Showing papers on "Magnetization published in 1987"
01 Oct 1987-Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms
TL;DR: In this article, the evaluation of magnetic hyperfine field distributions from 57Fe Mossbauer spectra in systems with both magnetic dipole and electric quadrupole interactions is considered.
Abstract: The evaluation of magnetic hyperfine field distributions from 57Fe Mossbauer spectra in systems with both magnetic dipole and electric quadrupole interactions is considered. This problem is treated in higher order perturbation theory, and the case of general magnetic texture and isotropic electric quadrupole texture is treated in full. Simple expressions are given enabling the calculation of all spectrum line positions, intensities and widths. It is shown that in cases where first order perturbation treatments yield low-field artifacts in the magnetic hyperfine distribution, this procedure yields much more reliable results. It is also shown that the calculated magnetic spin texture is much more reliable. The asymmetry effects from the electric quadrupole interaction and from a correlation between this and a dipole magnetic field are considered.
410 citations
TL;DR: Ferromagnetic resonance data indicate that the two inplane 〈110〉 directions are inequivalent and, together with magnetometry data, show that the average film magnetization decreases as the thickness decreases.
Abstract: Single‐crystal (100)Fe films 90–330 A thick have been grown on etch‐annealed (100)GaAs substrates by molecular‐beam‐epitaxy techniques. Ferromagnetic resonance data indicate that the two in‐plane 〈110〉 directions are inequivalent and, together with magnetometry data, show that the average film magnetization decreases as the thickness decreases. The inequivalence is attributed to the nature of the interface bonding at a (100) zinc‐blende surface. The decreased magnetization is attributed to the formation of Fe2As microclusters in the film due to As diffusion which is supported by Auger and electron diffraction studies. In general, the Fe films grown to date on etch‐annealed (100)GaAs substrates are significantly inferior to those grown on (110)GaAs.
336 citations
TL;DR: In this paper, a new method was used to produce uniaxially aligned small single crystals of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-//sub delta.
Abstract: A new method has been used to produce uniaxially aligned small single crystals of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-//sub delta/. The superconducting critical current deduced from magnetization data is strongly field dependent and highly anisotropic. In the basal plane at T = 4.2 K we estimate that the critical current at zero field is in excess of 10/sup 7/ A/cm/sup 2/.
324 citations
TL;DR: In this paper, extensive magnetization and magnetoresistivity experiments on CeRu2Si2 are described, with special emphasis on the metamagnetic-like transition that occurs atH*=80 kOe.
Abstract: Extensive magnetization and magnetoresistivity experiments on CeRu2Si2 are described, with special emphasis on the metamagnetic-like transition that occurs atH*=80 kOe. By contrast to the low-field susceptibility, the differential susceptibility atH* almost diverges atT→0. It is suggested that high magnetic fields (H>H*) restore a situation where the interactions between particles have collapsed. Comparison is made with other well-known examples: TiBe2, UPt3, TmSe, and3He.
301 citations
TL;DR: In this paper, the magnetic anisotropy of both types of thin films can be interpreted by assuming an interface contribution which favours a perpendicular magnetization, and a volume contribution that favours an in-plane magnetization.
298 citations
TL;DR: In small external fields such double layers order antiparallel with their magnetization perpendicular to the external field in analogy to the spin‐flop phase of antiferromagnets, revealed by the behavior of the static magnetization of such samples as a function of external field and the spectrum of spin‐wave modes with the wave vector parallel to a small external field.
Abstract: Double layers of (100)‐oriented Fe with an individual thickness of ≊100 A, separated by interlayers of Cr or Au with variable thickness were grown epitaxially on Au (100) surfaces. The spin‐wave mode spectra of these double layers as detected by means of light scattering were used to measure the effective exchange coupling of the Fe films across the interlayer. For Au interlayers it decreases monotonically with increasing Au thickness dAu and disappears at dAu≳20 A. For Cr interlayers of proper thickness dCr, i.e., 4 A≲dCr≲9 A we obtain antiferromagnetic coupling of the Fe layers. In small external fields such double layers order antiparallel with their magnetization perpendicular to the external field in analogy to the spin‐flop phase of antiferromagnets. This is revealed by the behavior of the static magnetization of such samples as a function of external field and the spectrum of spin‐wave modes with the wave vector parallel to a small external field.
265 citations
TL;DR: In this article, the magnetic depth profiles near the surfaces of ferromagnets and superconductors were determined by measuring the spin-dependent reflectivities of a well-collimated (0.01°) beam of cold neutrons from surfaces of a few cm2.
Abstract: A description is given of the prototype polarized neutron reflectometer installed at the intense pulsed neutron source. This instrument is designed for determining the magnetic depth profiles near the surfaces of ferromagnets and superconductors, by measuring the spin‐dependent reflectivities of a well‐collimated (0.01°) beam of cold neutrons from surfaces of a few cm2. Magnetic profiles can be determined with the spatial resolution of 40 A, over thicknesses up to 5000 A. Variations of the magnetic flux of the order of 10−5 G cm2 can be detected.
223 citations
TL;DR: Pd/Co and Pd/Fe multilayer films containing ultrathin Co and Fe layers were prepared by vapor deposition on substrates at room temperature and their modulated structure was proved by x-ray diffraction and transmission electron microscopy as discussed by the authors.
Abstract: Pd/Co and Pd/Fe multilayer films containing ultrathin Co and Fe layers were prepared by vapor deposition on substrates at room temperature. Their modulated structure, even for films containing 2‐A‐thin Co and Fe layers, was proved by x‐ray diffraction and transmission electron microscopy. Below a Co layer thickness of about 8 A, the Pd/Co multilayers acquire an easy magnetic axis perpendicular to the film, which is mainly caused by magnetic interface anisotropy. This leads for multilayers containing Co monolayers to almost rectangular hysteresis loops, by which these films may be very suitable as a perpendicular magnetic recording medium. Pd/Fe multilayers also have a perpendicular interface anisotropy, but the shape anisotropy dominates. Per unit Co volume the Pd/Co multilayers have a higher saturation magnetization than pure Co, which is attributed to an induced ferromagnetism on Pd interfacial atoms.
221 citations
TL;DR: Results for layer thicknesses indicate that the magnetization of bilayers of Fe should be perpendicular to the film, and a rapid increase in the Gilbert damping coefficient with decreasing film thickness reflects an enhanced role of spin-orbit coupling.
Abstract: Studies of ferromagnetic resonance lines at \ensuremath{\simeq}73 and \ensuremath{\simeq}36 GHz yield the static and dynamic parameters of ultrathin layers of bcc Fe(100) grown on fcc Ag(100) substrates and covered by fcc Au(100). Results for layer thicknesses of 28, 17, 5, and 3 monolayers when extrapolated to 2 monolayers indicate that the magnetization of bilayers of Fe should be perpendicular to the film. This indicates a large unexplained contribution to the magnetic anisotropy at or near the surfaces. A rapid increase in the Gilbert damping coefficient with decreasing film thickness reflects an enhanced role of spin-orbit coupling.
219 citations
TL;DR: The physical principles relevant to magnetometry are presented and models for intracellular particle motion driven by thermal, elastic, or cellular forces are suggested and described.
181 citations
TL;DR: Epitaxial bcc Fe films grown on Ag(001) are ferromagnetic, and films consisting of more than 5 monolayers have a Curie temperature equal to that of bulk bCC Fe.
Abstract: Epitaxial bcc Fe films grown on Ag(001) are ferromagnetic. At $T=30$ K, the 3- to 4-monolayer films are perpendicularly magnetized at remanence, whereas thinner and thicker films have their magnetization in plane. Above $T=100$ K no perpendicular remanence has been observed for any film thickness. Films consisting of more than 5 monolayers have a Curie temperature equal to that of bulk bcc Fe.
TL;DR: In this paper, a model for the mechanism of magnetization reversal in thin films of amorphous alloys with perpendicular magnetic anisotropy was proposed, which exhibits the observed behavior of the media such as nucleation and growth of reverse magnetized domains under external magnetic fields.
Abstract: A model is proposed for the mechanism of magnetization reversal in thin films of amorphous alloys with perpendicular magnetic anisotropy. Examples of these alloys are TbFe, GdCo, DyFe, and GdTbFeCo, which are currently under investigation as storage media for erasable optical recording applications. The model exhibits the observed behavior of the media such as nucleation and growth of reverse‐magnetized domains under external magnetic fields; square hysteresis loops; temperature dependence of coercivity; formation and stability of domains under conditions of thermomagnetic recording; and incomplete erasure with insufficient applied fields.
TL;DR: Isothermal magnetization curves for the compounds LaFe, PrFe, NdFe and P12 below 6 K reveal a spin-flop or metamagnetic transition.
Abstract: The low-temperature properties of M${\mathrm{Fe}}_{4}$${\mathrm{P}}_{12}$ (M=La, Pr, Nd, and Th) single crystals have been studied by means of electrical-resistivity, magnetization, specific-heat, and magnetoresistivity measurements. Superconductivity among these compounds is known to occur only in ${\mathrm{LaFe}}_{4}$${\mathrm{P}}_{12}$, which has a superconducting transition temperature ${T}_{c}$ of \ensuremath{\sim}4 K. The compounds ${\mathrm{PrFe}}_{4}$${\mathrm{P}}_{12}$ and ${\mathrm{NdFe}}_{4}$${\mathrm{P}}_{12}$ display features that suggest the occurrence of antiferromagnetic ordering below \ensuremath{\sim}6.2 K and ferromagnetic ordering below \ensuremath{\sim}2 K, respectively. Isothermal magnetization curves for ${\mathrm{PrFe}}_{4}$${\mathrm{P}}_{12}$ below 6 K reveal a spin-flop or metamagnetic transition.
TL;DR: The modified version of rapid imaging, where thephase rotation due to the phase encoding process is compensated for in each time interval, can have sensitivity superior to the original version where the phase rotation is not compensated for.
Abstract: The steady-state magnetizations in three versions of rapid NMR imaging using small flip angles and short repetition intervals are studied. It is shown that in the original version, the estimation using (1 - E1) sin ?/(1 - E1 cos ?) contains errors that depend on the increment of the phase rotation angle arising from the phase encoding process. The modified version of rapid imaging, where the phase rotation due to the phase encoding process is compensated for in each time interval, can have sensitivity superior to the original version where the phase rotation is not compensated for. Here, flip angles larger than the Ernst angle must be used. In the third version, the steady-state magnetization is obtained by a rapid imaging sequence in which the phase rotations arising not only from the application of the phase encoding gradient but also from the applications of other gradients are compensated for. Analysis of this version showed a remarkable increase in sensitivity although it required the use of an extremely uniform field. It is estimated that this increase reaches 80 percent with a repetition interval of 10 ms, although a field uniformity less than 1 ?T is necessary.
TL;DR: In this article, the magnetic properties of a series of ternary compounds of the composition RFe 10 V 2 (R ≡ Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu and Y) X-ray diffraction showed that these materials crystallize in the tetragonal ThMn 12 structure.
Abstract: We have studied the magnetic properties of a series of novel ternary compounds of the composition RFe 10 V 2 (R ≡ Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Lu and Y) X-ray diffraction showed that these materials crystallize in the tetragonal ThMn 12 structure The Curie temperature falls into the range 483 to 616 K From high-field magnetic measurements made at 42 K on aligned powders it was derived that the iron sublattice anisotropy is about 4 T, while the rare earth sublattice anisotropy is comparatively low in most of the compounds studied
TL;DR: In this paper, the spin precession of positive muons has been observed in the antiferromagnetic state of La2CuO(4y), and the long-lived precession signal indicates a microscopically homogeneous distribution of spin density at each Cu atom below the Neel temperature.
Abstract: Zero-field spin precession of positive muons has been observed in the antiferromagnetic state of La2CuO(4-y). Sharp onsets of the sublattice magnetization are found at temperatures close to those of the susceptibility maxima of different specimens. The long-lived precession signal indicates a microscopically homogeneous distribution of spin density at each Cu atom below the Neel temperature. A combination of the present results and neutron-scattering studies indicates the ordered moment per Cu atom to be significantly less than 1 mu(B).
TL;DR: In this article, the temperature dependence of the coercivity of Nd15(Fe1−xCox)77B8 and (Nd 1−xDyx)15Fe77B 8 sintered magnets and that of saturation magnetization (Ms) and the anisotropy field (HA) was investigated using the μ0HA vs μ0HcI+Ms plot.
Abstract: The temperature dependence of the coercivity (HcI)of Nd15(Fe1−xCox)77B8 and (Nd1−xDyx)15Fe77B8 sintered magnets and that of the saturation magnetization (Ms) and the anisotropy field (HA) of Nd2(Fe1−xCox)14B and (Nd1−xDyx)2Fe14B single crystals have been observed in the temperature range between 295 and 800 K. The dependence of the coercivity on the major magnetic properties of the matrix phase in the Nd‐Fe‐B based magnets are investigated using the μ0HA vs μ0HcI+Ms plot. It is demonstrated that this method of analysis is useful in studying the coercivity mechanism of the Nd‐Fe‐B based sintered magnets.
TL;DR: In this paper, specific heat, magnetization, and transport properties (resistivity, thermoelectric power, and thermal conductivity) of single-crystal CeCu6 are reported with special emphasis on the effect of magnetic field.
Abstract: Measurements of the specific heat, magnetization, and transport properties (resistivity, thermoelectric power, and thermal conductivity) of single-crystal CeCu6 are reported with special emphasis on the effect of magnetic field. The relative field variations of the differential susceptibility, the coefficients of the linear temperature term of the specific heat, and theT
2 resistivity term are presented. They are directly related to the field curvature of the magnetization, indicating the itinerant nature of thef electrons. The Wilson ratio reaches a maximum atH=H*, which may correspond to a crossover from a low-field phase in which antiferromagnetic correlations dominate, to a highly polarized phase. Intersite coupling seems to play an important role in heavy-fermion compounds. Another interesting result is the occurrence of residual positive magnetoresistivity, which also appears to be a general feature of heavy-fermion compounds. The properties of CeCu6 are compared to those of otherf instability compounds and to present theories.
TL;DR: In this article, a generalized Hubbard model is proposed to account for the unusual ferromagnetic exchange interactions in this system and the results are consistent with a crossover from a dominance of one-dimensional magnetization interaction to a 3D mean-field-like interaction at Tl4.8 K.
Abstract: The temperature and magnetic field dependence of the magnetization and susceptibility of single-crystal decamethylferrocenium tetracyanoethenide (DMeFc TCNE) demonstrate that this material is the first molecular compound with a ferromagnetic ground state. A spontaneous magnetization is observed for Tl4.8 K. The results are consistent with a crossover from a dominance of one-dimensional ferromagnetic exchange interaction to a 3D mean-field-like interaction at \ensuremath{\sim}16 K. The critical exponents are in accord with mean-field behavior. A generalized Hubbard model is proposed to account for the unusual ferromagnetic exchange interactions in this system.
TL;DR: In this article, a model for the stress-dependent effective field was presented, which when used in conjunction with the Jiles-Atherton theory, qualitatively accounts for the change in slope and shape of the hysteresis curves with uniaxial stress and convexity of the curves depicting remanent and peak magnetization as a function of stress.
Abstract: A model is presented for the stress‐dependent effective field, which when used in conjunction with the Jiles–Atherton theory, qualitatively accounts for (1) the change in slope and shape of the hysteresis curves with uniaxial stress and (2) the convexity of the curves depicting remanent and peak magnetization as a function of stress. Also, the model can produce the Villari reversal if parameters are selected appropriately.
TL;DR: Two samples of Dy-Y superlattices produced by molecular-beam-epitaxy techniques are shown by neutron diffraction to order magnetically in a helix which is incommensurate with the bilayer thickness, indicating a second order irreversible transition to a metastable ferromagnetic state.
Abstract: Two samples of Dy-Y superlattices produced by molecular-beam-epitaxy techniques are shown by neutron diffraction to order magnetically in a helix which is incommensurate with the bilayer thickness. One sample consists of 64 bilayers, each bilayer made up of about 15 growth planes (42 A) of Dy atoms followed by 14 planes (38 A) of Y atoms. The second sample has 90 layers, each layer consisting of 9 Dy atomic planes and 8 Dy/sub 0.5/Y/sub 0.5/ alloy planes. The phase coherence of this ordering extends over several bilayers, and is especially striking in the sample where the layers of localized Dy spins are separated by 14 atomic planes of nonmagnetic Y. The fact that the helix chirality propagates across several bilayers rules out a simple scalar Ruderman-Kittel-Kasuya-Yosida coupling between the Dy planes on either side of an Y layer, but suggests instead that a helical spin density wave is induced in the Y conduction electrons. A simple model for the superlattice structure factor demonstrates that observed asymmetries in the magnetic diffraction-peak intensities can be ascribed to the existence of different magnetic modulation wave vectors in each layer type (Dy and Y). In these superlattices the strain clamping by the intervening non-Dymore » layers and the substrate suppresses the first order ferromagnetic transition found in bulk Dy in both zero and finite fields. Although the planar magnetostriction is clamped, it is observed that the application of a magnetic field in the basal plane produces at low temperatures a second order irreversible transition to a metastable ferromagnetic state. At high temperature the magnetization process is initiated by a reduction of the helical coherence length due to a random-field coupling to the uncompensated Dy layer moment.« less
TL;DR: In this article, the intrinsic activation energy of Nd-Fe-B sintered magnets was derived at different fields between 4.2 and 300 K. At a given temperature, the viscosity S (H ) and the irreversible susceptibility χ irr were found to be proportional.
TL;DR: In this paper, the most recent results concerning magnetic susceptibility, Mn++−Mn++ nearest neighbor exchange, and magnetic short-range order in DMS are reviewed and a unified picture of magnetic properties of DMS is presented.
Abstract: Diluted magnetic semiconductors (DMS) are semiconducting alloys containing a random distribution of substitutional magnetic ions (e.g., Mn++ in Cd1−xMnxSe). Magnetic properties of DMS—such as spin glass behavior due to lattice frustration, magnon excitations in a random system of spins, superexchange, and short range antiferromagnetic order—are of considerable interest in their own right. In addition, understanding these properties is important because they strongly influence the electronic phenomena in DMS via the sp‐d exchange interaction between the band electrons and the localized magnetic moments. We review the most recent results concerning magnetic susceptibility, Mn++‐Mn++ nearest‐neighbor exchange, and magnetic short‐range order in these materials. On this basis, we can present a fairly complete and unified picture of magnetic properties of DMS. In addition, we point out some of the issues and challenges that lie ahead.
TL;DR: In this article, the authors measured the change of magnetization with time in the presence of a constant field or by measuring the dependence of the hysteresis loop on the field sweep rate.
Abstract: Time‐dependent magnetic phenomena in oxide particulate recording materials are observed by measuring the change of magnetization with time in the presence of a constant field or by measuring the dependence of the hysteresis loop on the field sweep rate. Either type of experiment yields a measured value of the coercivity as a function of the characteristic measurement time. For a constant‐field experiment, this time is simply the interval needed for the applied field to reduce the magnetization from saturation remanence to zero. A corresponding time, approximately inverse to the sweep rate, can be associated with the coercivity measured in a swept‐field experiment. A time‐dependence parameter that measures the strength of the dependence of magnetization on time at constant field and also that of coercivity on sweep rate in a swept‐field experiment can be determined. This parameter can be interpreted, using simple kinetic theory, to estimate the volume of the magnetic switching unit. Volumes estimated in th...
TL;DR: In this article, the authors measured the pressure effect on the magnetic transition temperatures of Mn 3 GaC, Mn 3 ZnC and Mn 3 SnC under pressures up to 13 kbar.
Abstract: The pressure effect on the magnetic transition temperatures of Mn 3 GaC, Mn 3 ZnC and Mn 3 SnC were measured under pressures up to 13 kbar. The pressure derivatives of the transition temperatures are obtained to be d T t /d P =-3.5 K/kbar and d T C /d P =0.4 K/kbar for Mn 3 GaC, d T t /d P =-0.9 K/kbar and T C /d P =0 for Mn 3 ZnC and d T C /d P =-1.9 K/kbar for Mn 3 SnC, where T t and T C are the magnetic order-order transition temperature and the Curie temperature, respectively. An intermediate magnetic phase (I) is induced in Mn 3 GaC under pressures above 3 kbar. The triple point (Antiferro./I/Ferro.) was determined to be T c =158 K and P c =3 kbar. The temperature variations of magnetization, magnetic susceptibility and latlice parameter were also measured.
IBM1
TL;DR: Mesure de l'aimantation induite optiquement dans un echantillon de Cd 0,8 Mn 0,2 Tc de 10 μm de diametre : elle depend de l-energie and de the polarisation du rayonnement d'excitation, et les spins perturbes retrouvent un equilibre par relaxation spin-reseau.
Abstract: A newly developed integrated SQUID magnetic spectrometer yields direct high-resolution measurements of the optically induced magnetization in a 10 \ensuremath{\mu}m-diam sample of ${\mathrm{Cd}}_{0.8}$${\mathrm{Mn}}_{0.2}$Te. Both the magnitude and the picosecond dynamics of the magnetic response have been studied and are seen to be dramatically dependent on the energy and polarization of the optical excitation. The data show that the overall sample magnetization changes upon illumination, and that the perturbed spins equilibrate through spin-lattice relaxation.
TL;DR: In this paper, the magnetic properties of several specimens of steel in which the carbon content has been deliberately reduced are investigated so that the more subtle effects on magnetic properties caused by these other factors can be determined.
Abstract: The effects of carbon on the magnetic properties of steel have been of great interest over the years both because of the great commercial importance of steel and because it is known that carbon is the most important single factor affecting the magnetic properties of steel. Slight changes in the amount and distribution of the carbon content can completely mask any changes due to grain size, stress, and the effects of other impurities. The magnetic properties of several specimens of steel in which the carbon content has been deliberately reduced are investigated so that the more subtle effects on magnetic properties caused by these other factors can be determined. The results presented include magnetic Barkhausen measurements, magnetoacoustic emission measurements, and magnetization data. The grain structure of each specimen was closely monitored and the resulting magnetization data correlated with the microstructure.
TL;DR: In this paper, magnetic moments of about 3μB/U at high temperature and U-U distances from 3.51 to 4.68 A were measured for several equiatomic ternary intermetallic compounds of formula RTX with R = U, Th, Hf and Ti, T a transition metal (Co, Ni, Ru, Rh, Pd, Ir, Pt and Au), and X = Al, Ga, Sn and Sb).
TL;DR: In this paper, the authors showed that saturation can be achieved at a field lower than the magnetization in a multilayer with alternating ferromagnetic and nonmagnetic layers assuming that the stripe domains are oriented only up or down along the anisotropy axis.
Abstract: In a ferromagnetic thin film with strong perpendicular anisotropy, saturation may be reached at fields lower than the magnetization. This field is calculated for a multilayer with alternating ferromagnetic and nonmagnetic layers assuming that the stripe domains are oriented only up or down along the anisotropy axis. The results are compared with experimental data on Pd/Co multilayers with ultrathin Co layers. The agreement is very good if we take σw=1×10−3 J/m2 as the energy of walls between the domains. It is argued also that with other materials, high perpendicular relative remanence may be achieved when multilayers with suitable parameters are used.