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A study is conducted on the film growth of fully chemically ordered FePt (001) epitaxial thin films. Results show that these films have high degree of expitaxy and chemical ordering. Highly interconnected magnetic stripe domains with magnetization perpendicular to the film were found in films thicker than 50nm, which lead to characteristic low remanence magnetization curves. Two mechanisms that lead to irregular domain patterns and high remanence and coercivity in the polar hysteresis loops are also determined.

Interest in the magnetic properties of the ordered equiatomic alloy FeRh has been revived in recent years due to potential applications in heat assisted magnetic recording. This is based on the existence of a first order hysteretic phase transition from strongly anisotropic antiferromagnet (AF) to relatively isotropic ferromagnet (F) upon warming to ∼370 K. Here we investigate this transition, which shows significant coupling between structural, magnetic, and electronic degrees of freedom, via wide temperature range magnetotransport and magnetometry measurements on ordered epitaxial MgO(001)/FeRh(1000 Å) films. Consistent with bulk measurements, a large decrease in resistivity (∼30%) occurs on warming through the transition. The transition temperature shifts with applied magnetic field at -0.75 K/kOe due to the field-induced stabilization of the F phase, leading to large negative magnetoresistance (∼40% in 90 kOe) in the transition region (340-400 K). Isothermal field cycles reveal consistent behavior where the resistivity is controlled by the magnetization changes as the AF/F phase boundary is crossed. In the F state at high temperature anisotropic magnetoresistance (AMR) is observed (maximum amplitude ∼0.45%), in addition to high field negative MR due to field-induced suppression of electron-magnon scattering. The temperature dependence of the AMR reveals clear two-phase coexistence in the hysteresis region, providing a sensitive probe of remnant F regions upon cooling through the transition. This behavior, and the accompanying coercivity enhancement, is discussed in terms of possible two-phase microstructures across the magnetic phase transformation. [ABSTRACT FROM AUTHOR]

Two series of epitaxial CoPt and FePt films, with nominal thicknesses of 42 or 50 nm, were prepared by sputtering onto single-crystal MgO(001) substrates in order to investigate the chemical ordering and the resultant magnetic properties as a function of alloy composition. In the first series, the film composition was kept constant, while the substrate temperature was increased from 144 to 704 °C. In the second series the substrate temperature was kept constant at 704 °C for CoPt and 620 °C for FePt, while the alloy stoichiometry was varied in the nominal range of 40–60-at. % Co(Fe). Film compositions and thicknesses were measured via Rutherford backscattering spectrometry. The lattice and long-range order parameter for the L10 phase were obtained for both sets of films using x-ray diffraction. The room-temperature magnetocrystalline anisotropy constants were determined for a subset of the films using torque magnetometry. The order parameter was found to increase with increasing temperature, with ordering occurring more readily in FePt when compared with CoPt. A perpendicular anisotropy developed in CoPt for substrate temperatures above 534 °C and in FePt above 321 °C. The structure and width of the magnetic domains in CoPt and FePt, as seen by magnetic force microscopy, also demonstrated an increase in magnetic anisotropy with increasing temperature. For the films deposited at the highest temperatures (704 °C for CoPt and 620 °C for FePt), the order parameter reached a maximum near the equiatomic composition, whereas the magnetocrystalline anisotropy increased as the concentration of Co or Fe was increased from below to slightly above the equiatomic composition. It is concluded that nonstoichiometric L10 CoPt and FePt, with a slight excess of Co or Fe, are preferable for applications requiring the highest anisotropies. [ABSTRACT FROM AUTHOR]

We have produced assemblies of monodisperse 4 nm FePt nanoparticles using polymer-mediated layer-by-layer deposition at room temperature. The process leads to good control of particle assembly thickness and offers great potential for future fabrication of ultra-high density magnetic storage media. Vibrating sample magnetometry with fields up to 9 T was applied to study the magnetic properties of the particle assemblies as a function of annealing condition while near edge x-ray absorption fine structure (NEXAFS) spectroscopy and x-ray diffraction (XRD) were used to investigate the chemical nature and structural properties within particles. It was found that the coercivity can be as high as 22.7 kOe for samples annealed at 800 °C, the moment density (normalized to the particle volume) for the sample annealed at 650 °C is estimated close to the value for bulk FePt, at 1140 emu/cm[SUP3]. NEXAFS spectroscopy shows that the Fe in the as-deposited assemblies is partly oxidized, and the oxidation is greatly reduced by annealing. XRD studies on the assemblies annealed at high temperature revealed the increased atomic order and the formation of the high-anisotropy L1[SUB0] phase within the particles. However, the high-temperature annealing also resulted in nanoparticle agglomeration. [ABSTRACT FROM AUTHOR]

Magnetic media using materials with high uniaxial magneto-crystalline anisotropy, K[sub u], combined with a thermal assist to overcome write field limitations have been proposed as one of the potential technologies to extend the areal density of magnetic disk recording beyond the limitations of current technology. Here we present an investigation on structural and temperature dependent magnetic properties of chemically ordered epitaxial Fe[sub 55-x]Ni[sub x]Pt[sub 45] thin films. Increasing Ni additions result in a steady reduction of magneto-crystalline anisotropy, saturation magnetization, and Curie temperature. The ability to control thermomagnetic properties over a wide range makes Fe[sub 55-x]Ni[sub x]Pt[sub 45] and similar FePt-based pseudo-binary alloys attractive base materials for media applications in thermally assisted magnetic recording. [ABSTRACT FROM AUTHOR]

Focuses on a study of interface reactions between the magnetic layer and the protective carbon coating, and the influence of these interactions on magnetic properties of rigid disk media for magnetic data storage. Background of the study; Experimental details; Results of the study.

Two series of epitaxial CoPt and FePt films, with nominal thicknesses of 42 or 50 nm, were prepared by sputtering onto single-crystal MgO(001) substrates in order to investigate the chemical ordering and the resultant magnetic properties as a function of alloy composition. Conclusion reveals that nonstoichiometric L1(sub 0) CoPt and FePt, with a slight excess of Co or Fe, are preferable for applications requiring the highest anisotropies.

The onset of chemical ordering due to annealing of FePt nanoparticle assemblies is discussed. It is found that much of the Fe in the as-synthesized particles is partially oxidized, and the degree of oxidation is chemically reduced with increasing annealing temperature.

The growth temperature is one of the critical parameters in the formation of the chemically ordered L1[sub 0] phase in FePt. To uniquely determine the influence of growth temperature, while other growth parameters remain fixed, we present the “temperature wedge method” where a calibrated temperature gradient of several hundred Kelvin is established across the substrate during co-deposition of Fe and Pt. Samples were deposited in a temperature range of 250 °C–600 °C simultaneously on MgO(001) and MgO(110) substrates. The Fe[sub approx. 50]Pt[sub approx. 50] composition was verified by Rutherford backscattering. The chemical order parameter, S, at different positions along the samples, i.e., at different growth temperatures, was determined by x-ray diffraction measurements, and it was found that at all temperatures S(001)>S(110). Perpendicular and in-plane magneto-optic Kerr hysteresis loop measurements indicate large magnetic anisotropy at the “hot ends” of the samples, corresponding to large values of S. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]