Structural and magnetic properties of FIB-irradiated microstructures on a Pt/Co multilayer

We present a study of the structural and magnetic effects induced by focused 30 keV Ga⁺ ion beam irradiation on a Pt(2.8 nm)/[Pt(0.6 nm)/Co(0.3 nm)]₆/Pt(6.5 nm) ferromagnetic multilayer, using transmission electron microscopy, optical and magneto-optical microscopy. The work is of relevance to high-density data-storage applications, where media planarity is crucial for device reliability.     

Magnetic properties of Co films and Co/Pt multilayers deposited on PDMS nanostructures

The magnetic properties of magnetron sputtered Co films (with in-plane anisotropy) and Co/Pt multilayers (with perpendicular anisotropy) deposited on elastomeric poly-dimethylsiloxane (PDMS) films and nanostructured templates are presented. Apart from the etched nanosize features, maze-like submicron features develop after the sputter deposition as a result of film buckling due to thermal contraction of the underlying PDMS layer. The nanostructured templates can physically isolate the magnetic entities but magnetic correlations within the range of the buckling features remain. By using oblique deposition geometries in-plane anisotropy develops and it is transferred to the PDMS buckling patterns. In the case of Co/Pt multilayers deposition on PDMS nanostructured templates results in a loss of the perpendicular anisotropy, attributed to the acuteness of the PDMS nanostructures.     

Magnetic properties of ultra-fine particles of Mn0.5Fe0.5Fe2O4 spinel system

A systematic study of the magnetic properties of ultra-fine particles of Mn_0.5Fe_0.5Fe₂O₄ spinel system has been undertaken. The effect of temperature on the magnetic properties of particles and the ferrofluid has been studied. Analysis of the data yields information on the anisotropy constant, particle size distribution and superparamagnetic behaviour. The results are explained on the basis of existing theories.     

High-frequency dynamics of Co/Fe multilayers with stripe domains

Within the framework of two-dimensional (2D) numerical micromagnetic simulations, the equilibrium magnetization configuration and the high-frequency (0.1–30 GHz) linear response of Co/Fe multilayers have been investigated in detail. Due to the perpendicular anisotropy of Co layers, a stripe domain pattern can develop through the whole multilayer, the characteristics of which depend on the magnitude of the perpendicular anisotropy, the respective thicknesses of Co and Fe layers and the number of Co/Fe bilayers in the stack. One of the most striking features associated with the layering effect is the ripening aspect of the static magnetization configuration across the multilayers which induces complicated dynamic susceptibility spectra including surface modes and volume modes strongly confined within the inner Fe layers. The effect of the cubic magnetocrystalline anisotropy of Fe layers and the influence of a nonuniform perpendicular magnetic anisotropy within the Co layers on the static and dynamic magnetic properties of Co/Fe multilayers are then analyzed quantitatively.     

Structure and magnetic properties of wedged Co/Ti multilayers

Co/Ti multilayers with wedge-shaped Co or Ti sublayers were prepared using UHV (5×10⁻¹⁰ mbar) DC/RF magnetron sputtering. The planar growth of the Co and Ti layers was confirmed in situ by X-ray photoelectron spectroscopy. Cobalt sublayers grow on sufficiently thick titanium sublayers in the soft magnetic nanocrystalline phase up to a critical thickness d_crit3.0 nm. For a thickness greater than d_crit, the Co sublayers undergo a structural transition to the polycrystalline phase with much higher coercivity. Furthermore, for the Co/Ti multilayers with nanocrystalline Co sublayers with d_Co=2.7 nm we have observed a significant drop of the coercivity — typically from H_c3.5 kA/m to H_c0.2 kA/m — for Ti thickness d_Ti0.35 nm. The above effect could be explained by the existence of a minimum Ti sublayer thickness (d_min0.35 nm), which is required for the nanocrystalline growth of Co, and/or the formation of quasi-continuous non-magnetic layers for d_Tid_min giving rise to a decrease of the exchange energy between Co sublayers. Magnetic domains and walls studies revealed the structural transitions of the Co sublayers.     

Magnetic force microscopic study of the magnetic field induced antiferro to ferrimagnetic transition in Mn1.85Co0.15Sb

Magnetic field induced first order antiferromagnetic (AFM) to ferrimagnetic (FRI) transition in polycrystalline Mn_1.85Co_0.15Sb has been studied using magnetic force microscopy (MFM) at 60 K and up to 8 T magnetic fields. Our MFM studies provide real space visualization of AFM to FRI transition. It shows growth (decay) of FRI phase with increasing (decreasing) magnetic field. The hysteretic behavior and co-existing FRI and AFM phases across the critical field required for FRI-AFM transition in Mn_1.85Co_0.15Sb are highlighted. This study demonstrates the potential of MFM for studying phase co-existence at high field and low temperatures.     

Magnetic properties and static-dynamic magnetostrictive characteristics for SmFe2/Fe exchange-coupled multilayers

Giant magnetostrictive SmFe₂/Fe exchange-coupled multilayers were fabricated by ion beam sputtering deposition on glass substrates. The effects of SmFe₂/Fe exchange coupling action and vacuum annealing on soft-magnetic property and static-dynamic magnetostrictive characteristics of SmFe₂/Fe multilayers were investigated. The results showed that the soft-magnetic, static-dynamic magnetostrictive characteristics were greatly improved by SmFe₂/Fe exchange coupling action and proper vacuum annealing treatment temperature. Compared with that of SmFe₂ single film, the coercivity in the direction of easy magnetization axis for SmFe₂/Fe exchange-coupled multilayers exhibited a greater decrease. Better soft-magnetic properties were achieved (H_c=2.54 kA/m, M_s=120.38 emu/g, and M_r/M_s=0.21) after vacuum annealing at certain temperature. The magnetostrictive coefficient for SmFe₂/Fe exchange-coupled multilayers was about 135 ppm at 16 kA/m magnetic field. At first order resonant frequency (99.2 Hz), the amplitude peak-peak value for the as-deposited SmFe₂/Fe exchange-coupled multilayers was 46 μm. After the vacuum annealing treatment at 250 °C, the amplitude peak-peak value increased to 650 μm.     

MFM studies of magnetic domain patterns in bulk barium ferrite (BaFe12O19) single crystals

Magnetic domain patterns in bulk barium ferrite (BaFe₁₂O₁₉; BaM) single crystals on the basal plane and the prism plane were measured and studied by magnetic force microscopy (MFM). The surface domain pattern is in the form of flowers or star on the basal plane and long elongated spikes or stripe domains on the prism plane. The change in domain structure with applied field (H_app) and the thickness (T) dependence on domain width (δ) was observed. The domain width decreased from 32 to 9 μm for the crystals of 800-100 μm thicknesses, respectively.     

Origin of perpendicular magnetic anisotropy and evolution of magnetic domain structure of amorphous Pr-TM-B (TM=Fe, Co) films

In this study, the deposition pressure dependence of the compositional ratio, magnetic domain structure, and perpendicular magnetic anisotropy (PMA) of B-containing PrFe- and PrCo-based films, which are rare-earth-transition-metal (RE-TM) films, was investigated. PrFe- and PrCo-based films were fabricated by magnetron sputtering. The film compositions were controlled in a wide range by varying the deposition pressure. On the basis of experimental results, the residual stress of the films was considered to be the possible origin of their PMA. The films showed strong magneto-optical effects over the entire wavelength range of 300-750 nm. Because of the excellent magnetic and magneto-optical (MO) properties of the films, they have high potential for MO applications at wavelengths of red and blue lasers.     

Temperature dependence of magnetic properties in Fe/Fe-O nanoparticles dispersed in water

Commercial water dispersions of Fe/Fe-O nanoparticles (∼50-80 nm diameter) were prepared bare and treated with a biodegradable polymer to stabilize the suspension. Hysteresis loops and FC-ZFC curves of samples in liquid and dried form were measured by means of a vibrating sample magnetometer from 77 to 300 K. A marked dependence on the conditioning field is observed in all samples that display the Verwey transition at about 120 K. The role of magnetic interactions on dried samples was also investigated by means of magnetoresistance measurements as a function of temperature.     

Surface vs. bulk magnetic properties of Co/Fe(0 0 1) and Fe/Co/Fe(0 0 1) as probed by linear magnetic dichroism in photoemission

The atomic-like behavior of the photoionization cross-section of core levels in solids is remarkably displayed in the observation of linear magnetic dichroism in the angular distribution (LMDAD) of photoelectrons. Nevertheless, structure-related effects are clearly visible as modulations of the dichroism signal, induced by photoelectron diffraction (PED). In this paper a comparison between the PED and LMDAD behaviours is presented for Fe 3p in Fe(0 0 1). In order to separate experimentally the surface and bulk contributions, ultrathin Co/Fe pseudomorphic overlayers were grown on the Fe(0 0 1) surface. Results confirms the PED nature of LMDAD modulations, which can be used as an estimate of the bulk sensitivity of the experiment.     

直流磁控溅射Si和玻璃衬底Fe/Co多层膜的磁性能比较

对直流磁控溅射Si和玻璃衬底［Co_t/Fe_3t］₅(t=2, 3, 4, 5nm)多层膜的磁性能进行了比较.对于t相同但衬底不同的样品，实验发现饱和磁化强度相差很小，但是矫顽力却相差很大.对矫顽力差异的理论分析表明，多层膜的粗糙度和畴壁类型是引起这种差异的主要原因.     

Magnetic field dependence optical properties of GaN/AlN multiple quantum wells

In this work, we have investigated the optical properties of some multiple quantum wells under the influence of an external magnetic field and (for the first time) number of wells. We have retained the total length of the structure constant which is technologically important. Then we have detected a blue shift in the absorption peak positions due to the application of the magnetic field and a red shift due to the increasing of the number of wells. The red shift is only seen in the multiple quantum wells with odd number of wells and the absorption peaks of the multiple quantum well with even number of wells are not changed.     

Magnetic properties of Mn3Si from first-principles studies

The Heusler compound Mn₃Si, the antiferromagnet in the Mn-based class of Heuslers which contains several conventional and half-metallic ferromagnet, shows a peculiar stability of its magnetic order in high magnetic fields. We investigated the electronic and magnetic properties of Mn₃Si by band structure calculations based on the density functional theory. The minority bands of Mn₃Si in the spin polarized state are gapped at the Fermi level, which shows a half-metallic behavior of Mn₃Si.     

Thin films of molecular materials synthesized from C32H20N10M (M = Co, Pb, Fe): Film formation, electrical and optical properties

In this work, the synthesis of molecular materials formed from metallic phthalocyanines and 1,4-phenylenediamine is reported. The powder and thin film (∼80-115 nm thickness) samples of the synthesized materials, deposited by vacuum thermal evaporation, show the same intra-molecular bonds in the IR spectroscopy studies, which suggests that the thermal evaporation process does not alter these bonds. The morphology of the deposited films was studied using scanning electron microscopy (SEM) and atomic force microscopy (AFM) and their optical and electrical properties were studied as well. The optical parameters have been investigated using spectrophotometric measurements of transmittance in the wavelength range 200-1200 nm. The absorption spectra recorded in the UV-vis region for the deposited samples showed two bands, namely the Q and Soret bands. The optical activation energy was calculated and found to be 3.41 eV for the material with cobalt, 3.34 eV for the material including lead and 3.5 eV for the material with iron. The effect of temperature on conductivity was measured for the thin films and the corresponding conduction processes are discussed in this work.