Bao-Shan Han

On annealing-induced amorphization and anisotropy in a ferromagnetic Fe-based film: A magnetic and property study

Magnetic and property characteristics of sputtered Fe65Ti13Co8Ni7B6Nb1 film in as-deposited and annealed conditions are examined. The film is transformed into various nanoscale and amorphous structures during annealing. Fully amorphous structure is obtained at 773–823K, whereas nanocrystalline γ-fcc FeNi, cubic Fe(Ni) and FeNi phases evolve sequentially at various temperatures. Amorphization and nanocrystallization yield alterations in electrical, hardness and magnetic properties with good soft magnetic properties obtained at 898K. Magnetic force images reveal stripe magnetic domain structures at 923–973K, indicating the presence of the strong stress-induced perpendicular magnetic anisotropy due to the combined effect of the positive magnetostriction and the compressive stress.

Domain structure in Fe-implanted Nd2Fe14B magnets

The surface microstructure of Nd2Fe14B magnets was modified by Fe ion implantation. Their domain structures were studied by magnetic force microscopy. Corrugation and spike pattern domains were found on the (001) plane of unimplanted Nd2Fe14B. After implantation, a domain structure transition from complex maze to stripe pattern was found. The width of the stripe domain increases with increasing Fe dose. It indicates that the magnetic moments in the implanted layer turn out of their easy axis. The magnetization configurations in the implanted magnets were calculated using a micromagnetics method. The theoretical results agree well with the experimental results.

Effect of CrW underlayer on structural and magnetic properties of FePt thin films

L10 ordered FePt thin films with face-centered-tetragonal (001) texture have been prepared by magnetron sputtering on Cr100−xWx underlayer. The dependence of Cr100−xWx microstructure and FePt texture on the W content in the Cr underlayer was investigated. The addition of W element in Cr underlayer enhances the Cr (200) texture and increases the lattice constant of Cr, which is favorable for lowering the transformation temperature from fcc to fct phase because of the increase of the tensile stress along the FePt a axis. A good FePt (001) texture is obtained on the Cr85W15 underlayer with a substrate temperature of 400°C. The coercivity of FePt thin films on CrW underlayer is higher than on Cr underlayer and increases with increasing W content in the Cr underlayer because the formation of the CrW alloy inhibits the diffusion between FePt and CrW layer. A 5nm Pt intermediate layer was employed to suppress the diffusion between FePt and CrW underlayer further.

Hard magnetic properties in isotropic nanocomposite Pr2Fe14B/α-Fe ribbons

Abstract We have studied the demagnetization behavior for melt-spun nanocomposite Pr 8 Fe 87 B 5 ribbons in this paper. We have defined H ex which reflects the magnetic hardening of α-Fe and H irr which expresses the irreversible reversal of magnetic hard phase. It is found that magnetization behavior can be well described using H ex and H irr . A magnetic single-phase behavior is observed as H irr approximately equals to H ex . Remanence enhancement is not only determined by the intergrain exchange coupling but also dominated by the anisotropy of Pr 2 Fe 14 B phase. To achieve a high energy product (BH) max , the ideal microstructure is discussed. The magnetic reversal in the ribbons is mainly controlled by inhomogeneous pinning of nucleated type.

Co∕Pt multilayers with large coercivity and small grains

Multilayers of [Co∕Pt]20, with tCo∕tPt≐7 and the period Λ in the range of 0.27–0.69nm, and [Co(0.46nm)∕Pt(0.07–0.14nm)]20 have been prepared by sputtering at low deposition rates and a high Ar pressure of 7.8Pa. Structure and magnetic properties were characterized by x-ray diffraction, transmission electron microscopy, magnetometry measurements, and magnetic force microscopy. Column structure, coherent stacking of Co and Pt layers, and small grains have been observed. The average atomic interplane distance d111 changes with the constituent layer thickness. In the first series of Co∕Pt multilayers, the out-of-plane coercivity gradually increases to reach a maximum, with the bilayer period increasing from 0to0.58nm, and decreases with further increasing period. For the second series, the out-of-plane coercivity increases to reach a maximum of 6.5kOe with tPt increasing from 0.07to0.13nm and decreases with further increasing tPt. In order to explain the strong magnetic perpendicular anisotropy, the magnetoel...

Perpendicular magnetic anisotropy of La0.67Sr0.33MnO3 thin films grown on CaMnO3 buffered SrTiO3

La0.67Sr0.33MnO3(LSMO) thin films were grown onto CaMnO3(CMO) buffered SrTiO3(100) by pulsed laser deposition. Because of the in-plane compressive strain induced by the lattice mismatch between CMO and LSMO, a perpendicular magnetic anisotropy (PMA) was obtained in the overlayer LSMO. Using the magnetic force microscopy, stripe magnetic domains in association with the PMA were observed at room temperature. Furthermore, the magnetoresistance with in-plane magnetic field parallel and vertical to the measuring current was studied at 5 and 300 K, and its correlation with the magnetic anisotropy has been discussed.

Direct observation of phase separation in La0.45Sr0.55MnO3−δ

We provide evidence of phase separation in La0.45Sr0.55MnO3−δ using electron spin resonance, magnetic force microscopy (MFM), x-ray diffraction, and magnetic and transport measurements. The results reveal that ferromagnetic and antiferromagnetic phase coexist at low temperature and that ferromagnetic and paramagnetic phases coexist in the temperature range between the Neel and the Curie temperature. Moreover, the size and shape of ferromagnetic phase (the minority phase) in the sample were observed directly by MFM. From these results, we infer an electroneutral type phase separation, possibly resulting from a nonuniform distribution of oxygen vacancies, as opposed to charge segregation.

Honeycomb domain structures in amorphous TbFe thin films

The magnetic properties and domain structure of amorphous TbFe thin films were studied by magnetic measurement and magnetic force microscope. Honeycomb domain structures were found in the as-deposited amorphous film. The domain structures were composed of many small white round dots embedded in the black matrix, which formed an irregular hexagonal pattern with some deformation. The average dot size was about 450 nm, with an average separation of 610 nm. The derived domain wall energy density γ and the exchange constant A were 0.95×10−2 and 1.79×10−11 J/m, respectively.The magnetic properties and domain structure of amorphous TbFe thin films were studied by magnetic measurement and magnetic force microscope. Honeycomb domain structures were found in the as-deposited amorphous film. The domain structures were composed of many small white round dots embedded in the black matrix, which formed an irregular hexagonal pattern with some deformation. The average dot size was about 450 nm, with an average separation of 610 nm. The derived domain wall energy density γ and the exchange constant A were 0.95×10−2 and 1.79×10−11 J/m, respectively.

Magnetic properties and magnetic-domain structures of nanocrystalline Sm2Fe14.5Cu0.5Ga2Cy

The magnetic properties and magnetic-domain structures of nanocrystalline Sm2Fe14.5Cu0.5Ga2Cy (y=0–2.0) alloys prepared by melt spinning and subsequent heat treatment were studied. The coercivity of optimum annealing ribbons first increases significantly with increasing carbon content for y⩽1.0. It does not change much for 1<y⩽2. The maximum coercivity μ0Hc is 2.6 T at room temperature for ribbons with y=1.5–2.0 after annealing in a Sm atmosphere at 1047 K for 30 min. The domain structure was studied by magnetic-force microscope. The as-spun amorphous Sm2Fe14.5Cu0.5Ga2C1.5 ribbons exhibit very weak magnetic contrast. The magnetic-domain length scale is 300–700 nm and much larger than the grain size in the Sm2Fe14.5Cu0.5Ga2C1.5 ribbons, which may be caused by interactions between the grains. In the Sm2Fe14.5Cu0.5Ga2 ribbons, the domain-length scale is 100–200 nm and the magnetic-tip–sample interaction strength is weaker than in the Sm2Fe14.5Cu0.5Ga2C1.5 ribbons. These results have been correlated with the ...

Magnetic Force Microscopy Study of CoPtCrO Perpendicular Media With Superparamagnetic And Permanent Magnet Tips

This paper compares the images obtained by superparamagnetic and permanent magnetic force microscopy (MFM) tips, that allows us to explain the issues related to the frequency double in some of domain images of the recording media. This paper also investigates the domain structures of high density recording bits (up to 1100 kfci) written on ac and dc-erased CoPtCrO perpendicular magnetic recording (PMR) media with permanent magnet MFM tips under ambient conditions.