Rare Earth-transition Metal Alloys Research Articles

Permanent magnet films for applications in microelectromechanical systems

This paper reviews several promising permanent magnet (PM) films used for the applications in microelectromechanical system (MEMS). Selection rules for PM films are elucidated. Currently in use or developing PM films, including rare-earth magnet alloys, transition-metal alloys and hard ferrites, are critically assessed. To meet the MEMS requirements, a permanent magnet film must possess, in addition to high magnetic performance at the service temperature, the adaptability to IC processing as well as environmental stability. Rare-earth magnet films showing the best magnetic performance are not necessarily the best choice for MEMS applications, due to the high corrosion rate. The PtFe or PtCo films and the hybrid-magnet thick-films (composed of a photo-lithographable resin and a magnet powder) show greater potential in future MEMS applications.

The effect of boron on the uniaxial magnetic anisotropy energy and the polar Kerr rotation in amorphous NdFe films

Amorphous light rare earth–transition metal alloys are candidates for magneto-optical recording materials in the wavelength region of a blue laser beam (λ≈400 nm) due to the large Kerr rotation angle θK. However, the large demagnetizing energy (shape anisotropy) prevents the films from developing an effective perpendicular anisotropy. The addition of boron to the amorphous Nd Fe matrix reduces the magnetization, enhances the effective perpendicular anisotropy, and enhances the Kerr rotation angle θK.

Thermal effects on two-sublattice magnetic systems

We report on the thermal effects on a two-sublattice system in the mean field approximation using computer simulation. In particular we study the temperature dependence of magnetization, magnetic susceptibility, and magnetic heat capacity for a system in which the magnetic state is determined by the magnetic anisotropies of the two components of the compound and the exchange interaction energy between them. The partition function is first determined, subsequently the magnetic properties are derived from the partition function. In certain cases, the findings of the model are compared with experimental data on rare-earth transition metal alloy system.

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.

New Magnetic Recording Method Using Laser Assisted Read/Write Technologies

We have developed a new magnetic recording method which is kind of a fusion technology of optical recording and magnetic one. Ferrimagnetic rare-earth transition metal (RE-TM) alloys whose magnetic compensation temperatures are around room temperature are employed for magnetic recording materials. Their unique temperature dependence of the magnetic properties is essential to the new method. Laser assisted writing brings about a narrow track width, compared with a magnetic head width. Laser assisted reading is capable of detecting leakage flux from only the heated area with less crosstalk of neighboring tracks. We found that this new magnetic read/write method is functioning successfully.

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.

Magneto-optical properties and stability of GdTbFeCo thin films prepared by RF-magnetron sputtering

Amorphous GdTbFeCo alloy thin films have been deposited onto glass substrates by RF-magnetron sputtering from a mosaic target. The polar Kerr magneto-optical (MO) rotations for GdTbFeCo thin films were measured by using computer controlled rotating analyzer apparatus in applied magnetic fields of up to 6.5 kOe at room temperature and a HeNe laser wavelength of 633 nm. It was found that as the incident RF power is held constant, the pressure of sputtering gas argon strongly affects the MO properties and stability of GdTbFeCo thin films. The Kerr MO rotation angle is as high as 0.38° for as-deposited GdTbFeCo thin films without a protective layer at an argon pressure of 1 Pa. In this study the obtained correlations of deposition conditions, microstructure, MO property and stability make it possible to choose the optimal RF-magnetron sputtering parameters for fabricating the rare-earth—transition metal alloy thin films with high performances.

An alternative approach to the finely crystalline powder of rare earth-transition metal alloys

Small particulate alloys, Sm2Fe7, Nd2Fe7, NdFe10Mo2 and NbFe11 Ti, have been obtained by reduction-diffusion reactions from nanoscale precursors. The nanoscale oxide precursors, such as rare earth and transition metal oxides, were produced by sol-gel methods. After a preliminary H2 reduction treatment, the precursors were reduced by CaH2 under mild conditions. The obtained alloys are crystalline powders with small particle sizes and uniform size distributions.

Pulsed microwave plasma assisted chemical vapour deposition of diamond: J. Laimer, S. Matsumoto (Technical University, Vienna, Austria). Int. J. Refractory Metals Hard Mater., vol 14, no 1/3, 1996, 179–184

Under certain conditions, hydrogen can degrade the mechanical properties and fracture behavior of most structural alloys; however, it also has some positive effects in metals. Several current and potential applications of hydrogen for enhancing the production and processing of materials are reviewed. These include thermohydrogen processing (THP) and forming of refractory alloys, processing of rare earth-transition metal magnets by hydrogen decrepitation (HD) and hydrogenation–decomposition–desorption–recombination (HDDR), hydrogen-induced amorphization (HIA) and microstructural refinement, extraction of elements from ores and alloys, and the use of hydrogen as a reducing gas for welding and brazing. Hydrogen is found to enhance the formability, microstructure and properties of a large variety of materials, including steels, Ti-based alloys and metal matrix composites (MMCs), refractory metals and alloys, rare earth-transition metal alloys, metalloid-containing metallic glasses, etc.

Synthesis of silicides by mechanical alloying: K. Kobayashi, K. Miwa (National Industrial Research Institute, Nagoya, Japoan). J. Japan Soc. Powder Powder Metall., vol 42, no 1, 1995, 103–107. (In Japanese.)

Under certain conditions, hydrogen can degrade the mechanical properties and fracture behavior of most structural alloys; however, it also has some positive effects in metals. Several current and potential applications of hydrogen for enhancing the production and processing of materials are reviewed. These include thermohydrogen processing (THP) and forming of refractory alloys, processing of rare earth-transition metal magnets by hydrogen decrepitation (HD) and hydrogenation–decomposition–desorption–recombination (HDDR), hydrogen-induced amorphization (HIA) and microstructural refinement, extraction of elements from ores and alloys, and the use of hydrogen as a reducing gas for welding and brazing. Hydrogen is found to enhance the formability, microstructure and properties of a large variety of materials, including steels, Ti-based alloys and metal matrix composites (MMCs), refractory metals and alloys, rare earth-transition metal alloys, metalloid-containing metallic glasses, etc.

Synthesis of magnetic intermetallics and their interstitial hydrides

Many binary and ternary magnetic rare earth transition metal alloy powders have been synthesized by the oxygen-reduction-diffusion technique (ORD). Several levels of hydrogen concentration have been achieved by using chemical reactions where nascent hydrogen produced next to the surface of the alloy grains was observed to diffuse into the core of the particles at a temperature close to the ambient.

Mechanically alloyed Sm(CoFe) permanent magnets

The use of mechanical alloying as a processing method for the solid-state synthesis of new materials has received considerable attention in recent years. Of particular interest has been the synthesis of rare earth permanent magnet materials. Many of the rare-earth transition metal alloys studied to date exhibit similar structures and properties in the as-milled condition. In particular, the hard magnetic phase does not form during mechanical alloying. Instead, either a single amorphous phase is formed or a two-phase mixture is developed during milling which consists of crystallites of the transition metal, (i.e. Fe, Co), and an amorphous phase containing the rare earth element. Crystallization of the as-milled structure into a nanocrystalline hard magnetic phase (i.e. Nd{sub 2}Fe{sub 14}B or SmCo{sub 5}) normally requires a heat treatment at temperatures in the range of 600--700 C. With Sm{sub 2}Fe{sub 17}N{sub 2.7}, nitriding must be carried out after crystallization since Sm{sub 2}Fe{sub 17}N{sub 2.7} decomposes to samarium nitride and {alpha}-Fe at temperatures above 500 C. Mechanically alloyed and heat treated structures have been found to exhibit remarkably high values of coercivity, H{sub c}. For example, values of H{sub c} exceeding 75 kOe have been obtained in SmCo{sub 5}.

Thickness variation of the magneto-optical properties of Tb,Dy-FeCo,Pr thin films

The optimisation of magneto-optical data storage disk structures requires a knowledge of the optical and magneto-optical constants of the storage material. In this paper we present the optical (n + ik) and first order magneto-optical (Q1 + iQ2) constants for the rare earth-transition metal alloys: Tb23.5Fe72.5Co4.5, (Tb23.5Fe72.5Co4.5)89Pr11, Dy22Fe68.5Co9.5 and Dy28Fe52Co20. A combination of Kerr polarimetry and ellipsometry is used to evaluate these constants, which are then used to calculate the magneto-optic response as a function of magnetic layer thickness. A comparison between calculated and measured Kerr responses from both the air and substrate side of these structures reveals the self consistency of the modelling process and the validity of the determined constants.

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. >

Microstructural and magneto-optical characterization of ferrimagnetic multilayered thin-film rare-earth iron garnet heterostructures

The continuous demands of the computer industry for increased reliability, portability, and density of storage media, has opened a new chapter in the magnetic recording research, by focusing on the viability of magneto-optical materials for storage. Several materials are considered presently to be at the forefront of this new quest: ternary rare-earth transition-metal alloys (such as GdTbFe or TbFeCo), garnets, and Co/Pt or Co/Pd mutilayers. Of these, the ferrimagnetic garnets, due to their relatively flexible structure, may accommodate a large number of substituting ions, allowing thus for a very good control of their magnetic and magneto-optical properties. The good results obtained during thegrowth of epitaxial superconducting oxide thin films by pulsed laser deposition (PLD), has encouragedus to try this novel deposition technique in the growth of multilayered heteroepitaxial ferrimagneticiron garnet thin films.Superlattice heterostructures consisting of alternating single crystalline ferrimagnetic yttrium-iron-garnet (YIG) and bismuth-iron-garnet (BIG) thin film layers, as well as alternating YIG and europiumsubstituted BIG (EBIG), were deposited on single crystalline (111) paramagnetic gadolinium-galliumgarnet (GGG) substrates.

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.