Z.S. Shan

Magnetic hardening in FePt nanostructured films

FePt films have been prepared by sputtering Fe/Pt multilayers onto glass or silicon substrates. The thickness of the Fe and Pt layers was adjusted with the Fe:Pt atomic ratio from about 1:1 to 2:1. Magnetic hardening is observed after heat treatment at elevated temperatures, which led to coercivity values exceeding 20 kOe in samples with an Fe:Pt ratio around 1.2:1. The hardening originates from the formation of the tetragonal FePt phase with high magnetocrystalline anisotropy and a favorable microstructure. Two-phase composite films containing hard and soft phases were obtained when the Fe:Pt ratio increased. Under optimized processing conditions, composite films with energy products larger than 30 MG Oe at room temperature have been successfully produced.

The process‐controlled magnetic properties of nanostructured Co/Ag composite films

Nanostructured Co/Ag composite films were prepared by magnetron sputtering using a single target. The average crystallite sizes of Co and Ag in the films depend on the deposition conditions. As the substrate temperature increases from 100 °C to 600 °C, the average Ag crystallite size increases from 39 to 452 A, and the average Co crystallite size increases from <30 to 297 A in the film with 39 vol. % of Co. The films with 39 vol. % of Co and prepared at 400 °C substrate temperature showed a maximum magnetic coercivity of 565 Oe at 6 K. We have studied the correlation between the structure and magnetic properties of these films.

Magnetization reversal and defects in Co/Pt multilayers

(Co 3 A/Pt 10 A)×N (N=8, 16, and 30 bilayers) multilayer thin films were prepared by sputtering onto an 850‐A‐thick SiN layer that had been deposited on a silicon (111) substrate. We used the polar Kerr effect to measure the time dependence of magnetization reversal over the temperature range 90–300 K. Direct domain observations were also carried out. The results show that the domain expansion process depends strongly on the number of bilayers. Uniform domain expansion was found only in the thinner samples. From the time dependence of the magnetization reversal measurements over the temperature range 90–300 K, the activation energy and volume associated with domain wall motion were found to be 1.2 eV and 2.3×10−18 cm3 for N=8 sample. The N=16 and N=30 samples seem to have a broad distribution of activation energies. Our observations suggest that both the coercivity and magnetization reversal are controlled by the defects that come from the interface between the Co and Pt.

Temperature and thickness dependence of coercivity and magnetization of Co/Cu and Co/Si multilayers

Co/Cu and Co/Si multilayers of total thickness ∼3000 A were prepared by rf and dc magnetron sputtering. The nominal thicknesses of the individual layers were in the range of 4 to 100 A. A large coercivity (Hc) at 10 K was observed for very thin layers of Co in Co/Cu samples, and it decreased with increase of the Co layer thickness. For very thin layers of Co in Co/Cu samples, the layer behaved superparamagnetically. Similar behavior was not to be observed in Co/Si samples. With increased substrate temperature (Ts) during deposition, Hc was also observed to increase (decrease) for Co/Cu (Co/Si) samples. Magnetization data were modeled to determine the diffusion layer thicknesses.

Magnetic properties, anisotropy, and microstructure of sputtered rare‐earth iron multilayers

A study of compositionally modulated magnetic films of the form Fe/RE, particularly for RE=Nd and Dy, has been performed by vibrating sample magnetometry, ac susceptibility and x‐ray diffraction. The relationship between the magnetic properties and the layer thickness was studied systematically for X‐A Fe/Y‐A Dy, as the layer thicknesses X and Y were varied from 1.8 to 20 A. The ranges of layer thicknesses required for perpendicular anisotropy were determined. The interface and volume anisotropy energies were estimated for X‐A Fe/Y‐A Nd and the differences in the magnetic properties between X‐A Fe/7‐A Dy and X‐A Fe/7‐A Nd are discussed.

Kerr effect of two‐medium layered systems

Detailed and practical expressions are given for the magneto‐optical Kerr effect (MOKE) for various configurations of two media. One is a magneto‐optic (MO) one, and the other is a nonmagnetic (NM) medium. For a system of two thick media with a single interface, with a first‐order approximation in MOKE term Q, the Kerr function is determined by the product of a MOKE term Q and an optical term η. A second type of system includes a thin MO (or NM) layer deposited on a thick NM (or MO) substrate. For a MO/(NM‐substrate) configuration, the Kerr function is related to the Kerr effects from the air/MO and MO/NM interfaces, and to the Faraday effects of the MO layer, as well as to interference effects. The enhancement factor can be expected to be large by proper choice of materials. For a NM/(MO‐substrate) configuration, the total Kerr function is related to the Kerr effect from the NM/MO interface and can be enhanced by interference. The enhancement factor is expected to be less than one if the NM layer is stro...

Nanostructures of Sm-Co on Cr thin films

The nanostructures of Sm-Co on Cr thin films prepared by dc magnetron sputtering were investigated by high resolution transmission electron microscopy (HRTEM) and diffraction techniques. HRTEM micrographs show that the crystallites in the Sm-Co films, as revealed by the lattice fringes, are distributed discontinuously in the matrix. The matrix is amorphous as indicated by the microdiffraction study. The size of the crystallites is in the range of 2/spl sim/5 nanometers. The volume fraction of the crystallites in the film decreases from 91% to 54% as the argon pressure is increased from 5 mTorr to 30 mTorr. Micrographs recorded in a bright field transmission electron microscope (TEM) with a defocus of a few micrometers reveal grain-like structures of about 25 nm in some but not all films. This grain-structure is found to be inherited from the Cr underlayer. >

Magnetic switching volumes of CoSm thin films for high density longitudinal recording

For a high density recording media, the magnetic switching volume is of great importance when considering media noise and thermal stability. CoSm/Cr films have been prepared and the influence of the Cr underlayer thickness and of the magnetic layer preparation conditions on the magnetic switching volume have been investigated through magnetic viscosity and remnance curve measurements. The measured switching volumes ranged from 3.0 to 15.2/spl times/10/sup 18/ cm/sup 3/, and implications regarding noise and thermal stability are discussed.

Magnetism and anisotropy of Tb/Fe multilayers

Studies of the layer‐thickness dependence of hysteresis loops for Tb/Fe compositionally modulated films (CMF) are reported. The characteristics of magnetic properties, such as magnetization and uniaxial anisotropy, which depend on the FE layer thickness, can be interpreted in terms of the compositional dependence of magnetic properties of the constituent subnetworks and the spatial distribution of the constituent atoms. The magnetic properties of Tb/Fe CMF are analyzed with a micromagnetic model, and the behavior of the anisotropy and constituent magnetization near the compensation point is discussed.

Energy barrier and magnetic properties of exchange-coupled hard-soft bilayer

In this paper, the magnetic properties of an exchange-coupled hard-soft bilayer system have been analyzed based on its energy-barrier characteristics. Analytical solutions of the magnetic and structural parameters such as the energy barriers, the coercivities, the critical coupling-constant, the critical coupling dimension of soft phase, and the energy product have been derived. These analytical solutions reveal the correlation between the magnetic properties and the physical dimensions of its soft and hard phase constituents.