Vol. 48, No. 13 (1999)
1999-07-05
ATOMIC AND MOLECULAR PHYSICS
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
1999, 48 (13): 8-15.
doi: 10.7498/aps.48.8
Abstract +
[Ni80Fe20/Cu]15 multilayers were fabricated by dc-magnetron sputtering and annealed at 150, 250 and 350℃, respectively. The structures were investigated by low-angle and high-angle X-ray diffraction. It was found that, as the annealing temperature increases, the [111] preferred orientation of superlattices is improved slightly, while the superlattice period, interplane distance, average multilayer coherence length decrease. The interfacial roughness increases with the increase of annealing temperature and/or annealing time, this can be attributed to the Ni80Fe20 and Cu sublayers has been revealed by simulation of high-angle X-ray diffraction, and its thickness increases as the annealing temperature of annealing time increases. The simulation results furthermore showed that the interplane distances of the Ni80Fe20 layer keeps constant, and that the Cu layer decreases slightly as the annealing temperature increases.
1999, 48 (13): 16-21.
doi: 10.7498/aps.48.16.2
Abstract +
The microstructure and magnetic domain structures of the annealed quick-quenched ribbon Sm2Fe14.5Cu0.5Ca2Cx were studied by using magnetic force microscope. The results of the topography image and magnetic force image (MFI) show that the grain size is between 2555nm, whereas the domain size is between 200400nm. The magnetic domain length scale is much larger than the grain size. The domain comprises of a lot of grains, which were called interaction domain. The detail analysis such as power spectral density analysis, the maximum phase shift and roughness analyses on the MFI demonstrated that they are connected with the intrinsic magnetic properties such as HA in some way.
The Texture and Topography of Melt-Spun Ribbons of Nd2Fe14B/α-Fe Two-Phase Permanent Magnetic Alloys
1999, 48 (13): 22-27.
doi: 10.7498/aps.48.22
Abstract +
The texture and topography of melt-spun ribbons of nanocrystalline two-phase permanent magnetic alloys was studied by X-ray diffractometry and scanning probe microscopy. It was found that a pronounced preferred orientation existed in the free-side surface of melt-spun ribbons. Compared with ternary NdFeB alloy, adding Dy+Ga can increase the texture in free-side surface and refine the microstructure and topography of the ribbons.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
1999, 48 (13): 28-34.
doi: 10.7498/aps.48.28
Abstract +
The influence of the different buffer layers on the giant magnetoresistance (GMR) of the Co/Cu/Co sandwich was investigated. It was found that the GMR effect strongly depends on the magnetism of the buffer layer and crystallization of the sandwich induced by the buffer layer. Due to the anti-ferromagnetic coupling between the Cr and Co layer, anti-ferromagnetic Cr layer enlarged the difference of the magnetic behavior between the two Co layers and presented a high GMR value larger than 6%. However, as the coercive force was enlarged also, its magnetic sensitivity could not be high. Ti and Ni buffer layer could form strong (111) texture in the sandwich, which also enlarged the difference between the two Co layers, and achieved GMR values over 5%. Furthermore, the ferromagnetic Ni layer reduced the coercive of the sandwich, and enhanced the sensitivity significantly.
1999, 48 (13): 35-39.
doi: 10.7498/aps.48.35
Abstract +
Abnormal longitudinal magnetoresistance (LMR) in self-doped silver telluride films at low temperature is investigated. In the Ag2.1Te films, we observe the large negative LMR and the multipeaks in magnetic resistivity ρand LMR that strongly depend on doping concentration and temperature. The abnormal MR behavior, which might result from the complex structure and texture of the films, is explained by means of Toyozawa model.
1999, 48 (13): 40-46.
doi: 10.7498/aps.48.40
Abstract +
Bullk materials of two-element-doped manganite La0.67(Ca0.6Ba0.4)0.33MnOz (LCBMO) which were prepared by solid state reaction method, where shown to have cubic polycrystalline structure. The magnetic and colossal magnetoresistive properties of LCBMO were investigated and were compared with those of one-element-doped La0.67Ca0.33MnOz (LCMO) and La0.67Ba0.33MnOz (LBMO)prepared by the similar technique. The results showed that the Curie temperature (TC) of LCBMO was 312K, which was between those of LCMO and LBMO, and that the metal-semiconductor transition temperature (Tp) and magnetoresistance (MR) peak temperature (Tm) of LCBMO under μ0H=0.6T field were 306 and 298K respectively, both of which were close to its TC and were also between the Tp and Tm of LCMO and LBMO. Under μ0H=0.6T applied field, the colossal magnetoresistance value at corresponding Tm was 41% for LCMO, 24.7% for LCBMO, 8% for LBMO, but at room temperature (300K) the MR value of LCBMO still reached 20%, which was greatly larger than those of LCMO and LBMO, i.e.2.0% and 2.4%, respectively. It was observed that at low temperatures far below Tm there still existed magnetoresistance effect in LCMO, and the MR value of LCBMO and LBMO increased with decreasing temperature. These magnetoresistance properties at low temperatures could be ascribed to the intrinsic structural characterstics such as grain boundaries and density.
1999, 48 (13): 47-51.
doi: 10.7498/aps.48.47
Abstract +
The Hall effect in Ni0.8Co0.2-SiO2 granular films which were fabricated by ion beam sputtering technique was studied. The saturated Hall resistivity reached 6.3μΩ·cm in an applied field of 9.5×105 A/m at room temperature when NiCo volume fraction x is near the metal-insulator transition threshold. The temperature dependence of resistivity in these samples with different NiCo compositions was also investigated. It showed-lg T dependence in low x samples, which gradually showed metallic as x increased. Transmission electron microscopy and vibrating sample magnetometer were used to study the microstructures and magnetic properties, the dependence of transport properties on microstructure was also discussed.
1999, 48 (13): 52-55.
doi: 10.7498/aps.48.52
Abstract +
A series of Co35(SiO2)65 (volume fraction) nano-granular films of heat treatment at different annealing temperatures (Ta) were fabricated using ion-beam sputtering technique. The giant magnetoresistance of the samples was found to decrease with increasing annealing temperature. It was found that with increasing annealing temperature to 500K, the magnetic domains of Co35(SiO2)65 nano-granular films were more and more clear, which showed that with increasing annealing temperature, the neighboring isolated Co particles tended to arrange their magnetic moments parallel to each other, thus led to the decrease of the giant magnetoresistance of Co35(SiO2)65 nano-granular films with increasing annealing temperature.
1999, 48 (13): 56-61.
doi: 10.7498/aps.48.56
Abstract +
In this paper, we report the formation and superconductivity of quaternary intermetallic system Yni2B2Cx with ThCr2Si2-type structure. Samples prepared by arc-melting crystallize in single phase of the composition of YNi2B2Cx when x=0.9—1.2 while the secondary unknown phases increase obviously when x＜0.8 or x＞1.2. Superconducting-transition temperature Tc determined by the tem,perature dependence of magnetization displays two steps with increasing carbon concentration: Tc≈12.5K for x≤0.8, Tx≈15K for x≥0.9.
1999, 48 (13): 62-67.
doi: 10.7498/aps.48.62
Abstract +
Morphological alloy of Nd4.5Fe76.3Ga0.3Co1.0B18 prepared by rapid quenching was crystallized to obtain the manocrystalline permanent magnetic materials in which Fe3B were the dominant phases. The X-ray diffraction method, the transmission electron microscopy technique and magnetic measurement were used to analyze the microstructure and magnetic properties of the nanocomposite materials. The relationship of the microstructure, the magnetic properties with the exchange coupling interaction between crystallites was studied by determining the δM curve of the nanocomposite magnets.
1999, 48 (13): 68-73.
doi: 10.7498/aps.48.68
Abstract +
The effect of substituting Mn by Co and Cr on the magnetic properties of layered perovskite manganese oxide La1.2Sr1.8Mn2O7 is investigated. Co doping results in the frustration of long-range ferromagnetic (FM) order, weakening of ferromagnetism, and occurring of cluster-glass and spinglass state, indicating that no double-exchange interaction occurs between Co and Mn ions. However, the long-randge FM order still exists as Mn is replaced by Cr, which verifies that there is FM interaction between Mn3+ and Cr3+.
1999, 48 (13): 74-79.
doi: 10.7498/aps.48.74.2
Abstract +
Structure and magnetic properties of R(Fe1-xNix)11.3Nb0.7 (R=Gd, Tb, Dy, Ho, Er and Y) compounds have been studied by means of X-ray diffraction and magnetic measurements. Substitution of Ni for a fraction of Fe does not change the structure of R Fe11.3Nb0.7, but leads to the contraction of the unit cell volume, the rapidly increasing of the Curie temperature and monotonic decreasing of saturation magnetization. It is notable that introduction of Ni leads to the sharply decline of the easy-axis anisotropy of Fe sublattice and the changes of the spin reorientation temperature Tsr of R Fe11.3Nb0.7 (R=Tb, Dy, Er). A qualitative explanation of the relationship of Tsr and Ni content is given based on the theory of crystal field.
1999, 48 (13): 80-86.
doi: 10.7498/aps.48.80
Abstract +
The structural and magnetic properties of synthetic Gd3(Fe1-xCox)25Cr4(0≤x≤0.6) and Gd3Fe29-yCry(3.5≤y≤5.0) compounds have been investigated. The structures of all the compounds are found to belong to the A2/m space group. Increase of Cr content leads to decreasing Curie temperature, decreasing saturation magnetization and decreasing anisotropy. Substitution of Co for Fe leads to a clear contraction of the unit-cell volume, but the increase of Curie temperature. Composition dependence of saturation magnetization at 5K reaches a maximum around x=0.3. It is noteworthy that substitution of Co for Fe results in a significant change of magnetocrystalline anisotropy of the Co sublattice, and changes of the easy magnetization direction of Gd3(Fe1-xCox)25Cr4 compounds from basal plane to easy axis.
1999, 48 (13): 87-92.
doi: 10.7498/aps.48.87
Abstract +
Magnetic properties of RCo10Mo2(R=Y,Ho) compounds have been studied. One-sublattice and two-sublattice models have been used to explain the magnetic process of aligned samples of YCo10Mo2 and HoCo10Mo2 compounds, respectively. Anisotropy properties and exchange interaction of the Ho and Co sublattices have been studied.
1999, 48 (13): 93-97.
doi: 10.7498/aps.48.93
Abstract +
The isotropic Pr-doped SrFe12O19 powders have been synthesized by mechanical milling and subsequent hear treatment. The effects of Pr3+ doping concentration and annealing condition on the microstructure and magnetic properties have been systematically investigated. It is found that the Pr3+ doping results in the increase of the temperature for the formation of hard magnetic compounds. The Curie temperature of PrxSr1-xFe12O19 samples keeps constant with the variation of composition of the sample; however, it decreases slightly with the increase of annealing temperature. The addition of a small amount of Pr3+ in the samples is beneficial to the improvement of coercivity, but accompanying with the deterioration of magnetization. The effect of annealing temperature on magnetic properties is different for the samples with different compositions.
1999, 48 (13): 98-104.
doi: 10.7498/aps.48.98
Abstract +
The general dispersion relation of width mode of the magneto-static surface wave (MSSW) propagating in YIG multilayer films with finite sample width and arbitrary parameters is established. The theory includes all the situations of MSSW dispersion control by multilayer films and is in a better agreement with the actual situation. The dispersion of MSSW width mode in [(YIG/GGG)10/metal] periodic multilayer films were numerically investigated by applying the theory. Numerical results showed that the main working mode of MSSW propagating in multilayer YIG films is the first order width mode, the dispersion of MSSW can be controlled efficiently by the multilayer periods and the parameters of each layer. It also is influenced by the sample width.
Doping Effects Arising From the Substitution of Ti for Mn in the Perovskite Compounds La2/3Ca1/3MnO3
1999, 48 (13): 105-110.
doi: 10.7498/aps.48.105
Abstract +
The magnetic and transport properties of compounds La2/3Ca1/3Mn1-xTixO3(0x0.3) have been investigated. The substitution of Ti for Mn suppresses the ferromagnetism and metal conduction and increases magnetoresistance dramatically. In the case of low doping (x0.04), substituting Ti for 1% Mn lowers Curie temperature TC and metal-insulator transition temperature Tp by about 31 and 26.5K respectively. The magnetic spontaneous state becomes cluster glass state for the compound with x=0.06, and turns into spin-glass state for the compound with x=0.20. The magnetic dilution and the local lattice distortion due to the introduction of Ti are suggested to explain the experimental results.
1999, 48 (13): 111-115.
doi: 10.7498/aps.48.111
Abstract +
Arrays of nickel nanowires are fabricated by electrochemical deposition into template-Anopor. The wires have high aspect ratio L/D=250, with diameter 200nm and length 50m. The easy axis is perpendicular to the nanowire because of the static magnetic interaction between the neighbouring nanowires.
1999, 48 (13): 116-120.
doi: 10.7498/aps.48.116
Abstract +
A series of Gd3Al2-xGax alloys over a composition range (x=0,0.1,0.3,0.5) were prepared from high purity Gd, Al, and Ga by arc melting under purified argon atmosphere on a water-cooled copper crucible, then annealed in vacuum at 1073 or 1173K for 36h. The X-ray diffraction pattern indicated that these alloys were single phase of Zr3Al2-type structure. Magnetization isotherms at different tempertures of these alloys were measured between 180 and 300K under the magnetic field up to 1.12106A/m using vibrating sample magnetometer. We found that magnetic entropy change of Gd3Al2-xGax(x=0.1,0.3,0.5) was larger than that of Gd3Al2, and the s of change (about 3.0J/kgK) of Gd3Al2-xGax(x=0.1) was observed at 280K under a magnetic field of 1.12106A/m.
1999, 48 (13): 126-131.
doi: 10.7498/aps.48.126
Abstract +
The magnetization curves of gadolinium were measured with a vibrating sample magnetometer, from which the function M(H,T) was obtained using two-step least square fitting. Then magnetic entropy changes can be calculated. These works can provide the perliminary information needed for the design of magnetic refrigerator.
1999, 48 (13): 132-137.
doi: 10.7498/aps.48.132
Abstract +
In the ranges of f=1020000Hz and Bm=0.11.0T, the core loss has been measured for nanocrystalline Fe73.5Cu1Nb3Si13.5B9 alloy with high Br. The total power loss was decomposed into the sum of the classical eddy current loss, the hysteresis loss and the excess loss. The results show that the change of the total loss per cycle with frequency clearly shows a nonlinear behavior, which has been described in terms of Bertotti's statistical theory of loss. The frequency range examined can nearly be divided into two intervals, in which there exist two different describing ways.
1999, 48 (13): 138-143.
doi: 10.7498/aps.48.138
Abstract +
Based on Maxwell equations, the theoretical formulas of microwave electromagnetic parameters of polycrystalline iron fiber absorber are dervied. The anisotropy of microwave electromagnetic parameters of polycrystalline iron fiber absorber is explained by use of numerical calculations. Some samples of fiber orientation have been produced and their electromagnetic parameters have been tested, the results confirm the anisotropy of electromagnetic parameters. Both of the theoretical and experimental results demonstrate that the axial permeability of polycrystalline iron fiber is greater than its radial permeability, and the axial permittivity of polycrystalline iron filber is greater than its radial permittivity.
1999, 48 (13): 144-150.
doi: 10.7498/aps.48.144
Abstract +
The giant magnetoriesistance (GMR) effects in sandwiched Co/Cu/Co and Co/CuMn/Co structures have been investigated. The GMR oscillates with the spacer thickness for both cases, but nearly antiphased. With diluted Mn atoms in the Cu spacer, the GMR curve as a function of the magnetic field changes a lot, and the saturation/switching field for GMR can be reduced greatly compared with that in Co/Cu/Co systems. This may suggest one way to obtain a highly sensitive GMR.
1999, 48 (13): 151-158.
doi: 10.7498/aps.48.151
Abstract +
A series of Pt/Co/Pt/Ni modulated multilayer with Ni layer thickness tNi ranging from 0 to 2.4nm have been prepared by magnetron sputtering on Pt buffer. The relations between conductivity tensors σ1xx,σ2xx,σ1xy,σ2xy and tNi were calculated with measured values of Kerr rotation, ellipticity, refractive index and absorption index. And then, θK =θK [σ1xx(tNi,σ2xx(tNi),σ1xy(tNi),σ2xy(tNi)] as a compound function of tNi was calculated. It exhibits that, with the change of tNi, σ2xy is the major factor to influnce θK at short wave length and all of the four conductivity tensors are important at long wavelength, no one is negligible. We think that the splitting of Pt 5d band, which originates from spin-orbit coupling, decreases with the increase of tNi. The Curie temperature TC decreases monotonically with increasing tNi. For purpose of application, we show a range of tNi (0.3—1.0nm), in which TC is lower while θK and R is higher than pure Pt/Co multilayers.
1999, 48 (13): 159-163.
doi: 10.7498/aps.48.159
Abstract +
The influence of current annealing process on the giant magneto-impedance (GMI) effect of Fe84Zr8Nb3.5Cu1 ribbons was studied. The obtained results showed that with increasing annealing current, the GMI ratio ΔZ/Z(ΔZ/Z=(Z(H)-Z(Hmax))/Z(Hmax)) is enhanced. The maximal GMI ratio of about 62% is obtained for the sample annealed at 820 mA for 10min, while the sensitivity can reach a value up to about 0.23% (A/m)-1. In combination with the evolution of electrical and soft magnetic properties, the dependence of the GMI effect on the frequency and applied longitudinal field has been discussed by means of skin effect.
1999, 48 (13): 164-168.
doi: 10.7498/aps.48.164
Abstract +
The melt-spun ribbons of Nd8Fe85Mo1B6 have been prepared by directly rapid quenching at different wheel speeds. From the result of vibrating sample magnetometer measurement, we found that the magnetic properties of the ribbons are dependent on the wheel speed. X-ray diffraction and thermomagnetic analysis were also used to investigate microstructure and phase composition of the samples. The result shows that the TbCu7 phase increases with increasing wheel speed; at the same time, a decreased grain size of the α-Fe phase is observed. The change of magnetic properties is due to the change of phase composition and grain size of the samples.
1999, 48 (13): 169-174.
doi: 10.7498/aps.48.169
Abstract +
In this paper we use a bond-operator mean-field theory to study the quantum phase transition in the bilayer Heisenberg antiferromagnet. The obtained critical point and low temperature quantum critical behavior are consistent with the numerical results and the nonlinear σ model results. In the very low temperature (T≤0.3J1, J1 is the in-plane antiferromagnetic coupling), where the numerical results are not available, present paper gives new evidence for the quantum critical behavior.
1999, 48 (13): 175-179.
doi: 10.7498/aps.48.175
Abstract +
The giant magneto-impedance (GMI) effects in amorphous Co70Fe4.5Ni4Nb1Si12.5B8 alloy ribbon have been observed. It is shown that the GMI effects increase with driving current frequency and an appropriate annealing can enhance the effect. A large MI ratio of about 120% in the as-cast sample and a ratio of about 400% in a suitably annealed sample have been measured at 5MHz.
1999, 48 (13): 180-186.
doi: 10.7498/aps.48.180.2
Abstract +
The dependence of reduced remanence (Mr/Ms) and coercivity of Sm22Co78/Fe65Co35 bilayer and Sm22Co78/Fe65Co35/Sm22Co78 triple-layer films on Fe65Co35 soft-magnetic layer thickness d, was systematically investigated. All the hysteresis loops of the films exhibited a single-phase behavior, reflecting a strong exchange coupling between soft-and hard-magnetic phase. Mr/Ms showed a monotonic increase with increasing Fe65Co35 thickness d, and the coercivity would show a peak with increasing d. From the plot of M versus applied field H, it is shown that the positive profile decreases and the negative interaction profile increases with the increase of interfaces between soft-and hard-layers.
1999, 48 (13): 187-192.
doi: 10.7498/aps.48.187
Abstract +
Magnetic properties and giant magneto-impedance (GMI) effects of Fe73.5Cu1Nb3Si13.5B9 single layered films and sandwiched fimls using Cu or Ag as the central layer prepared by radio frequency sputtering are investigated. The as-deposited single layered films are in amorphous state. The domain structures of single layered films annealed as 380℃ show that the films are in nanocrystalline state with homogeneous magnetization. The samples possess excellent soft magnetic properties and have the maxiumum values of GMI effects, the maxiumum GMI ratios are 18% and 14% in longitudinal and transverse fields, respectively, at 13MHz. Sandwiched films in the as-deposited state possess large GMI effects, the maximum GMI ratios of sandwiched films with a Cu central layer are 32% and 11% for longitudinal and transverse cases, respectively, and those of sandwiched films with a Ag central layer are 47% and 57% for longitudinal and transverse cases, respectively. Sandwiched films using Cu as the inner layer annealed at 250℃ exhibit large magneto-inductance effect at low frequencies. The maximum magneto-inductance ratio is 1733% at 100kHz.
1999, 48 (13): 193-199.
doi: 10.7498/aps.48.193.2
Abstract +
Amorphous Fe78Si9B13 and (FeNiCr)78 (SiB)22 ribbons and their composite ribbons were made by a double-chamber-crucible technique. Ms-T curves and hysteresis loops of the lap-wound-cores of the two ribbons and composite ribbons were measured. The hysteresis loop of the lap-wound-cores was waist-like, and was closed but not equal to the average of the two components. For the composite ribbon cores, their Ms-T curve was practically the average of the two components. However, their hysteresis loop was no longer waist-like, but a flat one. These changes of the hysteresis loops of the lap-wound-cores and composite cores were suggested to result from the internal stress induced by the difference of the thermal expansion and magneto-striction of the two components.
1999, 48 (13): 200-203.
doi: 10.7498/aps.48.200
Abstract +
In Py/CrAl bilayers (where Py=Ni81Fe19), the coercivity at room temperature is found to be a linear function of 1/t3/2FM, indicating the existence of random exchange interaction at the FM/AFM interface (FM=ferromagnetic, AFM=antiferromagnetic). The AFM layer thickness dependencies of the He and Hc are also studied.
1999, 48 (13): 204-210.
doi: 10.7498/aps.48.204
Abstract +
The temperature dependence of demagnetization curve, intrinsic coercivity and magnetic viscosity has been measured on single crystal Dy (Fe0.8Al0.2)2 in [100], [110] and [111] directions. The staircase and a large jump of demagnetization curve, an obvious peak of coercivity vs temperature, and the magnetic viscosity being independent of the temperature etc., were observed. The observed features were analyzed within the theory of the macroscopic quantum effects for domain walls tunneling in the single crystal. A crossover temperature has been observed at Tcr=5.5K between classical thermal activation and quantum tunneling regimes.
1999, 48 (13): 211-216.
doi: 10.7498/aps.48.211
Abstract +
Nanocomposite Nd3.6Pr5.4Fe83Co3B5 ribbons were prepared by direct melt spining at wheel speed of 20m/s. Although Nd2Fe14B-type phase and α-Fe were found in the ribbons, a single hard magnetic behavior with high coercivity can only be found in the hysteresis loop. The recoil curves show a comparatively high degree of reversibility in the fields below coercivity. From the investigations of reversible and irreversible portions in DC demagnetization remanence curve, the irreversible nucleation field of about 440 kA/m has been obtained in melt-spun Nd3.6Pr5.4Fe83Co3B5 ribbons. The measurements of magnetic viscosity show that the time-dependent magnetization changes are associated with reversal of the hard phase. The thermal fluctuation field of about 2.0kA/m was obtained.
1999, 48 (13): 217-223.
doi: 10.7498/aps.48.217
Abstract +
The ratio of non-magnetic to magnetic atoms was adjusted from 3:1 to 1:1 within the (Pt3Co)1-xNix system by sticking Ni chips to the Pt3Co target. X-ray diffraction and magnetic results showed that perpendicular magnetic anisotropy was not caused by texture at least in the Ni content range of 0.33—0.50. Furthermore, the effect of the Ni addition to the CoPt3 alloy films on their magnetic and magneto-optical propertical were investigated. The result shows that satisfactory Curie temperature TC, cohercivity Hc and Kerr rotation can be simultaneously obtained by selecting suitable Ni content (x=0.43) in the (Pt3Co)1-xNix system. This work provides an experimental basis for the application of PtCoNi alloy films.
1999, 48 (13): 224-229.
doi: 10.7498/aps.48.224
Abstract +
The Tb0.17Co0.83/Si multilayers prepared by a rf magnetron sputtering system with different Si thickness have been investigated. X-ray diffraction, magnetic measurement and Kerr rotation have been performed. With increasing thickness of Si layer tSi, the perpendicular anisotropy constant Ku decreased rapidly. The saturation magnetization Ms and the Kerr rotation θK decreased linearly when tSi increased. It was assumed that Co2Si and Tb had been formed in the interfacial zone between TbCo and Si layers. The reduction of Ku, Ms and θK is attributed to the decrease of the effective thickness of magnetic layer, which is linear with tSi.
1999, 48 (13): 230-235.
doi: 10.7498/aps.48.230
Abstract +
Pure, single-phase La0.7Ca0.3MnO3 perovskites with giant magnetoresistance effect have been successfully prepared by mechanical alloying. The amorphous phase formed in milled smples transforms at about 920K into perovskite-type phase. Following the law of mass action, crystallization dynamics of the amorphous phase has been discussed. The activation energy for crystallization transformation is calculated to be about 265kJ/mol. The characterization of resistivity ρ(T) for La0.7Ca0.3MnO3 perovskites has also been investigated. At low temperatures T, ρ(T) has a directproportion dependence on T2. With increasing annealing temperature, the slope of ρ-T2 curve decreases. The temperature dependent magnetoresistance effect at temperatures far below the Curie temperature can be well expressed by the equation Δρ/ρ0=p1-p2T3/2-p3T5/2.
1999, 48 (13): 236-243.
doi: 10.7498/aps.48.236
Abstract +
With plasma oxidization to create an insulating layer of Al2O3, we have repeatedly fabricated some Ni80Fe20/Al2O3/Co magnetic tunnel junctions (MTJ), which show obvious tunneling magnetoresistance (TMR) effect. The insulating layer is well formed by the oxidization procedure, which is verified by optical spectra and other measurement results. At room temperature, the maximum TMR ratio reaches 6.0%. The switch field can be less than 800A/m and the relative step width is about 2400A/m. The junction resistance Rj changes from hundreds of ohms to hundreds of kilohms and TMR ratio decreases monotonously with the increase of applied junction voltage bias (under zero magnetic field).
1999, 48 (13): 244-249.
doi: 10.7498/aps.48.244
Abstract +
Pd1-xFex/Fe multilayers (MLs) with x=0,0.34,0.056,0.071 have been prepared by magnetron sputtering. The measurement of saturation magnetization in Pd/Fe MLs in the range of Pd thickness from 4to 18 ML shiows that the interlayer couplings are ferromagnetic and Ms possesses a long-range oscillation with a period of 4 ML Pd. The oscillation phase and period in Pd0.966Fe0.034/Fe and Pd0.944Fe0.056/Fe multilayers remain unchanged as compared with their reference Pd/Fe multilayers. A discussion is given about discrepancy between theory and experiments, concerning with whether a negative polarization of Pd in inner spacer and a long-range ferromagnetic oscillation appears in Pd/Fe systems.
1999, 48 (13): 250-256.
doi: 10.7498/aps.48.250.2
Abstract +
A low-bias-field method was proposed to form single multi-branched domains (MBDs) in garnet bubble films. The formation of MBDs is related to the nucleation of vertical Bloch lines (VBL) in their domain walls. With the decrease of the static bias-field Hb from the critical static bias field for multi-branched expansion H[d], the corresponding MBDs formed become more and more complex, accompanying the appearance of several kinds of hard domains. The fractal geometry was introduced into the study of MBDs. THe curved and branched patterns patterns of MBDs have been quantitatively described by the line-measuring dimension Dline, which is associated with the nucleation of VBL in their domain walls.
1999, 48 (13): 257-262.
doi: 10.7498/aps.48.257.2
Abstract +
Magnetostriction of TbyDy1-x(Fe1-xTx)2(T=Al,Mn) single crystals, prepared by the MCGS-3 CZ instrument, was investigated. The intrinsic magnetostrictive properties were derived by fitting method of X-ray diffraction patterns of polycrystal samples prepared by arc-melting method. The substitution of AL, Mn for Fe lowers the saturation field and magnetocrystalline anisotropic energy. The intrinsic magnetostriction, 111, decreases with increasing amount of Al or Mn. For Tb0.5Dy0.5(Fe0.9Mn0.1)2 single crystals,a large magnetostriction and high d33 can be obtained under the compressive stress of 1226 MPa.
1999, 48 (13): 263-267.
doi: 10.7498/aps.48.263
Abstract +
A series of bulk (La1-xPrx)2/3Sr1/3MnO3 polycrystaline samples were prepared by sol-gel technique and the electrical, magnetic properties and magnetostriction effect were studied. At low temperatures, the magnetostriction was mainly about linear magnetostriction and saturated at low magnetic field, and the saturation field decreased with decreasing Pr content. At x=0.3, we found maximum value of -90×10-6.
1999, 48 (13): 268-273.
doi: 10.7498/aps.48.268
Abstract +
A series of polycrystaline bulk (La1-xRx)2/3Sr1/3MnO3(R=Sm,Tb) over a wide composition range were prepared by two different techniques, and their structure nd magnetostriction effect were studied carefully at room temperature. The X-ray diffraction pattern indicated that the structure of samples transformed from rhombohedral type to orthorhombic phase with decreasing R contents. The sample, composition near the transformation point, had the maximum value of magnetostriction. The magnetostriction may come from the exchange magnetostriction in the samples at room temperature.
1999, 48 (13): 274-279.
doi: 10.7498/aps.48.274
Abstract +
Pr(Fe1-xCox)2 ribbons have been prepared by melt-spinning method. Their structure, magnetic properties and thermal stability are investigated. It is found that Pr(Fe,Co)2 cubic Laves phase can form only when x≥0.2 at wheel speed of 45m/s. For Pr(Fe0.6Co0.4)2 alloy, at wheel speed of 30m/s, the ribbon consistes of a mixture of Pr2(Fe,Co)17, Pr(Fe,Co)2 and rare earth-rich phase. Almost Pr(Fe0.6Co0.4)2 compound a small amount of amorphous phase is observed at wheel speed up to 45m/s. Pr(Fe0.6Co0.4)2 compound becomes unstable above 770℃. The resub-bonded Pr(Fe0.6Co0.4)2 nanocrystalline compound which is obtained at wheel speed of 40m/s combines high magnetostriction (λ∥-λ⊥=140×10-6), with significant magnetic coercivity, iHc=398kA/m.
1999, 48 (13): 280-285.
doi: 10.7498/aps.48.280
Abstract +
A series of polycrystaline bulk samples of (La1-yTby)0.67Sr0.33MnO3(y=0,0.05,0.15,0.20,0.25,0.33,0.40,0.50,0.60,1.00) have been prepared by solid-phase reaction sintering. X-ray diffraction patterns show that the rhombohedral structure has been transfered into orthorhombic structure with increasing Tb content y. For the sample with y=0.40, a colossal magnetoresistance up to 900% has been observed at 180K. When μ0H=1.7T, the anisotropic magnetostriction (λt) of -50×10-6 and volume magnetostriction (ω) -130×10-6 have been observed for the samples of y=0.20 at room temperature, and y=0.33 at 210K respectively.
1999, 48 (13): 286-290.
doi: 10.7498/aps.48.286
Abstract +
The characteristics of magnetostatic forward volume waves (MSFVWs) propagating in magneto-optical (MO) film waveguide under inclined bias magnetic field are analyaed. The dependences of MSFVW propagation constant and dynamic magnetization related to the MO coupling coefficients on mode number, frequency and inclined bias magnetic field are calculated in detail. It is shown that the greater the MSFVW frequency f and the mode number m as well as the less bias magnetic field Hi and inclination θ, the greater MSFVW propagation constant Ks is; the amplitude of zero-mode MSFVWs is much greater than that of high-mode MSFVWs. In an appropriate frequency range, MSFVW amplitude can be increased under an inclined bias magnetic field, and then the diffraction efficiency of guided optical waves with MSFVWs is improved.
1999, 48 (13): 291-297.
doi: 10.7498/aps.48.291
Abstract +
The spin wave manifold (spin wave eigenfrequencies) for grain-surface-layers is obtained from the precession equation in consideration of the existence of impurity-induced and stran-induced uniaxial anisotropy field Hs. The top and bottom of the manifold for grain-surface-layers at various applied fields H are illustrated in comparison with the manifold for the grain-interior-region. With the detalled calculation, it is revealed that the off-resonance effective linewidth ΔHeff arises from the spin wave resonance excited in some grain-surface-layers and is propotional to the volume fraction of grain-surface-layers. Thus a lot of previous experiments on ΔHeff vs grain size and porosity can be understood well, and the physical meaning of ΔHeff is clarified.
1999, 48 (13): 298-303.
doi: 10.7498/aps.48.298
Abstract +
The Kerr rotation of MnBixAl0.15(0.4≤x≤0.9) thin films with and Al protective layer as a function of the Bi concentration, x, has been investigated. Compared with MnBix thin films, it is found that a large enhancement of Kerr rotation appears in the MnBixAl0.15 thin films with 0.4≤x≤0.7, but no enhancement of Kerr rotation appears when x is greater than 0.7. When x=0.5, a maximum Kerr rotation of 2.75° is observed at 633nm for the MnBi0.5Al0.15 thin film, which is much larger than that of 1.56° for the MnBi0.5 thin film. For the MnBixAl0.15 thin films with 0.4≤x≤0.7, the c lattice shrinking may result in a stronger hybridization between Bi 6p and Mn 3d states, which also should be responsible for the large enhancement of Kerr rotatio. In addition, the saturation magnetization Ms is reduced from 4×105A/m for the MnBi0.5 thin film to 3×105A/m for the MnBi0.5Al0.15 thin film, suggesting that some of Al may also substitute for Mn at the octahedrtal sites.
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
1999, 48 (13): 304-308.
doi: 10.7498/aps.48.304
Abstract +
We report a previously undescribed magnetic coccus, designated NMC-1, that was present in surface sediments collected from the pool in Nanjing suburbs. They orientated and navigated along geomagnetic field lines. Transmission electron microscope photographs showed that the NMC-1 contained over ten magnetosomes. The individual mature crystal was 70nm in length and 40nm in width, which were within the calculted stability field for single-domain magnetite. The energy profile of X-rays was collected after electron excitation of the magnetosomes within a single cell. Iron was the predominant detectable element in the particles. Electron diffraction pattern indicated the magnetosomes are single crystals.
