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15 Dec 2007

Volume 102, Issue 12, Articles (12xxxx)

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An approach for researching uniaxial anisotropy magnet: Rotational magnetization

Xiaolong Fan, Desheng Xue, Changjun Jiang, Yu Gong, and Jinyun Li

J. Appl. Phys. 102, 123901 (2007); http://dx.doi.org/10.1063/1.2821729 (8 pages) | Cited 4 times

Online Publication Date: 17 December 2007

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In this study, rotational magnetization curves are used to investigate the anisotropy and the rotational magnetization process of uniaxial magnets. We measured the projection of magnetization as a function of angle between the magnetic field and the reference axis. The information about anisotropy, such as the directions of the easy axis and hard axis, as well as the anisotropy field Hk(i), is acquired. Simultaneously, the rotational magnetization reversal processes are derived. The Co and Fe28Co61Zr11 magnetic thin films with induced in-plane uniaxial anisotropy have been researched. We found that the rotational magnetization reversal process of the Co film is a coherent rotation. However, the Fe28Co61Zr11 film shows the similar behavior, except for a noncoherent rotation appearing when a small field parallels the hard axis.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
75.60.Jk Magnetization reversal mechanisms
75.50.Bb Fe and its alloys
75.50.Cc Other ferromagnetic metals and alloys

Enhanced magnetism in Fe-doped TiO2 anatase nanorods

Y. Ding, W.-Q. Han, and L. H. Lewis

J. Appl. Phys. 102, 123902 (2007); http://dx.doi.org/10.1063/1.2825043 (4 pages) | Cited 6 times

Online Publication Date: 18 December 2007

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Simultaneous high-Curie temperature (TC) ferromagnetism and enhanced temperature-independent paramagnetism (χTIP) is quantified in TiO2 anatase nanorods doped with nominal 0.5 at % Fe synthesized by a hydrothermal route. The nanorod dimensions are 8–35 nm in width and several hundred nanometers in length and possess an Fe concentration of 0.3–1.0 at %; no evidence of pure iron nanoparticles is detected. Magnetometry shows ferromagnetism at low fields that transitions to paramagnetism at higher fields with an enhanced temperature-independent susceptibility >100 times that of pure bulk anatase TiO2. The enhanced magnetism is tentatively attributed to the defect structure of the nanorods.
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75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.50.Dd Nonmetallic ferromagnetic materials
75.20.Ck Nonmetals
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Influence of the deposition-induced stress on the magnetic properties of magnetostrictive amorphous (Fe80Co20)80B20 multilayers with orthogonal anisotropy

Miguel González-Guerrero, José Luis Prieto, Pedro Sánchez, and Claudio Aroca

J. Appl. Phys. 102, 123903 (2007); http://dx.doi.org/10.1063/1.2822220 (4 pages) | Cited 4 times

Online Publication Date: 18 December 2007

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In this work, we experimentally justify that the control of the mechanical stress induced during the deposition of sputtered amorphous magnetostrictive (Fe80Co20)80B20 allows a custom design of its magnetic properties. FeCoB multilayers have been sputtered on thermal oxide Si substrates with different buffer materials. The crystalline quality and the thermomechanical properties of the buffer layer influence both the coercive and the anisotropy field. Those buffer layers with both high rigidity and poor thermal conductivity do not allow the dissipation of energy of the incoming sputtered material. Therefore, the mechanical stresses related to the deposition process cannot be released, leading to magnetic layers with high easy-axis coercive field and low anisotropy field. This shows that the mechanical stresses accumulated during deposition are a key parameter for the control of coercivity.
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75.80.+q Magnetomechanical effects, magnetostriction
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
68.60.Bs Mechanical and acoustical properties
81.15.Cd Deposition by sputtering
81.40.Gh Other heat and thermomechanical treatments
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Gw Magnetic anisotropy

Correlation of microstructure and magnetic properties for exchange-biased Co ferromagnets grown above and below the diluted antiferromagnet Co(Mg)O

Titus Leo, Jung-Il Hong, Ami E. Berkowitz, and David J. Smith

J. Appl. Phys. 102, 123904 (2007); http://dx.doi.org/10.1063/1.2821740 (5 pages) | Cited 1 time

Online Publication Date: 19 December 2007

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The microstructure of ferromagnetic/antiferromagnetic (FM/AFM) coupled bilayers consisting of 6 nm Co films, grown above and below 20 nm CoO layers diluted with nonmagnetic Mg, is correlated with measurements of exchange-bias field and coercivity as a function of Mg content. Increased Mg dilution is found to slightly decrease the grain width of the columnar oxide layers but no suggestion of Mg segregation at grain boundaries is detected using small-probe microanalysis. The order of growth and the amount of Mg dilution both play an important role in determining the size of the exchange bias field. The large increase in exchange coupling that is measured for Co-below bilayers is attributed to partial oxidation of the upper Co surface during initiation of the AFM deposition. The large decrease in coercivity measured for Co-above bilayers with high Mg dilution is closely correlated with the falloff in exchange-bias field. Overall, these results provide strong support for the uncompensated spin model of exchange bias.
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75.50.Cc Other ferromagnetic metals and alloys
75.50.Ee Antiferromagnetics
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
61.72.Mm Grain and twin boundaries

Structural, magnetic, and electric properties of Dy1−xSrxCoO3−δ (0.65 ≤ x ≤ 0.90)

A. Hassen, A. I. Ali, B. J. Kim, Y. S. Wu, S. H. Park, and Bog G. Kim

J. Appl. Phys. 102, 123905 (2007); http://dx.doi.org/10.1063/1.2822459 (7 pages) | Cited 1 time

Online Publication Date: 21 December 2007

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The structural, magnetic, and electric properties of Dy1−xSrxCoO3−δ perovskite have been investigated systematically over the range of doping, 0.65 ≤ x ≤ 0.90. The Rietveld refinements of x-ray powder diffraction patterns at room temperature indicate that the samples with 0.65 ≤ x ≤ 0.75 show a tetragonal structure with I4/mmm group symmetry, while the compounds with 0.80 ≤ x ≤ 0.90 are cubic with pm3m group symmetry. Zero field-cooled magnetization, M(T), of 0.65 ≤ x ≤ 0.85 samples reveals a cusp at around room temperature. For all samples, M(T) increases rapidly below 50 K due to the paramagnetism of Dy sublattice. The inverse magnetic susceptibility, χ−1(T), was described by using Curie–Weiss law. The resistivity (ρ) data can be explained according to a three-dimensional variable range hopping model in a certain temperature range. The density of states at the vicinity of Fermi level is roughly estimated.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.20.Ck Nonmetals
75.47.-m Magnetotransport phenomena; materials for magnetotransport
61.66.Fn Inorganic compounds

Magnetotransport properties of manganite based magnetic tunnel junctions

Yafeng Lu

J. Appl. Phys. 102, 123906 (2007); http://dx.doi.org/10.1063/1.2821399 (7 pages) | Cited 1 time

Online Publication Date: 27 December 2007

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We have studied spin-dependent tunneling in La2/3Ba1/3MnO3−δ based trilayer magnetic tunnel junctions fabricated by pulsed laser deposition. In the heteroepitaxial trilayer structures, a strained SrTiO3 layer of different thickness was used as a tunneling barrier. For the junctions with a SrTiO3 barrier, the measured tunneling characteristics deviated considerably from the ideal characteristics expected for elastic tunneling through an ideal barrier. The data indicate that inelastic multistep tunneling as described by the Glazman-Matveev model is present. Our analysis indicates that the SrTiO3 barrier layer consists of two different parts: The interface region with the manganite electrodes containing a high density of structural defects, and the central barrier layer with a small density of defects. The observed temperature dependence of the junction resistance can be explained by a series connection of the resistance contributions from the interfacial and central barrier part. The magnetic field dependence of the junction resistance is found to depend strongly on the barrier thickness and can show complicated behavior due to both a complex magnetic state in the junction electrode and magnetic interactions between the ferromagnetic electrodes. A very large tunneling magnetoresistance up to ΔR/Rp ≃ 1200% is observed that, however, depends sensitively on the magnetic history.
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75.47.Lx Magnetic oxides
75.45.+j Macroscopic quantum phenomena in magnetic systems
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Dd Nonmetallic ferromagnetic materials

Thermal hysteresis of interface biased ferromagnetic dots

Ana L. Dantas, A. S. W. T. Silva, G. O. G. Rebouças, A. S. Carriço, and R. E. Camley

J. Appl. Phys. 102, 123907 (2007); http://dx.doi.org/10.1063/1.2827478 (4 pages) | Cited 4 times

Online Publication Date: 27 December 2007

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We present a theoretical investigation of the thermal hysteresis of iron dots exchange-coupled to an antiferromagnetic substrate. We consider a temperature interval bounded by the Néel temperature of the substrate, and we calculate the heating and cooling curves in the presence of an external field oriented opposite to the interface exchange field. The thermal hysteresis is due to the temperature variation of the interface field and the influence of the geometrical shapes and sizes of the dots on the magnetic states and switching mechanisms. We show that Fe dots on an uncompensated NiO substrate exhibit large thermal hysteresis at room temperature, and external fields of a few kOe. The width of the hysteresis loops depends on the dimensions of the ferromagnetic dot, and can be significant for dots elongated in the direction of the interface field.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.30.Et Exchange and superexchange interactions
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)

Micromagnetic simulation of magnetization reversal process and stray field behavior in Fe thin film wire

Munekazu Ohno and Kanji Yoh

J. Appl. Phys. 102, 123908 (2007); http://dx.doi.org/10.1063/1.2821731 (9 pages) | Cited 1 time

Online Publication Date: 28 December 2007

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The magnetization reversal process of Fe thin film wire is studied based on two-dimensional micromagnetic simulation. It is demonstrated that the external field parallel to the width direction results in the formation of a 180° Néel wall, whereas the field applied to the thickness direction yields the Bloch-like walls, which turn into C-type walls in the residual state. These behaviors are explained by the anisotropic dependence of wall energy in the direction of the external field. The stray field during this process is analyzed in detail.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.60.Jk Magnetization reversal mechanisms
75.30.Gw Magnetic anisotropy
75.70.Ak Magnetic properties of monolayers and thin films

Magnetization reversal in Co/Pt multilayer with weak intergranular coupling

T. Wang, W. L. Pei, Y. Fu, T. Hasegawa, T. Washiya, H. Saito, S. Ishio, T. Wang, and F. S. Li

J. Appl. Phys. 102, 123909 (2007); http://dx.doi.org/10.1063/1.2817615 (4 pages)

Online Publication Date: 28 December 2007

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A [Co 0.4 nm/Pt 1 nm]8 multilayer with weak intergranular coupling was fabricated. The magnetization states after applying various negative fields along the easy axis were observed using a magnetic force microscope to reveal magnetization reversal behavior. Measurement results showed the magnetization reversal area separated into many small spots consisting of one or more grains. These spots reversed independently and the reversed spots did not expand at the boundary but remained stable while the negative magnetic field increased. A coherent rotation was further deduced by calculating the thermal activation volume by a dynamic coercivity method.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Jk Magnetization reversal mechanisms
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Vv High coercivity materials
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