Scripta Metallurgica et Materialia最新文献

We have studied the possible spin modes in the 2D-honeycomb lattice using the two sub-lattices model.The stabilities of the modes obtained have been expressed in the form of inequalities in terms of exchange integrals. We have also obtained the propagation vectors suitable for the magnetizations which are compatible with the lattice structure. We have emphasized its properties in relation with 2D-hexagonal lattice.

Fe_{100 − x}B_x (with x = 20, 25 and 50) samples were prepared by high energy ball milling. The phase distribution, thermal stability, saturation magnetization and coercive force of these samples were examined by means of X-ray diffraction, differential scanning calorimetry and vibrating sample and extraction magnetometries, respectively. An excellent soft magnetic behavior, characterized by coercive forces of the order of 2.5 × 10⁻⁵ T, was detected in the case of the Fe₅₀B₅₀ samples milled during times from 150 up to 200 hours. This soft magnetic behavior was correlated to the presence of an amorphous phase in the as-milled sample with composition close to the nominal one.

CoCrPt(Ta,B) thin films with Cr underlayers were studied as potential candidates for ultra-high density magnetic recording media for data storage at 10 Gbits/inch². The experimental approach used was aimed at an analysis of the structure-properties relationships in these thin films. As a result structural and composition changes resulting in magnetic and noise properties have been identified. It has been shown that very high in-plane coercivities of 2700 Oe and above could be obtained in CoCrPt films with Pt contents < 20 at.%; in CoCrPtTa for Pt contents < 12% Pt (with 2.5–5% Ta) and in CoCrPtB (with 3–7% B) for Pt contents < 11%. Also methods for improvement of S^∗, noise characteristics and refinement of grain size and surface roughness have been demonstrated.

Since Co is ferromagnetic and Cr is not, compositional inhomogeneities are believed to play an important role in determining the magnetic and recording properties of Co-Cr based thin film magnetic recording media. By preferentially etching Co-enriched regions in a Co-Cr film we discovered a “Chrysanthemum-like Pattern”, suggesting the presence of very fine, periodic compositional variations within individual grains. Subsequent studies, including thermo-magnetic analysis, nuclear magnetic resonance and atom probe field ion microscopy revealed the existence of a Compositional Separation (CS) in these films, producing distinct Co-enriched and Cr-enriched compositional phases. More recently, neutron scattering experiments have provided evidence of a magnetic microstructure with features matching the scale of the Co-enriched regions. Further investigations of this phenomenon are expected to open up new areas of research in both magnetic recording and thin film metallurgy. We review our study of CS, explain control of the compositional distribution using film growth parameters and discuss possible origins of CS.

The tetragonal L1₀ family of ferromagnets including the Co-Pt, Fe-Pt, Fe-Pd and Mn-Al alloy systems exhibits high, uniaxial magnetocrystalline anisotropies with first anisotropy constants K₁ ~ 10⁷–10⁸ ergs/cm³. The domain parameters of these materials are similar to the rare earth permanent magnets and the defect structure is dominated by planar faults such as APB's, stacking faults, and twins. In this study the micromagnetic analysis of Kronmüller has been applied to elucidate the mechanism of coercivity controlling the hysteresis of the polytwinned L1₀ FePd equiatomic alloy and the results are consistent with pinning control involving atomically thick, planar defects. Also, Lorentz microscopy has been used to observe the interaction of magnetic domain walls with the planar faults characteristic of these materials. Finally, a thermomechanical treatment involving concomitant ordering and recrystallization is shown to eliminate the well-known polytwinned structures which generally evolve during the formation of the L1₀ phase leading to enhanced coercivities. The fundamental structure-property relationships involved are discussed.

Microstructures of high and low coercivity CoCrPt/Cr and CoCrPtTa/Cr were examined. High-coercivity samples were deposited either at high temperatures or with high substrate bias. Low-coercivity samples were deposited at room temperature and at low substrate bias. It was demonstrated that high coercivity films had significantly increased amount of planar faults compared to low-coercivity samples. The faults were identified as densely spaced stacking faults which apparently resulted from the film deformation either during or just after film deposition and they might contribute to higher coercivity due to local changes in crystal anisotropy. An increase in the amount of structural defects by either thermal or impact stress was associated in low-coercivity CoCrPt/Cr films with a profound change of magnetic properties.

We present magnetic characterization of epitaxial Fe/Cr(211) and Fe/Cr(100) superlattices grown simultaneously on MgO(110) and (100) substrates, respectively. At room temperature, the coupling for these two orientations oscillates in sign with the same period (18Å), phase and strength. These results indicate that the long-period oscillation is independent of the nested feature of the Cr Fermi-surface. We examine the temperature dependence of interlayer coupling and find a uniform AF bias develops in the (211) samples upon cooling and observe strongly temperature-dependent biquadratic coupling in the (100) samples.