Istraživanje procesa relaksacije ranih metastabilnih stanja sistema Fe40Ni40Si14B6

An investigation of the low-temperature relaxation process has been performed in which the structure of the frozen liquid metal is transformed into the structure which the sample acquires at the room temperature. The samples were obtained by quenching on a Cu single roll and then conserved at low temperature as soon as formed. It was noted that the activation of the relaxation process occurs in a temperature interval of 10-125 K. That is somewhat unexpected, because of the nature of the usual relaxation process in amorphous systems. The activation energy of the so-called early metastable states in Fe40Ni40Si14B6 amorphous system was found to be 1.5 kJ/moleU radu je opisano istraživanje niskotemperaturnog relaksacijskog procesa kojim se struktura zamrznutog tekućeg metala, dobijenog kaljenjem na jednom valjku, transformira u strukturu koju traka ima kada dostigne sobnu temperaturu. Uočeno je da se proces relaksacije počinje aktivirati pri određenoj energiji, što nije bilo za očekivati s obzirom da se radi o relaksacijskom procesu u amorfnom sistemu. Za aktivacijsku energiju kojom se relaksiraju rana metastabilna stanja u sistemu Fe40Ni40Si14B6 dobivena je vrijednost 1.5 kJ/mol

Tunable Magnetization and Damping of Sputter-Deposited, Exchange Coupled Py|Fe Bilayers

We report on magnetic damping of exchange coupled, polycrystalline Py(Ni80Fe20)|Fe and Fe|Py bilayers, prepared by sputter-deposition on an amorphous 3nm Ta seed layer. FMR measurements are performed on varying thicknesses of the individual Py and Fe layers while keeping the total bilayer structure thickness fixed. When Fe is grown directly on Ta, there is large magnetic inhomogeneity and damping. However, when a Py layer is deposited between Fe and Ta, both the magnetic inhomogeneity and damping significantly decrease even if Fe is covered by Ta. The intrinsic damping of the Ta|Py|Fe film can be further lowered by increasing the Fe to Py ratio. SQUID measurements show a linear increase in saturation magnetization with increasing ratio of Fe to Py. A combination of in-plane and out-of-plane X-ray diffraction measurements show that Py is textured along the ⟨111⟩ directions and Fe is textured along the ⟨110⟩, with Fe texture significantly improving if it is deposited on Ta|Py instead of Ta. By improving the texture of Fe by introducing a thin Py layer between Fe and Ta, one can grow Fe thin films with zero in-plane anisotropy, tunable magnetic moment, and low magnetic damping, approaching that of the best single crystal Fe

On the origin of noncollinear magnetization coupling across RuX layers

We present a simple atomistic model for the description of noncollinear coupling in magnetic multilayers with hybrid spacer layers made of Ru alloyed to ferromagnetic atoms such as Fe. In contrast to previous analytical and micromagnetic models that explain the noncollinear coupling by means of lateral fluctuations in the coupling constant, the presented model accounts for atom-atom coupling in all three spatial dimensions within the spacer layer. The new model is able to accurately predict the dependence of the macroscopic bilinear and biquadratic coupling constants on the spacer-layer composition and thickness, showing much better quantitative agreement than lateral-fluctuation models. Moreover, it predicts noncollinear coupling even for infinitely stiff ferromagnetic layers which goes beyond the predictions of previous models

Anti-ferromagnetically coupled perpendicular magnetic recording media with oxide. US Patent #7,842,409

The present invention relates to perpendicular magnetic recording media with improved signal-to-medium noise ratio (“SMNR”) and thermal stability, which media include a pair of vertically spaced-apart perpendicular ferromagnetic layers which are anti-ferromagnetically coupled (“AFC”) across a non-magnetic spacer layer. The invention is of particular utility in the fabrication of data/information storage and retrieval media, e.g., hard disks, having ultra-high areal recording/storage densities

Elemental site substitutions in R-Fe compounds

A model is proposed for calculating the probabilities of atomic substitutions (atom X for atom A) in different A-sites in an A-containing compound. The model consists of three terms. The first term describes the chemical affinity between the X or A atom and its nearest neighbours. The second term accounts for the elastic energy due to the volume mismatch between the X atom and the x A-site. The third term is a structural energy term and is present only for d-electron atoms and accounts for the preference of these metals to crystallize in the bcc, fcc or hcp structures depending on the number of valence electrons per atom. The probability of the substitution is calculated using the Boltzmann distribution assuming that each formula unit of the compound has a maximum of one X atom, and that the X atoms are uniformly distributed throughout the compound.The model was tested successfully for Fe-substitutions in various compounds. The experimental fractional site occupations of the X atoms in the Fe-sites were determined from neutron diffraction measurements. The results show that the model precisely determines the sites preferentially occupied by the X atoms; calculated values are within 40% of the experimental values for all X elements. Moreover, the model correctly predicts sites that are avoided by the X elements.The model calculations for site occupations show that all three terms have to be taken into account to give a quantitative explanation to the experimentally observed substitutions. The agreement between the experimental and calculated values obtained for Fe-substitutions in the 2-17, 3-29, 1-12 and 2-14-1 structures can be improved if the structural term for Fe is assumed to be zero as the Fe structural transition (from bcc to fcc) occurs near the annealing temperatures of the compounds and thus the difference in the structural energy between bcc-Fe and fcc-Fe could be neglected at that temperature. A further improvement can be made if one assumes that the sites which have an irregular shape, such as 9d (2-17), 8j1 (2-14-1), 2c, 4e, 8j4 (3-29) and 8f (1-12) have smaller "effective" volumes, i.e. the "effective" radii of the spherical holes are estimated from the average distances of the closest nearest neighbours. An understanding of the site substitution mechanisms in intermetallic compounds allows us to explain structure-sensitive physical phenomena even in cases where experimental structural data are unavailable. We have studied the anomalous thermal expansion along the c-axis in 2-17 compounds and the reduced rate of the nitrogen bulk diffusion in Nd2Fe 17-deltaXdelta for some X elements.The proposed model for calculating site occupancies is general in scope and can be applied to any intermetallic compound where the site occupations of elemental substitutions need to be determined. The model can be improved if one can determine the contribution of the structural term in the formation of compounds containing two or more transition metals. In order to improve the precision of the elastic term experimental data on the temperature dependence of the bulk and shear moduli of the elements and the compounds will be needed

Single-pass recording of multilevel patterned media. US Patent #7,974,031

A method of performing data/information recording and retrieval utilizing a multilevel patterned magnetic medium, comprises providing a magnetic recording system including a read/write head and a multilevel patterned magnetic recording medium including a plurality of spaced apart data/information storage elements each comprising a stacked plurality n of magnetic recording cells with different magnetic properties and magnetically decoupled from overlying and/or underlying cells; providing relative movement between the write head and magnetic recording medium; and writing to the medium by supplying the write head with a modulated write current comprising a plurality n of pulses of different magnitudes while the head passes over each element, thereby applying n different magnetic field strengths to each element, such that the writing occurs in a single pass of the write head over each element

Anti-ferromagnetically coupled soft underlayer. US Patent #7,666,529

A magnetic recording medium having a first magnetic layer, a spacer layer, and a second magnetic layer, in this order, wherein the spacer layer includes a non-magnetic layer and a thickness of the spacer layer is selected to establish anti-ferromagnetic coupling between the first magnetic layer and the second magnetic layer, and a thickness of both the first and second magnetic layers are less than a critical thickness for formation of stripe domains in the magnetic layers is disclosed

Low coupling oxide media (LCOM). US Patent #7,867,637

A low-coupling perpendicular magnetic recording media comprising a magnetic storage layer and at least one low saturation magnetization layer. The magnetic storage layer has a saturation magnetization between about 400-900 emu/cm3 and the at least one low saturation magnetization layer has a saturation magnetization below that of the magnetic storage layer