Amorphous Rare Earth-transition Metal Alloys Research Articles

Impact of interfaces on magnetic properties of Gdx(Fe90Co10)1−x alloys

A 5 nm thick ferrimagnetic film made of amorphous rare-earth transition-metal alloys Gdx(Fe90Co10)1-x was grown by physical vapor deposition. Its magnetic properties (coercivity, perpendicular magnetic anisotropy, and compensation composition at room temperature) were investigated for various buffer and capping layers in contact with a ferrimagnetic thin film. While Gdx(Fe90Co10)1-x appears to be amorphous for all the samples, it appears that (111) textured Cu is the best material to promote perpendicular magnetization. The large compensation composition change as a function of the magnetic film interface at room temperature is analyzed in terms of polarizability of the surrounding buffer and capping materials.

Anomalous magnetoresistance and Hall effect in amorphous Pt/TbFeCo thin films

Among the magnetic materials in technological usage, amorphous rare-earth transition metal (RE–TM) alloys are of great interest due to their adjustable magnetic properties and favorable perpendicular magnetic anisotropic (PMA) advantages. In this study, the properties of Tb25Fe61Co14 system with 2, 5, and 10 nm Pt underlayers have been systematically explored by X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature and magnetic field dependence of Hall resistivity, magnetoresistivity, and magneto-optic Kerr Effect (MOKE) measurements. According to the results, whole thin films are amorphous in nature and display an out-of-plane magnetic anisotropy without annealing. Increasing the Pt underlayer thickness helps the TbFeCo layer to reach significantly enhanced perpendicular magnetic anisotropic values and visualize the appearance of anomalous magnetoresistance in the Hall effect measurements. The thin films with 5 and 10 nm Pt underlayer has a ratio of remanence magnetization/saturation magnetization (MR/MS) of around 1, which is the out of plane direction of MOKE signal. Besides, the present study also includes some pieces of evidence that might be related to the Berry phase trend.

Local structure in amorphous Sm_xCo_{1-x}: a combined experimental and theoretical study

Using a combination of extended X-ray absorption fine structure measurements, stochastic quenching (SQ) calculations and Voronoi tessellation analysis, the local atomic environments in thin films of amorphous Sm_{x}Co_{1-x} (x = 0.10, 0.22 and 0.35) are investigated and also compared with crystalline stoichiometric Sm–Co alloys of similar compositions. It is found that the variations in local environment around Co atoms in the amorphous films increase with increasing x and that none of the films exhibit any pronounced short-range order around the Sm atoms. There are, however, signs of clustering of Sm atoms in the SQ-generated simulated amorphous materials.Furthermore, good agreement is observed between experimentally obtained parameters, e.g., interatomic distances and coordination numbers, and those extracted from the simulated alloys. This is a strong indication that SQ provides a powerful route to reliable local structure information for amorphous rare earth–transition metal alloys and that it could be used for designing materials with properties that meet the demands of specific applications.

Contributions of electron and phonon transport to the thermal conductivity of GdFeCo and TbFeCo amorphous rare-earth transition-metal alloys

We experimentally investigate the electron and phonon contributions to the thermal conductivity of amorphous GdFeCo and TbFeCo thin films. These amorphous rare-earth transition-metal (RE-TM) alloys exhibit thermal conductivities that increase nearly linearly with temperature from 90 to 375 K. Electrical resistivity measurements show that this trend is due to an increase in the electron thermal conductivity over this temperature range and a relatively constant phonon contribution to thermal conductivity. We find that at low temperatures (∼90 K), the phonon systems in these amorphous RE-TM alloys contribute ∼70% to thermal conduction with a decreasing contribution as temperature is increased.

Large spontaneous Hall angle in [Co, CoFe/Pt] multilayer

We have quantitatively investigated the Hall effect in [Co, CoFe/Pt] multilayer films. The [Co, CoFe/Pt] multilayers exhibit large spontaneous Hall resistivity ( ρ H) and Hall angle ( ρ H/ ρ). Even though the Hall resistivity in [Co, CoFe/Pt] multilayer films (2.7–4 × 10 −7 Ω cm) is smaller than that of amorphous RE–TM alloy films which show large spontaneous Hall resistivity (<2 × 10 −6 Ω cm), the Hall angle of multilayer (6–8%) is almost twice than that in amorphous rare earth–transition metal alloy films (∼3%). The Hall angle provides evidence of the effects of the exchange interaction of the Hall scattering. The exchange is between conduction electron spins and the localized spins of the transition metal. The large Hall angle of [Co, CoFe/Pt] multilayer can be considered due to the high spin polarization and high Curie temperature of Co and CoFe transition metal layers. Even though the role of interfaces and surfaces in the magnetic properties of multilayer films may dominate that of the bulk, the Hall effects in [Co, CoFe/Pt] multilayer may be mainly dominated by the bulk effect.

A simple method for forming amorphous rare earth-transition metal alloy nanotube arrays

Arrays of rare earth-transition metal alloy Co 68Nd 32 and Co 96Sm 4 nanotubes, with amorphous structures and outer diameters of ca. 270–330 nm and with lengths of over 30 μm, have been fabricated for the first time by direct current electrodeposition with a mercury cathode via anodic aluminum oxide (AAO) template. The using of mercury cathode is a crucial condition for the growth of nanotubes and the co-reduction of Co 2+, Nd 3+ and Sm 3+ in aqueous solution without any chemical modification of the pores of AAO, since the liquid mercury has characters of excellent conductivity and fluidity, high surface tension, high photoelectric work function, and high over-potential. A possible growth mechanism for the nanotubes is proposed. The as-prepared nanotube arrays display low coercivity and uniaxial magnetic anisotropy, and the easy magnetization direction is perpendicular to the nanotubes axes.

CLUSTER-VARIATIONAL TREATMENT OF DISORDERED MIXED SPIN ISING MODEL

A disordered alloy ApB1-pwhere both A and B represent magnetic atoms with respective spins SA= 1/2 and SB= 1 and whose magnetic interaction can be described by the Ising Hamiltonian is treated using the cluster-variational method. In this method, it is assumed that the system is built out of a "building block" which is embedded in an effective field. Taking the "building block" as a 4-atom cluster, the approximate free energy of the alloy is then obtained by treating the interactions between spins within the cluster of all possible configurations in an exact manner and the rest of the interaction by an effective variational field. The magnetization M and the transition temperature Tcare then calculated for different concentration and exchange parameters (JAA, JBBand JAB). The magnetization M exhibits different kinds of ferrimagnetic behavior depending on the concentration and the relative strengths of the intra- and inter-sub-network exchange interactions. For antiferromagnetic JAB, the sub-network magnetization saturates and is aligned antiferromagnetically at low temperature. The existence of the compensation temperature, Tcm, where the total magnetization reverses its direction, and depends sensitively on the relative values of JAA/JABand JBB/JABand p. For B (A)-rich alloy with small JAB, the direction of the net magnetization remains unchanged up to Tc, and a maximum in M appears at intermediate T &lt; Tcwhen JBB≫ JAA(JBB≪ JAA). When |JAB| &gt; JAA, JBB, Tcexhibits a maximum with p. The transition temperature is much less than the mean-field value in all cases. The magnetic susceptibility diverges as T tends to Tcand is Curie-Wiess like at T ≫ Tc. The meta-magnetic behavior has been found at high magnetic fields. Some of these results are in tune with the experimental observations in the amorphous rare-earth transition metal alloys.

Structure and properties of amorphous thin film for optical data storage

In this paper the magnetic and magneto-optical properties of amorphous rare earth-transition metal (RE-TM) alloys as well as the magnetic coupling in the multi-layer thin films for high density optical data storage are presented. Using magnetic effect in scanning tunneling microscopy the clusters structure of amorphous RE-TM thin films has been observed and the perpendicular magnetic anisotropy in amorphous RE-TM thin films has been interpreted. Experimental results of quick phase transformation under short pulse laser irradiation of amorphous semiconductor and metallic alloy thin films for phase change optical recording are reported. A step-by-step phase transformation process through metastable states has been observed. The waveform of crystallization propagation in micro-size spot during laser recording in amorphous semiconductor thin films is characterized and quick recording and erasing mechanism for optical data storage with high performance are discussed. The nonlinear optical effects in amorphous alloy thin films have been studied. By photo-thermal effect or third order optical nonlinearity, the optical self-focusing is observed in amorphous mask thin films. The application of amorphous thin films with super-resolution near field structure for high-density optical data storage is performed.

Soft X-ray resonant magnetic scattering study of magnetization reversal in low dimensional magnetic heterostructures

Soft X-ray resonant magnetic scattering (SXRMS) has been used to investigate the microscopic magnetization reversal behavior of complex magnetic systems. SXRMS is a unique technique, providing chemical, spatial and magnetic sensitivity, which is not affected by external magnetic fields. The study of two selected thin magnetic heterostructures is presented, amorphous rare-earth transition metal alloys and perpendicular exchange coupled antiferromagnetic/ferromagnetic films. In the first system, the internal structure of magnetic stripe domains on nanometer length scales is obtained by measuring bi-dimensional (2D) scattering images. In the second system, the element specificity is exploited to identify the role of the uncompensated spins in the antiferromagnetic layer on the exchange coupling phenomena. Future trends are also discussed.

L'automatisation vers une offre standardisée

Among the magnetic materials in technological usage, amorphous rare-earth transition metal (RE–TM) alloys are of great interest due to their adjustable magnetic properties and favorable perpendicular magnetic anisotropic (PMA) advantages. In this study, the properties of Tb25Fe61Co14 system with 2, 5, and 10 nm Pt underlayers have been systematically explored by X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature and magnetic field dependence of Hall resistivity, magnetoresistivity, and magneto-optic Kerr Effect (MOKE) measurements. According to the results, whole thin films are amorphous in nature and display an out-of-plane magnetic anisotropy without annealing. Increasing the Pt underlayer thickness helps the TbFeCo layer to reach significantly enhanced perpendicular magnetic anisotropic values and visualize the appearance of anomalous magnetoresistance in the Hall effect measurements. The thin films with 5 and 10 nm Pt underlayer has a ratio of remanence magnetization/saturation magnetization (MR/MS) of around 1, which is the out of plane direction of MOKE signal. Besides, the present study also includes some pieces of evidence that might be related to the Berry phase trend.

Les échos

Among the magnetic materials in technological usage, amorphous rare-earth transition metal (RE–TM) alloys are of great interest due to their adjustable magnetic properties and favorable perpendicular magnetic anisotropic (PMA) advantages. In this study, the properties of Tb25Fe61Co14 system with 2, 5, and 10 nm Pt underlayers have been systematically explored by X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature and magnetic field dependence of Hall resistivity, magnetoresistivity, and magneto-optic Kerr Effect (MOKE) measurements. According to the results, whole thin films are amorphous in nature and display an out-of-plane magnetic anisotropy without annealing. Increasing the Pt underlayer thickness helps the TbFeCo layer to reach significantly enhanced perpendicular magnetic anisotropic values and visualize the appearance of anomalous magnetoresistance in the Hall effect measurements. The thin films with 5 and 10 nm Pt underlayer has a ratio of remanence magnetization/saturation magnetization (MR/MS) of around 1, which is the out of plane direction of MOKE signal. Besides, the present study also includes some pieces of evidence that might be related to the Berry phase trend.

Characterization of Perpendicular Recording Media of CoPtCrO Granular Thin Films.

Thermal stability of CoPtCrO granular thin films with perpendicular magnetic anisotropy is investigated. Magnetization decay with time M(t) exhibits almost a linear dependence with ln(t), similar to that for longitudinal recording media. In comparison with amorphous rare earth-transition metal alloys media which shows a non-linear decay with ln(t), the differences in magnetization reversal process and energy barrier distribution are discussed. From magnetic viscosity measurements, activation volume is determined and shows a minimum of about 2x10-18 cm3 for CoPtCrO at fields near its coercivity, leading to a coupled region of 10 nm average diameter. Also recording performance is investigated using a conventional merged GMR head and magnetic force microscope. The linear recording density dependence of signal amplitude reveals that the 50% rolloff density D50 is about 300 kfci.

High exchange bias field induced in ferrimagnetic bilayers of amorphous rare earth–transition-metal alloys

The magnetic reversal processes of exchange-coupled double layers (ECDL) and corresponding single layers of rare-earth–transition metal were studied by magneto-optical Faraday rotation (FR). The dependence of FR on the temperature shows a transition of DyFeCo/TbFeCo ECDL from one type to another near the compensation temperature of single layers. Minor and major hysteresis loops allowed us to measure the exchange bias field induced by DyFeCo, which has also been calculated with an analytical model. We have also observed that an unusual hystersis loop appears few celsius degrees before this transition occurs. In this letter, we analyze and describe different magnetization states, and various kinds of magnetization processes, including the usual and unusual FR loops, are explained in detail.

Selective 2p-3d electron orbits exchange coupling in amorphous rare earth-transition metal-boron alloys

One of the major bottlenecks in amorphous light rare earth-transition metal (LRE-TM) alloy films for magneto-optic (MO) recording media in blue wavelengths (/spl sim/400 nm) is the large demagnetization energy (E/sub D/), which originates from shape anisotropy of the samples and decreases the effective magnetic anisotropy energy K/sub Ueff/ perpendicular to the film planes. The reduction of this demagnetization energy and enhancement of polar Kerr rotation angles (/spl theta//sub K/) are attempted by the addition of boron (B) into the amorphous LRE-TM films, such as amorphous (NdFe)/sub 100-X/B/sub X/ films. The additive B plays the role of reducing an Fe sub-magnetic moment by selective 2p-3d electron orbits exchange coupling (SEC) between B and Fe. The SEC results in the reduction of E/sub D/, enhancement of K/sub Ueff/ and increase of /spl theta//sub K/ in the amorphous (NdFe)/sub 100-X/B/sub X/ alloy films.

Present and future of magnetooptical recording materials and technology

Erasable optical information storage from amorphous rare earth-transition metal (RE-TM) alloys media has led to impressive improvements towards hyper high density recording in the past five years. Write/erase and readout processes are based on light-induced thermomagnetic switching of magnetic domains and magnetooptical (MO) Kerr effect, respectively, in ferrimagnetic films exhibiting a uniaxial magnetic anisotropy. The route towards ultrahigh optical areal densities was open from the beginning of the nineties from two key technologies related to near field optical techniques and RE-TM exchange-coupled bi, tri- and multilayers. The performances of the MO media depend on the types and states of these multilayers with perpendicular or mixed (perpendicular and planar) anisotropies which change with the temperature and the applied field. The development of the thermomagnetooptical materials is discussed with reference to their magnetic and MO properties to increase the density storage.

Kerr effect enhancement by photon tunneling and possible application to a new scanning probe magnetic microscope

Magneto-optical effects are calculated for the film stack consisting of hemisphere glass/magnetic film (10 nm)/air gap (d nm)/glass plate. Polarized light (wave length=800 nm) is irradiated through the hemisphere glass in the total internal reflection configuration. A typical amorphous rare earth-transition metal alloy is used for the magnetic layer. We find a large monotonic change in the figure of merit (product of the reflected amplitude of light and the Kerr rotation angle) as a function of the air gap, ranging from 1 to 800 nm. Similar results are obtained for a magnetic film with a 10 nm SiO2 protective layer and for a 1-nm-thin magnetic film. This phenomenon is mostly caused by a change in the reflectivity at magnetic film/air interface due to photon tunneling. The difference in the figure of merit between perpendicular and longitudinal magnetization is about 0.6°. These results imply that it might be possible to obtain an image of perpendicular magnetic moment with photon scanning tunnel microscopy (STM). This method can be combined simultaneously with a conventional atomic force microscope or STM.

Evaluation of Anisotropic Film Structure of Amorphous Alloy by Computer Simulation

ABSTRACTA film growth of a virtual GdCo amorphous binary alloy was studied with a molecular dynamics simulation. A deviation of the atomic environment δ and an atomic pair distribution index η were calculated to evaluate the atomic structure of the prepared film. It was found that an anisotropic atomic distribution is induced in the film. The value of δ for a Gd atom environment is of the order of 10−4 and is almost in quantitatively agreement with the experimental value. The anelastic deformation is affected by the roughness of the substrate and becomes large in the film deposited on a smooth substrate. The value of η shows that the atomic pairs preferentially orient toward a horizontal film plane. The obtained results strongly support a single ion model as a main origin of a perpendicular magnetic anisotropy experimentally observed in amorphous rare earth-transition metal alloy films.

Magnetic and magnetostrictive properties of amorphous rare earth-transition metal alloy films

The magnetic and magnetostrictive properties of amorphous binary TbxFe100-x and DyxFe100-x and amorphous ternary (TbxDy1-x)20Fe80, (TbxDy1-x)33Fe67 and (TbxDy1-x)43Fe57 thin films are presented. The films were prepared by sputter deposition from composite targets onto nominally room temperature substrates. Magnetization, coercivity and magnetostriction measurements reflect the compositional dependence of the easy direction of magnetization in the films. In-plane magnetostrictions of over 300*10-6 were measured for some of the TbxFe100-x and (TbxDy1-x)43Fe57 films.

Microstructure of Re-Tm films and anisotropy of domain wall motion

The structure of thin amorphous rare earth-transition metal (Re-Tm) alloy films and domain wall propagation in these films were studied with the help of scanning tunneling microscopy and magnetooptical techniques. The anisotropic displacement of the domain walls arising from the anisotropic film structure was found in the films investigated. >

The magnetic phase transition in amorphous rare earth-transition metal alloys

The magnetic phase transition of amorphous RE-TM alloys is investigated by measuring the magnetic moment as function of the temperature and the applied field. The samples are producedby both the melt-spinning technique (Fe30Tb70, Fe33Gd67) and the rf-sputtering technique (Fe67Tb33, Fe51.6Al15.4Tb33). The critical exponents β, γ ', γ and δ, as well as the reduced critical amplitudes J0/JS(0), μh0/(kBTc) and DJ0μh0 are determine d to obtain a complete overview on the behavior of the magnetic phase transition. The critical exponents β, γ' and γ are determined by two independent methods: Modified Arrot plots and the method of scaling plots. As a further method for the determination of the critical exponents β and γ, we have used the method of Kouvel and Fisher. The critical exponent δ is determined from In J versus In(μ0H) plots. The critical exponent values found in general cannot be related definitely to any theoretical prediction, except for Fe30Tb70, for which the critical exponents agree rather well with the values derived for the three dimensional Heisenberg model. Furthermore, the critical amplitude values show significant deviations from the theoretical values as derived for different models.