. Writing with a small-gap-length head at small spacing makes the magnetization transition narrower. It was easy to realize saturation recording for a medium with a steep hysteresis loop. A Co-Cr-Nb-Pt single layer medium with a soft magnetic back layer has the possibility of high-resolution recording with large output. The medium seems to become one of candidate media for a 20 Gbit/in2 area density recording.
We discuss the effect of exchange coupling on written bit stability in perpendicular media in terms of resistance to thermal fluctuations. The optimum value of exchange coupling appears to coincide with a medium in which overall interactions, as measured by the δM curve, are close to zero. We calculate the upper limit of the areal density that can be supported by our typical medium and find values of between 80 and 400 Gb/in2, depending on the bit aspect ratio.
Double-layer media with single-pole heads are ideal for perpendicular magnetic recording. However, the problem of unstable recorded magnetization due to the magnetic domains of underlayers has not yet been solved. We investigated the dependence of the signal stability of a medium with an Ni-Fe underlayer and a medium with an Fe-Si-Al underlayer on the directions of the applied magnetic fields under an SPT head-loaded condition and an ID/MR head-loaded condition. The results show that the recorded signal has better stability with a horizontal field than with a vertical field. They also show that the recorded signal has better stability under the ID/MR head-loaded condition than under the SPT head-loaded condition.
Demagnetization of written bits in a medium with a single-pole write head, namely, head-induced erasure, was investigated in perpendicular recording. The effects of using a single-pole head in combination with a double-layer medium in experiments were also studied. In this paper, we discuss the demagnetization of a medium by addition of an external field. A way of counteracting that field is suggested as a means of changing the permeability of the medium underlayer.
The influence of the damping constant α on recording characteristics at high frequencies was simulated by using the Langevin equation, with the condition that the head field rise time is constant. In the frequency range up to 190 MHz the signal outputs for α = 1 and α = 0.05 are same. On the other hand, in the higher- frequency range over 190 MHz, where the head field decreases before it reaches the maximum value, the signal outputs for α = 0.05 are larger than those for α =1.0. This is because the critical switching field depends on the damping constant α and it decreases with a lower value of α.
A series of identical Co82Cr13Ta5/Cr thin-film longitudinal media were deposited at substrate temperatures (Tsub) of room temperature (RT), 150°C, and 250°C respectively. Tracks were written at linear densities of up to 250 kfci, and the recording performance was examined An inverse relationship was observed between Tsub and noise levels. A variety of electron microscopy techniques were employed on the same films to investigate the origin of this relationship. Spin-echo nuclear magnetic resonance (NMR), TEM after wet chemical etching, and energy- dispersive X-ray (EDX) analysis reveal the existence of compositional separation in the media deposited at elevated temperatures (250°C). This causes a reduction in the intergranular exchange coupling as detected in ΔM measurements. The reduction can be directly observed in Lorentz images in the form of smaller magnetic clusters. Cluster size has a strong effect on the written tracks. Lorentz images for each medium show a strong correlation between the cluster size and the noise measured.
In this study, Sm-Co layers with various thickness were prepared at various Ar pressures and substrate temperatures on Cr underlayers and their magnetic properties and surface morphology were studied. Sm-Co layers with coercivity higher than 3 kOe can be prepared at room temperature and at Ar pressures of around 8 mTorr. The grain size, which was evaluated with AFM, is almost same as that of the Cr under layer where the thickness of the Sm-Co layer is below 100 nm. Sm-Co/Cr films with coercivity higher than 3 kOe can be prepared at thickness in the range of 15 to 100 nm. These films exhibited squareness ratios greater than 0.83 and coercive squareness ratios greater than 0.95. The experimental results suggest that Sm-Co/Cr films are suitable for use as a high density longitudinal recording medium.
Various ways of recording magnetic media for high-density recording were investigated. The main characteristics required of a medium are low noise and high coercivity. We made a low-noise medium by simultaneous sputtering SiO2 and CoPt onto a Cr underlayer at high Ar pressure and room temperature, and attempted to raise the coercivity of the medium. It has hitherto been recognized that a CoPt-SiO2 medium is not influenced by a Cr underlayer. However, we showed that the extent of the influence of the Cr underlayer changed according to the quantity of SiO2. Our medium contained 10 at% of SiO2. Recognizing that the effect of the Cr underlayer influenced the magnetic layer, we added Mo to the Cr underlayer, and were able to increase the coercivity by adjusting the crystal with CoPt and the Cr underlayer and by increasing the lattice spacing of the Cr. The medium noise was also reduced by adjustment in crystal with CoPt and Cr underlayer, and, as a result, the S/N ratio was improved at 150 kfci.
A new plasma oxidization method was introduced into the fabrication process of Co-γFe2O3/NiO thin-film magnetic recording media in order to transform CoO-Fe3O4/NiO films into Co-γFe2O3/NiO films. It was found that remarkably effective oxidization was achieved by utilizing oxygen ions generated in an electron-cyclotron-resonance (ECR) microwave plasma, promoting oxygen generation through the Penning ionization effect using metastable He atoms, and neutralizing samples. In the conventional oxidization method, CoO-Fe3O4/NiO films were heated up to over 300°C, and kept for 1 to 2 hours in air. The new plasma oxidization method shortened the processing time to 10 seconds and lowered the process temperature to 150°C.
To realize higher-frequency recording, a material with a resistivity (ρ) higher than Ni80Fe20 is needed. We thoroughly investigated electroplated Ni80Fe20 films with added Mo to obtain a high-ρ material. We found that MoNiFe films consisting of Mo : 2-3 at%, Ni : 79-80 at%, and Fe : 17-19 at% had good soft magnetic characteristics, high ρ (> 40 μΩcm), and high corrosion resistance. We fabricated a merged-type MR head, using MoNiFe for the upper pole of the write head, and observed the magnetization response at 50 MHz with SKEM. The head showed good magnetization response, which meant that if head higher write efficiency than a Ni80Fe20 head. As a result, we confirmed that MoNiFe films were practical high-ρ pole materials for high-frequency recording.
Non-linear transition shift (NLTS) increases rapidly with an increase in the write frequency. We investigated the relation between the frequency characteristics of NLTS and the write head properties, and proposed a new mechanism whereby high-frequency NLTS depends on the field rise time, not on the spatial field gradient. It is shown that NLTS decreases with an increase in resistivity, a shortening of the yoke length, and an increase in the effective write current. It is also shown that a main factor in NLTS is the write time shift caused by the difference between the first bit and second bit rise times of the write field.
The effect of angular deviation of the exchange bias field on the read performance of spin-valve (SV) heads was investigated. The calculated output voltage showed large variation when the angular deviation of the exchange bias field was increased. For a deviation angle of around 10°, wide variation was observed in the peak asymmetry. This seems to be caused by the generation of magnetic domains in the pinned layer. It is necessary to increase the exchange bias field up 800 Oe in order to diminish the asymmetry instability. Tilting the average direction of the exchange bias field was also effective in suppressing the magnetization reversal in the pinned layer.
The off-track performance of magnetic recording heads is a key issue in achieving high track density. In this study, the position error signal (PES) and off-track capability (OTC) were calculated for spin-valve heads. The position error became large when the direction of the exchange bias field deviated and was disordered in the pinned layer. The OTC also as increased the deviation angle of the disordered direction of the exchange bias field decreased. Therefore, an angular deviation of less than 10 degree is necessary to obtain reliable tracking.
A 3-dimensional micromagnetic model was developed in order to study spin-valve (SV) heads with synthetic ferrimagnetic pinned layers (SF) and SV heads with bias compensation layers (BCL). All of these heads have three-magnetic layers. The magnetization angle change δθ in the free layer caused by the stray field from the medium was calculated for each SV head. When the sensor height is greater than 0.4 μm, δθ for the SV head with BCL is over 20% larger than for the SV head with SF, owing to the magnetic saturation in the BCL. When the sensor height decreases, δθ for the SV head with a BCL decreases because the BCL is not saturated, while δθ for the SV head with SF increases. The output efficiencies of the BCL-type head is almost the same as that of the SF-type head when each sensor height is adequate.
We investigated the relation between the background pressure (PB.G.) of the sputtering chamber and the unidirectional anisotropy field (Hua) of spin-valve films with PdPtMn antiferromagnetic layers fabricated by an ultrahigh vacuum (UHV) sputtering process. Hua increased with decreasing PB.G. until PB.G. reached 2 × 10-7 Pa. The UHV sputtering process helped to reduce the PdPtMn thickness from 25 nm, which was needed in the conventional high-vacuum (HV) sputtering process, to under 15 nm while preserving the magnitude of Hua. We fabricated a spin-valve structure with total thickness of 26.5 nm exhibiting a large MR ratio over 8.0%, sufficient Hua (>500 Oe), and large sheet resistance change (Δρ/ttotal = 1.6 Ω).
Observation of the recording gap field in the high-frequency region is important for developing high-frequency operable recording head. We used Kerr microscopy and MFM for high-frequency observation of recording head. The apparatuses are easy to operate but the data are not quantitative. However, complementary use of these methods provides important information for developing recording heads.
We measured the micro-track profiles of spin-valve heads after damage by ESD. The output was reduced and the profiles showed several peaks depending on the ESD voltage. We proposed two models for the magnetization reversal process of the pinned layer in the spin-valve heads, and calculated the micro-track profiles by using 3D micro-magnetic simulation. In the first model, the pinned layer magnetization is gradually rotated as the ESD voltage is increased. In the second model, the direction of the pinned layer magnetization is reversed in the center of the spin-valve element and the reversal region width is increased as the ESD voltage is increased. The calculation results for the second model agreed fairly well with the experimental results. We think that at first the pinned layer magnetization is locally reversed in the center of the element after ESD in the spin-valve head.
Head-medium interactions (HMI) were estimated by using a finite-element numerical simulation to solve the Poisson equation for the two-dimensional model of a Mn-Zn ferrite ring-type head and a γ-Fe2O3 coating tape system. As a result, it was found that the HMI in the present system with a head-medium spacing of 0.005 μm is equivalent to a 50% increase in output voltage at each bit density. In addition, the output voltage of the conventional method using the reciprocity theorem was found to be about a half of that in the present method.
Two-dimensional read/write simulation based on solution of the Poisson equation was performed on keepered media with a thin soft magnetic layer and a conventional recording one, and a thin-film head system. It was found that the center of the virtual gap created in the read process shifts to the direction opposite to the magnetization direction of the recording layer, and that this shift induces an asymmetrical output waveform. A permeability μ = 100 of the keeper layer was found to reduce the demagnetizing field in the recording layer by 1/2.
The read/write performance of a thin-film single-pole head and a double-layer perpendicular disk was evaluated, including error rate testing. An AMR head with a track width of 1.4 μm was used as a reading head. The channel of the tester was a PR4ML with 8/9 endec. For the testing, readback waveform of the MR head was transformed into a suitable pulse shape with a differentiator for the testing. A D50 of 185 kFRPI and a PW50 of 130 nm were obtained with this equalization. A byte error rate of 10-6 was obtained at 310 kFRPI.
PRML systems for perpendicular magnetic recording using a single-layer medium were studied. Reproduced waveforms at linear densities of 150 to 300 kBPI were acquired by recording and reading-back experiments using a perpendicular single-layer medium, and dibit responses were derived from these waveforms. Using these responses in computer simulation, the performance of PRML systems for (1,7)RLL code was estimated from the SNR required at the reading point to achieve a bit-error rate of 10-4. The results show that a PR(1,2,1,0,-1,-2,-1)ML system has a much better performance than a PR5ML system at linear densities of 250 to 300 kBPI.
Magnetic force microscopy (MFM) has been widely used to investigate magnetized states of recording media, and a method of analyzing MFM images as stochastic signals has been proposed. Through the analysis of the variance computed by this method, a parameter L/W was found. However, the relation between the variance variation and the recorded state of media is not well understood. In this study, in order to determine the relation, MFM-out-put signals are simulated by using the micro-track model, and the variation in the variance around the transition region is considered. The relation between the L/W and some media parameters is investigated by means of the above simulation.
Because of the importance of understanding the physical properties of materials in microscopic systems, there has been a growing interest in ultra-fine particles. To obtain nano-size ferromagnets, we used nano-size Co particles prepared by decomposing dicobalt octacarbonyl [Co2(CO)8 · DCOC] in a polymethyl-methacrylete (PMMA) solution in toluene. The magnetic, magneto-optical, and optical properties of these samples were measured for Co particles ranging from 3.3 nm to 15.9 nm in mean diameter, which were prepared by reducing the solvent/solution ratio. The Faraday spectra of these samples retained a similar wavelength dependence regardless of the size of the Co particles, but the Faraday rotation per magnetic moment increased with decreasing Co particle size. The peak of the optical extinction spectra shifted toward the higher-energy side (blue shift), and a periodic change in the derivative of the extinction spectra appeared for Co particles smaller than 7.8 nm in mean diameter; this may be due to the size effect of the surface plasmon.
The magnetic and magneto-optical properties of TbFeCo/(Pt, Pd, NdCo) multilayer films prepared by sputter-deposition are discussed in conjunction with the multilayer structure. It is most likely that Pt, Pd, and NdCo play a part in increasing the moment of the transition metals in their sub-lattices. The effect of the Pt layers on the polar Kerr spectra is significant at ultraviolet photon energies. A dramatic increase in the magnetic moment and the ωσxy” spectrum for the TbFeCo/Pt multilayer strongly suggest the existence of interfacial FePt alloy layers, and this possibility is supported by a simulation of the Kerr spectra.
A new scheme called MAMMOS for magnetic expansion readout MO is introduced with the aim of achieving high-density recording. A magnetic expansion phenomenon was observed in a magneto-static coupled-type medium with an in-plane magnetization readout layer using dc laser power and a dc magnetic field in the readout process. By taking advantage of this unique expansion phenomenon, it is possible to resolve 0.22 μm domains and to obtain a clear signal in new MAMMOS media.
Recently, many types of magnetically induced super-resolution (MSR) have been proposed for high-density recording on magneto-optical (MO) disks. Among them, double-mask rear-aperture detection (D-RAD) is the most promising, because of its high resolution and crosstalk advantage. However, D-RAD requires a high external magnetic field for MSR readout. I investigated the use of MSR without a readout magnetic field, and made Gd-layer-inserted RAD(Gd-RAD) MO disk. This disk does not need external magnetic field for MSR readout. In recording on a Gd-RAD MO disk with land/groove recording, a C/N of more than 45 dB was achieved for a mark length of 0.3 μm at a track pitch of 0.7 μm.
Magnetic properties of anisotropic M-type Sr-ferrite containing La and Co (Sr1-xLaxCoxFe12-xO19) was investigated in detail. At a composition of x = 0.3, the magnetic properties for permanent magnets were much improved, with the highest values of Br = 4.45 kG, HcJ = 4.82 kOe, and (BH)max = 4.86 MGOe. The temperature dependence of the coercivity was also much improved, with ΔHcJ/HcJ/ΔT = 0.1 %/°C.
The magnetic anisotropy constant K1 and anisotropy field HA of M-type Sr-ferrite containing La and Co (Sr0.7La0.3Fe11.7Co0.3O19) were investigated by the singular-point detection (SPD) method using a pulsed field and SQUID magnetometers, and also by torque measurements. The value of HA=22.2 kOe was obtained by the SPD method at 298 K. The K1 value was 4.2 × 106 erg/cm3 at 298 K, which was determined by extrapolation to the high field of the coefficient of the sin(2 φ) term calculated by Fourier analysis of unsaturated torque curves. This value was 15% larger than that of conventional Sr-ferrite (SrFe12O19) in the temperature range from 77 to 373 K.
The microalloying effect of Cu addition on the microstructure and magnetic properties of Fe3B/Nd2Fe14B nanocomposite permanent magnets has been investigated. With the optimum heat-treatment condition, Cu-containing alloy exhibits a much finer nanocomposite microstructure. Three-dimensional atom probe (3DAP) results have revealed that Cu and Nd form a high density (∼1024m-3) of Cu-Nd clusters containing 5.0 at.% Cu and 7.0 at.% Nd prior to the crystallization reaction of the Nd4.5Fe76.8B18.5Cu0.2 amorphous alloy. These clusters serve as heterogeneous nucleation sites for the Fe3B primary crystals. In the final Fe3B/Nd2Fe14B nanocomposite microstructure, Cu dissolves uniformly in the Nd2Fe14B hard magnetic phase. Improved magnetic properties have been obtained in the Cu-containing alloy; these are attributed to the reduction in the grain size due to the addition of Cu.
Thin films consisting of randomly distributed Nd2Fe14B and α-Fe phases were fabricated on glass substrates by rf sputtering. Although the existence of both Nd2Fe14B and α-Fe phases were confirmed by X-ray diffraction, the magnetization curves showed a single-phase-like behavior. This result indicates exchange coupling between the Nd2Fe14B and Fe phases. On the basis of Rietveld analysis of the X-ray diffraction profiles, the volume fractions of the Nd2Fe14B and Fe phases were estimated. With an increase in the volume fraction of Fe (VFe) from 5% to 76%, Hc decreased from 12.3 to 0.8 kOe, while Mr/Ms increased from 0.54 to 0.83. The mean grain size, which was estimated from the widths of the X-ray diffraction peaks, decreased with increasing VFe. Micromagnetic calculations of magnetization curves suggested that the effective exchange coupling between the soft and hard phases becomes larger with increasing VFe, because of the decreasing grain sizes.
Highly aligned SmFe12/α-Fe nanocomposite thin films were fabricated by rf magnetron sputtering onto heated glass substrates. The volume fraction of the α-Fe phase (VFe) was adjusted systematically by putting a different number of Sm tips (5 × 5 mm2) on the Fe target. Nearly single-phase SmFe12 films of ThMn12-type structure with the (001) plane aligned parallel to the film plane were synthesized at a substrate temperature Ts of 550°C by using 28 Sm tips. These films exhibited good squareness in the demagnetization curve. By reducing the number of Sm tips to 12 and keeping the substrate temperature Ts at 550°C, we fabricated nanocomposite films with different VFe’s. Two different series of film structures with and without Ti underlayers (50 nm) were fabricated, and Ti capping layers (50 nm) were deposited in both series. In films without Ti underlayers, good (001) textures were confirmed by X-ray diffraction and a peak (BH)max of 20 MGOe was obtained for VFe of about 25%. In the series of films with Ti underlayers, coexistence of (001) and (101) textured grains was observed, while a maximum (BH)max of 22 MGOe was obtained for VFe of about 6%.
A device for controlling the temperature of a sample was installed in a high-field magnetometer using pulsed magnetic fields that we developed. The magnetic properties of various permanent magnets, including high-performance magnets, were measured with this system from room temperature to 200°C. The magnetic properties at high temperatures were successfully measured, as well as those at room temperatures.
Exchange-coupled nano-composite melt-spun powder is a nano-structured composite of soft magnetic phases and hard magnetic phases mutually coupled by exchange interaction at the grain boundaries. Its resource balance and oxidizability are better than those of Nd2Fe14B stoichiometric composition melt-spun powder, because it contains a smaller proportion of rare-earth elements such as neodymium. A permanent magnet rotor (SPM: surface permanent magnet /IPM: interior permanent magnet) was developed by directly molding this melt-spun powder with a laminated steel core, and a possible application was found to high-efficiency IPM motors, which use properties to peculiar the nano-composite melt-spun powder.
The micromagnetic structure of the 180° domain wall in submicron-size ferromagnetic Co wires was investigated by means of magnetic force microscopy. The wall width δ (∼μm) observed in Co wire is much larger than that observed in Co films of the same thickness. From micromagnetic calculation using the Landau-Lifshitz-Gilbert (LLG) equation, the magnetic structure of the 180° wall is expected to be a large vortex accompanied by a magnetic ripple structure. This complicated 180° wall is formed to suppress the demagnetizing energy due to a head-on-head configuration of the magnetization, which results in a micron-scale-wide transition area of the wall. The wire-width dependence of the 180° wall width obtained by micromagnetic calculation is almost consistent with that measured from the magnetic force micrograph.
Recently, unique multiple microwave absorption has been observed in ferromagnetic Ni80Fe20 wire arrays with lateral periodicity. As the origin of this phenomenon, we have proposed the excitation of dipolar standing waves arising from a novel collective motion of giant magnetic moments. In the present study, the dependence of the microwave absorption characteristics on the wire spacing, width, and number of wires was investigated to confirm our model. The intensity of the absorption with higher wave number decreased as wire spacing increased. Complex spectra were observed in arrays with wider wires, suggesting an overlap of main and multiple absorption. No change was obtained in the microwave absorption characteristics when the number of wires was varied between 50 and 500. These results imply the validity of the dipolar standing wave model.
The composition dependence of the magnetoresistance, resistivity, magnetization, and crystal structure were investigated for Co2MnAl1-xSix and A2MnAl(A = Fe-Co, Co-Ni) Heusler alloys prepared by the rapid quenching method. The crystal structure of the alloys was B2 structure except for Co2MnSi, which was L21 structure. Both GMR and AMR were observed in several alloys. The GMR exhibited a maximum at x = 0.2 and A = Fe0.1Co0.9. The sign of the AMR was negative in several alloys. The composition dependence of the magnetoresistance, resistivity, and magnetization was calculated by using a simple model taking account of the reported DOS. The composition dependence of GMR and AMR is discussed.
CoxCu100-x binary alloys with Co concentrations of x = 5 - 30 were produced by mechanical alloying. We examined the magnetoresistance (MR) and magnetism in the temperature range from 5 K to 300 K for the as-milled CoxCu100-x alloys, and investigated the relationship between the MR and the magnetization. The MR for the as-milled samples is characterized as follows: (1) For samples with x ≤ 15, the MR ratio increases at low temperature (5.5% at 5 K), and changes in proportion to the square of the magnetization, M2, (2) for a sample with x = 20, the MR ratio measured at temperatures below 120 K shows a constant value (∼3%), and is not proportional to M2 in this temperature range, and (3) for samples with x ≥ 25, the MR ratio decreases with decreasing temperature, and is not proportional to M2. The magnetization measured at high temperature shows superparamagnetic behavior for samples with x ≤ 20, and has a ferromagnetic component for samples with x ≥ 25.
The structures and magnetostrictive properties of TbxDy1-xFe1.9 (x = 0.25, 0.30, 0.35, 0.50, 0.70) alloys prepared by a conventional induction melting and casting method were investigated. These alloys had a columnar structure in the thermal flow direction, and their grain size decreased with increasing Tb content. The magnetic and magnetostrictive properties reflected the magnitude of the magnetocrystalline anisotropy and the saturation magnetostriction. The result is related to the Tb/Dy ratio of alloys. The magnetostriction increased to more than 1500 ppm by annealing, and with decreasing the lattice spacing of the Laves phase. Grain growth was observed simultaneously.
The electrical and magnetic properties, including the magnetoresistance (MR) effect, of Lan-nxCa1+nxMnnO3n+1 thin films (n = ∞, 2; x = 0.3) grown on various substrates were investigated. For n = 2 (La1.4Ca1.6Mn2O7) thin films, the cusp temperature (Tcρ) in the ρ-T curve decreased very sharply with a decrease of the out-of-plane lattice parameter (a). The MR effect was enhanced drastically by decreasing Tcρ. These behaviors are interpreted in relation to the change in the transport character along the c-axis due to the strain.
Spin-unrestricted band calculation for 3d transition metals (atomic number Z=24-28) in bcc and fcc lattices was performed with various lattice parameter. It is shown that magnetic moments generally appear or disappear in all 3d metals investigated when the atomic volume is increased or decreased for bcc and fcc structures. Comparison between the total energy obtained by spin-restricted and spin-unrestricted calculation indicate that there is a region in which non-magnetic state is stable, in spite of the appearance of a ferromagnetic self-consistent solution.
YBa2Co3Oy prepared at 1200 K under reduced pressure forms a cubic perovskite type oxide with a superstructure (a = 1.24 [nm] : E phase). Heat treatments of the E phase oxide in oxygen of 0.106 [MPa] at 1100 [K], 1200 [K], and 1320 [K] formed a tetragonal oxide (a = 1.22 [nm], c = 1.25 [nm] : C phase), an orthorombic oxide (a = 0.389 [nm], b = 0.365 [nm], c = 1.253 [nm] : D phase), and a tetragonal oxide (a = 0.39 [nm], c = 1.13 [nm] : A' phase) with a small amount of other oxides, respectively. The magnetic susceptibilities of the E and C phases oxides are expressed as a sum of a temperature-independent term and the Curie-Weiss term. The D phase oxide is a ferromagnet with magnetization σ = 0.63 μB/Co and Curie temperature Tc = 57 [K]. The A' phase oxide is a paramagnet with anomalous susceptibility maximum at 170 [K]. The electrical resistances of the four oxide phases are semiconductive and, in addition, only the E phase oxide shows a remarkable resistance decrease below 200 [K].
The thermomagnetic behavior of ferromagnetic pseudo-binary compounds Sm1-xRxAl2 (R = Sc, Y, La, Nd, Gd) was studied. For R = Sc, Y, La, the ordering temperature gently decreased in proportion to x, and little change in shape was observed in their thermomagnetic curves. The magnetic substituents Nd and Gd, on the other hand, had a considerable influence on the thermomagnetic properties. Due to the negative contribution of the spin moments to the magnetization in SmAl2 and ferromagnetic coupling between the spins of Sm and the substituent, Nd increased the resultant magnetization and a small amount of Gd decreased it. In the latter case, compensation between the partial magnetization arising from the spin moments and that arising from the orbital ones was observed at 81 K and 64 K for x = 1.8% and 2.6%, respectively.