Strong Uniaxial Magnetic Anisotropy Research Articles

First Principle Calculation of the Magnetocrystalline Anisotropy Energy of FePt and CoPt Ordered Alloys

The spin-polarized band calculations including spin-orbit interaction for L1 0 -FePt and CoPt ordered alloys have been performed with LMTO-ASA method in the frame of local spin density functional approximation. It has been shown that strong uniaxial magnetic anisotropy of both alloys is brought about by a large spin-orbit coupling of Pt atom and a strong hybridization of Pt d bands with highly polarized Fe (Co) d bands. The obtained magnetocrystalline anisotropy energy (MAE) is about 16×10 6 J/m 3 for FePt and 9×10 6 J/m 3 for CoPt. It is also found that both MAE's have a trend of increase with increasing axial ratio c / a in the vicinity of measured c / a . This can be regarded as being associated with the behavior that the MAE's decrease with increasing band filling.

Single Uranium-Site Properties of the Dilute Heavy Electron System UxTh1-xRu2Si2(x≤0.07)

Specific heat C , electrical resistivity ρ , magnetization M and magnetic susceptibility χ have been measured for the dilute tetragonal heavy-electron compounds U x Th 1- x Ru 2 Si 2 ( x ≤0.07), in the temperature range 100 mK≤ T ≤360 K and in the magnetic fields H up to 55 kOe. Non-Fermi-liquid behavior with unusual lnT dependence of C , ρ and χ has been observed at the low temperatures: as the temperature is lowered below about 10 K, C / T and χ increase logarithmically, and ρ decreases logarithmically. Systematical variations of these quantities with uranium concentration indicate that the observed non-Fermi-liquid behavior is ascribed to the properties of a single U ion embedded in the Th site of the ThRu 2 Si 2 metal. The magnetization curves M vs H / T indicate a strong uniaxial magnetic anisotropy along the tetragonal c -axis as well as a strong reduction of the 5 f moment of U ions. A possible interpretation based on the recent developments of the S =1/2 two-channel Kondo model is given.

Magnetic anisotropies of ultrathin Co films on Cu(001) and Cu(1113) substrates

We have determined the magnetic anisotropies of ultrathin Co layers on Cu(001) and Cu(1113) substrates using Brillouin light scattering and the magneto-optical Kerr effect. Experimental evidence was found that ferromagnetic order at room temperature in ultrathin epitaxial Co(001) layers on Cu(001) is stabilized by in-plane magnetic anisotropies. In the Co/Cu(1113) system we found a strong additional uniaxial in-plane magnetic anisotropy contribution of magnetoelastic origin with the easy axis parallel to the step edges.

ANOMALOUS MAGNETIZATION BEHAVIOUR IN U(Ru1-xRhx)Al

URuAl is a paramagnet with a susceptibility maximum around 50 K. The M(B) curve at 4.2 K displays a broad S-shape with a susceptibility maximum around 30 T. These features can be related to magnetic fluctuation effects. Substitution of Ru by Rh leads to a gradual suppression of the M(B) anomalies (and to the onset of ferromagnetism at x≃0.2) which, however, survive even in the ferromagnetic regime. Because of the strong uniaxial magnetic anisotropy, these phenomena are observed only along the c-axis.

Microstructure and magnetic anisotropy of ultrathin Co/Pt multilayers grown on GaAs (1̄1̄1̄) by molecular-beam epitaxy

Multilayers of (Co3 Å, Pt15 Å)x, x=15 or 30 repeats, with or without a 200 Å silver buffer layer, were grown on GaAs (111) substrates by molecular-beam epitaxy. Vibrating sample magnetometry measurements confirmed that the samples with the Ag buffer layer show strong uniaxial magnetic anisotropy perpendicular to the surface. The perpendicular anisotropy exhibited by these metallic superlattices is discussed in terms of the microstructure of the overall multilayer stack, as well as the structural characteristics of the Co interface layer. Samples grown on the Ag buffer layer show strong (111) texture with 30–40-nm-size twin-related grains. These grains, correspond to the two possible (111) stacking sequence for an fcc lattice, i.e., double positioning. However, direct growth on GaAs (111) results in randomly oriented 10–20 nm grains. All samples exhibit a repeat period of 1.83 nm in both low-angle reflectivity and high-angle Θ–2Θ x-ray scattering measurements. In addition, transverse scans through the low-angle multilayer Bragg peaks show the interfaces to be diffuse in nature indicative of considerable in-plane inhomogeneity and/or compound formation. High-resolution electron microscopy measurements of cross sections compared with image simulations confirm that the interface layer is diffuse and its stoichiometry is such that the Co occupation is less than 40%. Redistribution of Co should then extend over at least four monolayers. The nanostructure of the samples grown with the Ag buffer layer comprises an eight atomic layer repeat with the Co interface layer diffuse over four monolayers. The microstructure is strongly (111) textured with columns of twin related 30-nm-sized grains. It is suggested that the combination of interdiffusion, highly oriented but twin-related columnar growth, small grain size with a possible nanometer-scale second phase may be the key to the understanding of the perpendicular anisotropy observed in these (111) superlattices.

Giant magnetoresistance effects in UNiGa

Magnetic transitions in UNiGa were found to cause pronounced anomalies in temperature and magnetic-field dependencies of the electrical resistivity. The resistivity values are drastically reduced by the field induced transition from an antiferromagnetic to a ferromagnetic phase. The giant magnetoresistance (as large as Δρ/ρ=−87% at T=1.2 K for i∥c) observed in UNiGa is typical for materials characterized by a strong coupling of conduction electrons with highly correlated f electrons. The observed anisotropy of transport properties is closely connected with the strong uniaxial magnetic anisotropy of this compound.

Magnetic anisotropies in ultrathin fcc Fe(001) films grown on Cu(001) substrates

Brillouin light scattering and ferromagnetic resonance have been used to measure the magnetic-field dependence of the magnon frequency at room temperature for three- monolayer-thick films of fcc Fe(001) grown by means of molecular-beam epitaxy on Cu(001) substrates. These films exhibit a strong uniaxial magnetic anisotropy which causes the magnetization to be oriented perpendicular to the film plane in zero applied field. Four specimens were grown on copper substrates prepared using a chemical polishing technique which avoided the use of abrasives: This treatment greatly reduced the density of etch pits on the copper surface. The uniaxial anisotropies found for these specimens were very consistent and comparable to that previously measured for the best film grown on a mechanically polished copper substrate. There is evidence that substrate smoothness is improved and, hence, that the uniaxial anisotropy is increased when the substrate is covered with a few monolayers of epitaxial copper before the iron films are grown.

Flux growth and magnetic properties of hexagonal ferrite single crystal (abstract)

Using a new tenary system flux Bi2O3-BaO-B2O3, the growth of hexagonal ferrite single-crystal BaM and ZnW has been investigated. The flux has a lower melting point and wider growth temperature range. The shape characteristic of the crystals grown has changed from thin platelets to columns. The substitution of diamagnetic ions in hexagonal ferrite has been studied. In order to discuss the origin of magnetic anisotropy in hexagonal ferrites BaM and ZnW, the magnetic anisotropy at each sublattice has been calculated by a well-known H. B. Callen and E. Callen anisotropy model which is given by K1(T)/K1(0) =I1+1/2[Zi(T)]/I1/2[Zi(T)] with Zi(T)=2KT∑nm=1N imSiSmJimσm(T). The magnetization σi(T) and the exchange parameters Jim in different sublattice has been fitted by a least-squares method to the experimental values of the saturation magnetization, according to the molecular field theory. The results show that the contributions of Fe3+ in different sublattices to magnetic anisotropy are different. The strong uniaxial magnetic anisotropy in hexagonal ferrites is attributed mainly to the contribution of ferric ions located in trigonal bipyramidal sublattices 2b BaM and 2b 2b in ZnW. The influence of diamagnetic ions Zn, In, Al substitution for Fe3+ to magnetic anisotropy can be explained by the calculated resultant.

Mössbauer and X-ray diffraction studies of amorphous Fe-Ni alloy films deposited by DC sputtering

The analysis of the Mössbauer spectra reveals that the amorphous Fe-Ni alloy films without metalloid produced by dc sputtering have strong uniaxial magnetic anisotropy perpendicular to the film plane and the hyperfine field in the amorphous state is larger than that in the crystalline state in Invar composition.

冷間加工を施したFe-Cu-Mn系合金の磁気的性質

Magnetic properties of Fe-Cu-Mn ternary alloys of 45 Fe-Cu-Mn and 80 Fe-Cu-Mn were investigated. Additions of less than 3 wt% manganese did not change the dendritic structures of Fe-Cu alloys, retaining their good workability. The addition of manganese to Fe-Cu binary alloys improved the coercivity, squareness and residual induction even with a low degree of cold reduction. The heat-treatment at 350∼500°C after the cold-reduction was necessary to obtain such high values of magnetic properties as Br 15.5 kG, Hc 55 Oe and Br⁄B100≥0.96 for 80 Fe-1.7 Mn-Cu alloy, and Br 7.5 kG, Hc 350 Oe for 45 Fe-1.8 Mn-Cu alloy.Magnetic torque measurments indicated that the improvement of squareness by heat-treatment was due to a strong uniaxial magnetic anisotropy which was induced by the application of cold-reduction and subsequent heat treatment. The values of coercivity and residual induction (Br) were changed by a combined effect of heating time (t) and heating temperature (T), obeying the following equations: Hc∝−logt and Hc∝exp(±E⁄RT), respectively. These equations are very convenient to control the magnetic properties of Fe-Cu-Mn ternary alloys.