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Spin-dependent transport property through molecules is investigated using a monolayer of oleic acid molecule self-assembled half metallic La 0.7 Sr 0.3 MnO 3 (LSMO) nanoparticles, which was synthesized using a coprecipitation method. Fourier transform infrared spectroscopy was used to confirm that one-monolayer oleic acid molecules chemically bond to the LSMO nanoparticles. The transport properties and magnetoresistance (MR) effect of the oleic acid molecule coated LSMO nanoparticles were measured by a direct current four probes method using a Cu/nanoparticle assembly/elargol electrode sandwich device with various temperatures and bias voltages. The non-linear I – V curve indicates a tunneling type transport properties. The tunnel barrier height around 1.3 ± 0.15 eV was obtained by fitting the I – V curve according to the Simmons equation. The magnetoresistance curves can be divided to high-field MR and low-field MR (LFMR) parts. The former is ascribed to the influence of spin disorder or canting within the LSMO nanoparticle surface and the latter one with strong bias dependence is attributed to the spin-dependent tunneling effect through the insulating surface layer of LSMO and oleic acid molecules. The enhanced LFMR effect for oleic acid coated LSMO with respect to the bare LSMO was attributed to the enhanced tunneling transport and weak spin scattering in oleic acid molecule barrier.

National Basic Research Program of China [2012CB933103]; National Natural Science Foundation of China [51171158, 50971108, 50825101]; Fundamental Research Funds for the Central Universities of China [201212G001]

It is important to control magnetic anisotropy of ferromagnetic materials. In this work, FeCo thin films are deposited on the curving substrates by electrochemical deposition to adjust the stress-induced magnetic anisotropy. The compressive stress is produced in the as-deposited films after the substrates are flattened. A simplified theoretical model of ferromagnetic resonance is utilized to measure the intrinsic magnetic anisotropy field and saturation magnetization. The results show that the stress-induced magnetic anisotropy and the resonance frequency increase with the increase of substrate curvature. The induced easy axis is perpendicular to the compressive stress direction.

FeCoNd thin film with thickness of 166 nm has been fabricated on silicon (1 1 1) substrates by magnetron co-sputtering and annealed for one hour under magnetic field at different temperatures (Ta) from 200 °C to 700 °C. The As-deposited and annealed FeCoNd film samples at Ta ≤ 500 °C were amorphous while the ones obtained at Ta ≥ 600 °C were crystallized. We found that the perpendicular anisotropy field gradually decreases as the annealing temperature increases from room temperature to 300 °C. A well induced in-plane uniaxial anisotropy is achieved at the annealing temperature between 400 and 600 °C. The variation of the dynamic magnetic properties of annealed FeCoNd films can be well explained by the Landau–Lifshitz equation with the variation of the anisotropy field re-distribution and the damping constant upon magnetic annealing. The magnetic annealing might be a powerful post treatment method for high frequency application of magnetic thin films.

The magnetic properties of FeNiSm thin films with different thicknesses, different Ta interlayer thicknesses and different numbers of Ta interlayers were investigated. The single layer FeNiSm shows in-plane uniaxial anisotropy at a thickness below critical value, but shows weak perpendicular anisotropy with a stripe domain structure at thickness above the critical value. Experiments indicate that one or more Ta interlayers inserted into thick FeNiSm films with weak perpendicular anisotropy were effective not only in canceling the perpendicular anisotropy, but also in recovering the in-plane uniaxial anisotropy. Blocking of the columnar growth of FeNi grains by the Ta interlayer is considered to be responsible for this spin reorientation phenomenon. Moreover, the magnetization reversal mechanism in FeNiSm films with uniaxial anisotropy can be ascribed to coherent rotation when the applied field is close to the hard axis and to domain-wall unpinning when the applied field is close to the easy axis. The dynamic magnetic properties of FeNiSm films with uniaxial anisotropy were investigated in the frequency range 0.1–5 GHz. The degradation of the soft magnetic properties of magnetic thin films due to the growth of columnar grains can be avoided by insertion of a Ta interlayer.

The magnetic FeCoNd films with thickness ( t) from 50 to 166 nm were fabricated by RF magnetron co-sputtering at ambient condition. The amorphous structures of all of the films were investigated by X-ray diffraction and transmission electron microscopy. A spin reorientation transition from in-plane single domain state to out-of-plane stripe domain state was observed as a function of t. When t is below a critical thickness, magnetic moments lie in the film plane corresponding to in-plane single domain state because of the strong demagnetization energy. However, when t is increased, out-of-plane stripe domain structure was developed due to a dominated perpendicular magnetic anisotropy. Scanning electron microscopy data indicate that the perpendicular anisotropy, which is responsible for the formation of stripe domains, may result from the shape effect of the columnar growth of the FeCo grains.

We present a method for calculating demagnetization interaction in micromagnetic simulations for two-dimensional periodic boundary conditions without any range cutoff. The method was implemented in a full micromagnetic package by recombining the demagnetization tensors in real space which need to be computed only once at the beginning of the simulations. The errors of redefined demagnetization tensors are approximated allowing to estimate the accuracy of final results.

CoFe 2 O 4 nanowire arrays were fabricated by electrodeposition of Fe 2+ and Co 2+ into anodic aluminum oxide (AAO) templates and further oxidization. The phase structure of the nanowires is cubic spinel-type, and the XRD result exhibits perfect preferred crystallite orientation along the nanowire axes. Compared with CoFe 2 O 4 nanowire arrays synthesized by other methods, the magnetic hysteresis loops demonstrate that the arrays of nanowires exhibit uniaxial magnetic anisotropy with easy magnetization direction along the nanowire axes owing to the large shape anisotropy. This approach provides a facile technology to fabricate oxide nanowires with uniaxial magnetic anisotropy.

Arrays of Fe 61 Co 27 P 12 nanowire with an aspect ratio about 70 were prepared in anodic aluminum oxide templates by electrodeposition. The influences of annealing temperature on structure and magnetic properties of Fe 61 Co 27 P 12 nanowires were studied. When the specimens were annealed below 400 °C, there are no obvious changes in structure except relaxation. With the annealing temperature increasing from 400 to 600 °C, the Fe–Co phase is detected by X-ray diffraction and Mossbauer spectra. The crystalline fraction and hyperfine field can be derived from Mossbauer spectra. The room temperature magnetic hysteresis loops show that the coercivity and squareness of the nanowire arrays in parallel to the wire axis increase with the increasing of annealing temperature, which mainly attributes to the strengthening of anisotropy.

β-FeOOH nanowire arrays were assembled into porous anodized aluminum oxide (AAO) templates by electrochemical deposition in the mixture solution of FeCl 3 and (NH 4 ) 2 C 2 O 4 . In order to obtain well-crystallized α-Fe 2 O 3 and other iron oxides nanowires, β-FeOOH nanowire arrays with amorphous crystal structure were heat-treated at different temperatures from 200 to 600 °C. The decomposition products were characterized by DTA, XRD, FTIR, and Mossbauer spectroscopy. When heat-treated at 200 °C, only 65% of β-FeOOH decomposed, whereas, when the temperature was up to 300 °C, it was completely decomposed and formed poorly crystallized β-Fe 2 O 3 . This transition temperature is higher than the 200 °C obtained on other β-FeOOH materials. However, when heated above 300 °C, the main products are characterized as poorly crystallized α-Fe 2 O 3 nanowires, whereas, well-crystallized α-Fe 2 O 3 nanowire arrays can be formed when the temperature was up to 600 °C, and this temperature is also higher compared with those temperatures observed on other β-FeOOH materials. From Mossbauer results, the α-Fe 2 O 3 nanowires were composed of fine particles in which 66% of the particles are superparamagnetic.

Arrays of Fe 0.88− x Co x P 0.12 amorphous nanowires were fabricated by electrochemical deposition. Transmission electron microscope result shows that the nanowires are regular and uniform, about 2.8 μm in length and 40 nm in diameter. Selected area electron diffraction and X-ray diffraction results indicate that the nanowires are amorphous in structure. Vibrating sample magnetometer and Mossbauer spectrometer are employed to study the magnetic properties of nanowire arrays at room temperature. The results show that the arrays of nanowires exhibit uniaxial magnetic anisotropy that depends on the shape of each individual nanowire. When the applied magnetic field is parallel to the wire axis, the coercivity and squareness of the nanowire arrays increase with increasing Co concentration. The magnetic moments of the Fe atoms are approximately parallel to the wire axis and the hyperfine field decreases with increasing Co content.

For the first time, the photoluminescence (PL) spectra of porous anodized aluminum oxide (AAO) films impregnated with essentially non-fluorescent 3, 5, 7, 2′, 4′-pentahydroxyflavone (morin) and morin–human immunoglobulin (IgG) were investigated and compared with those of liquid solutions. It was found that their PL band positions are similar to that of morin–Al3+ in ethanol solution, and the PL intensity of embedded morin alone can be enhanced greatly by the introduction of human immunoglobulin. We infer that the appearance of the PL band detected here is due to the formation of morin–Al complex in the holes of AAO with the inner wall involved, and a likely luminescent mechanism is proposed to elucidate the PL enhancement phenomena due to the coexistence of morin and IgG in the AAO pores, which is confirmed by ultraviolet (UV)–visible and Fourier transform infrared (FTIR) measurements. Moreover, it is also found that the PL intensity increases with the pore size.

Nanowire arrays of the alloy, Fe 0.68 Ni 0.32 , with different nanowire diameters have been fabricated by the electrochemical deposition method. X-ray diffraction and Mossbauer spectroscopy were employed to characterize the size effect on the structure and micro-magnetic properties of the nanowire array, respectively. The Fe 0.68 Ni 0.32 arrays with different diameters are stabilized in a BCC structure with a [1 1 0] texture oriented along the long axis of the nanowires. The Mossbauer spectra of the nanowire arrays with smaller diameters show an absence of the second and fifth peaks, which then emerge with increasing diameter. The size effects on the hyperfine parameters are discussed.

For the first time, the photoluminescence (PL) spectra of anodic porous alumina (P-Al) films impregnated with essentially non-fluorescent morin and morin–trypsin (Try) were investigated and compared with those of liquid solutions. It was found that their PL positions are similar to that of dye–Al3+ in ethanol solution, and the PL intensity of embedded dye–Try is much higher than that of embedded dye alone. We infer that the appearance of the PL band detected here is due to the formation of morin–Al complex in the holes of P-Al with the inner wall involved, and a likely luminescent mechanism is proposed to elucidate the PL enhancement phenomena due to the coexistence of morin and Try in the P-Al pores, which is confirmed by UV and FTIR measurements. Moreover, it is also found that the PL intensity increases with the pore size.

Using electrochemical deposition, 4 μm long Fe0.68Ni0.32 alloy nanowire arrays with diameters in the range of 16–100 nm are fabricated in porous anodic alumina films. The results indicate that all of the Fe0.68Ni0.32 alloy nanowire arrays with different diameters are stabilized in a BCC structure with a [1 1 0] texture oriented along the long axis of the nanowires. For the whole diameter range of the nanowires, the easy magnetization axis is parallel to the nanowire long axis. With increasing diameter, the coercivities obtained both in parallel and perpendicular directions decrease. For nanowire arrays with larger diameters, the coercivity has a maximum when the applied field is perpendicular to the long axis of the nanowires, which is different from the results for nanowire arrays with smaller diameters. This different coercivity behaviour is discussed by considering the shape anisotropy, magnetocrystalline anisotropy and the dipolar interaction between the nanowires.

The structure and magnetic properties of γ′-(Fe 1− x Sn x ) 4 N samples have been studied using X-ray diffraction and 57 Fe Mossbauer spectroscopy. It has been shown that the single-phase (Fe 1− x Sn x ) 4 N compounds can be prepared in the composition range of 0.0⩽ x ⩽0.3, which have the similar structure as γ′-Fe 4 N The lattice parameter with the increase of Sn concentration can be well fitted with two linear relationships a 0 ( x )=3.795+0.019 x (with x ⩽0.10 ) and a 0 ( x )=3.797+0.228( x −0.10) (with 0.1⩽ x ⩽ 0.3). The fitting results of Mossbauer spectra indicate that the hyperfine parameters have the same changing tendency with lattice parameter, and the Sn atoms have a preference to be located at the corner site.

Co 100− x Sn x alloy nanowires were fabricated by electrodeposition of Co 2+ and Sn 2+ into anodic aluminum oxide (AAO) templates. X-ray diffraction results indicate that the crystal structures of the nanowires changed from polycrystal to amorphism, and then to polycrystal again with the increase of Sn content in the nanowires. Transmission electron microscopy result shows that the nanowires are about 50 nm in diameter and the aspect ratio is approximately 75. The magnetic response of the arrays was measured using vibrating sample magnetometry at room temperature. The results show that the coercivity and squareness with the magnetic field along the nanowire arrays decrease with the increase of the Sn content. Nanowires exhibit obviously uniaxial magnetic anisotropy, and the easy magnetizing axis is parallel to the nanowires owing to the large shape anisotropy.

Smooth single-crystal α-Mn 2 O 3 nanowires have been fabricated using a one-step solid-state reaction method. X-ray diffraction patterns show that the nanowires have pure phase of α-Mn 2 O 3 . Transmission electron microscopy was employed to investigate the size and morphology of the products. The α-Mn 2 O 3 nanowires exhibit mean diameter of 50 nm and length of 10 μm. Selected-area electron diffraction pattern demonstrates the single-crystal structure of the α-Mn 2 O 3 nanowires, which are in good agreement with the X-ray diffraction results. The processes of the reactions and the phase transitions were also studied by using a simultaneous thermal gravimetric/differential thermal analyzer. It is found that the concentration of the precursor MnCO 3 is a crucial factor in the formation of the nanowires. This work provides the probability of the industrialization of fabricating smooth single-crystal α-Mn 2 O 3 nanowires.

X-ray diffraction and Mossbauer spectroscopy are performed to investigate γ-Fe 1-x Ni x alloys and their nitrides γ'-(Fe 1-x Ni x ) 4 N with corresponding composition. X-ray diffraction shows that both alloys and nitrides have face-centered cubic crystal structure with approximately 18 to 20% expansion in volume of the nitrides. Mossbauer spectra at room temperature show drastic changes before and after nitrogenation. The changes are also rather different for the samples with lower nickel concentrations and those with the higher ones. For x = 0.25 and 0.30, the alloys mainly exhibit paramagnetic singlets while the nitrides exhibit complex ferromagnetic sextets. For x = 0.75 and 0.78, however, the alloys show ferromagnetic sextets while the nitrides show paramagnetic doublets. The reason for this is carefully discussed in terms of the lattice parameter dependence of Curie temperatures, which is caused by the introduction of interstitial nitrogen atoms into the Fe-Ni alloy structure.

Fe-rich Fe96-xZrxB4 (0≤x≤7) nanowires were first prepared by electrodepositing into anodic aluminum oxide templates. Transmission electron microscope analysis shows that the nanowires are uniform and are about 100 nm in diameter with an aspect ratio of around 75. The broad peaks of X-ray diffraction and the Mossbauer spectrum indicate that the Fe96-xZrxB4 nanowires are composed of α-Fe-like and Zr-rich FeZrB phases. Selected area electro diffraction results also indicate that the structure of Fe89Zr7B4 nanowires is amorphous. A vibrating sample magnetometer is employed to study the magnetic properties of nanowire arrays at room temperature. The coercivity of nanowire arrays in parallel to the wire axis decreases with increasing Zr content.

Mossbauer spectroscopy was used to investigate the influence of Nd-substitution on the hyperfine field distribution and isomer shift of amorphous FeB alloys. It is observed that a small addition of Nd causes the decrease of average hyperfine field and isomer shift and an increase of the width (ΔH) of the hyperfine field distribution P(H). At low temperature the average hyperfine field of amorphous Nd 4 Fe 77.5 B 18.5 alloy shows a temperature dependence of H a (T) = H a (0)(1 − BT 3/2 ) with a larger value of B than that of amorphous Fe 81.5 B 18.5 alloys.

Ultrafine (Fe0.7Co0.3)100−xBx amorphous powders with boron content x in the range of 27 to 40 at% are prepared by borohydride reduction without oxide of Fe3+ in the samples. With increasing boron content the average hyperfine field decreases and the average isomer shift increases. Comparing the hyperfine parameters of FeCoB powder with those of FeB powder having the same compositions, it can be seen that the average hyperfine fields and isomer shifts are quite different and the local environment of FeCoB powder is more complicated than that of FeB amorphous powder. DSC results indicated that the stability of the powder increases with increasing B content. Durch Borhydridreduktion werden ultrafeine, amorphe (Fe0.7Co0.3)100−xBx-Pulver mit einem Borgehalt von x im Bereich von 27 bis 40 At% hergestellt. In den Proben befindet sich kein Fe3+-Oxid. Mit wachsendem Borgehalt nimmt das mittlere Hyperfeinfeld ab und die mittlere Isomerverschiebung nimmt zu. Ein Vergleich der Hyperfeinparameter der FeCo;B-Pulver mit denen der FeB-Pulver mit gleicher Zusammensetzung ergibt, das die mittleren Hyperfeinfelder und Isomerverschiebungen vollig unterschiedlich sind und die lokale Umgebung der FeCoB-Pulver komplizierter ist als die der amorphen FeB-Pulver. DSC-Ergebnisse zeigen, das mit wachsendem B-Gehalt die Stabilitat der Pulver zunimmt.

Amorphous NdxFe81B19-x (0≤x≤19) alloys have been studied by57Fe Mossbauer spectroscopy. It is found that the average and peak hyperfine fields and the isomer shift decrease with increasing Nd content x. The magnetization for the samples containing Nd shows a strong tendency to lie in the direction perpendicular to the ribbon plane and its direction varies with Nd content.

Carbide of composition Gd2Fe17Cx compound with higher carbon concentration x = 2 was successfully prepared by the melt quenching. Fe-57 Mossbauer spectra of the carbides (x = 0, 1, 2) were measured at room temperature, the results show that the changing tendency of average hyperfine field and isomer shift is consistent with that of the carbides with x < 1.5. The effects of the interstitial carbon atoms in the Gd2Fe17 compound on the hyperfine parameters were discussed.

FeTa films with thickness of 110 nm are fabricated on glass substrates by magnetron sputtering, and then a series of strips is designed on the FeTa films by conventional optical lithography and the ion beam etching method. Patterned FeTa strips show a tunable in-plane uniaxial magnetic anisotropy property in contrast with the magnetic isotropic property of as-deposited FeTa thin films. The magnetization reversal mechanism of the patterned FeTa strips is investigated via the in-plane angular dependences of magnetization and coercivity. The angular dependence of coercivity (ADC) is explained well in terms of the two-phase model, giving good quantitative agreement with the experimentally measured M-shaped ADC curve. The domain structure and spatial resolution magneto-optical Kerr effect measurement indicate that the smaller the strip width, the stronger will be the anisotropy field. Regarding the dynamic magnetic properties, a transformation from Debye dispersion spectrum for strips with weak anisotropy to natural resonance spectrum for strips with strong anisotropy is finally obtained. The tunable in-plane anisotropy fields of the FeTa strips result in tunable high-frequency soft magnetic properties by altering the strip width, indicating that patterned FeTa strips have great potential in high-frequency soft magnetic application fields.

(Fe66.9Co33.1)86.8Sm13.2 (FeCoSm) thin films with thickness from 110 to 330 nm are fabricated on silicon (1 1 1) substrates by magnetron co-sputtering under ambient condition. The as-deposited FeCoSm thin film is amorphous when the thickness is less than 150 nm. When the thickness increases further, the film becomes partially crystallized. The maximum in-plane uniaxial anisotropy field is up to 1200 Oe. After the films are heat treated in vacuum with a magnetic field, the in-plane uniaxial anisotropy field decreases with an increase in annealing temperature and becomes zero after annealing at 500 °C. The dynamic magnetic properties of the FeCoSm films are also investigated in the range 0.1–9 GHz. Based on the one-terminal micro-strip transmission-line perturbation method and an analysis by the Landau–Lifshitz equation, the anisotropy field and the resonance frequency of the FeCoSm_films are in the range 50–1200 Oe and 1.8–12.1 GHz, respectively. The anisotropy field and resonance frequency of the film can be controlled by varying the film thickness or annealing temperature, this means that FeCoSm films have great potential in high-frequency applications.

FePt dot arrays with dot sizes ranging from 100 down to 15 nm were fabricated using sputtering, annealing and patterning techniques. The dot diameter distribution and dot position deviation are greater for smaller dot arrays than for larger dot arrays. The dot arrays produced through a sequence of annealing followed by patterning have a large perpendicular magnetic anisotropy resulting from the highly L10-ordered structure and the perpendicular orientation of the [0 0 1] crystalline axis, whereas samples of annealing after patterning display a magnetic vortex structure. As the dot size reduces from 100 to 29.9 nm, the arrays produced by annealing and then patterning exhibit an increase in the remanent coercivity H cr from 15.7 to 21 kOe because fewer defects are contained by the smaller dots. This result is explained by nucleation and domain wall propagation mechanisms. For 15.4 nm dot arrays, a model of dot with damaged edge may interpret the decreasing coercivity behaviour.