添加AlN对FePt薄膜结构和磁性的影响

采用射频磁控溅射制备了FePt(50nm)和[FePt(2,3,5nm)/AlN(1nm)]n膜,之后在550℃退火30min,研究了周期数(n)和AlN含量对[FePt/AlN]_n系列多层膜结构及磁性的影响.结果表明,多层膜的矫顽力和矩形比均在n=8时出现较大值;周期数的增大会引起晶粒尺寸的长大;AlN的加入不但可以抑制FePt粒子的长大,使晶粒体积(V_grain)和磁激活体积(V*)趋于一致,而且还能有效地降低晶粒间交换耦合作用,并且AlN含量越大,晶粒间交换耦合作用的程度越弱.     

Effect of annealing in external magnetic field on the microstructure and magnetic properties of FePt films

We have studied the influence of annealing in an external magnetic field on the microstructure and magnetic properties of a multilayer Si/Fe(2 nm)/Fe₅₀Pt₅₀(20 nm)/Pt(2 nm) structure synthesized by means of sequential RF magnetron sputtering of the components. The magnetic field was oriented perpendicular to layers of the structure. It is established that annealing in the external magnetic field leads to the formation of predominant (001) texture in the multilayer structure with L1₀-FePt phase. Thus, a method of obtaining multilayer structures based on FePt films required for the perpendicular magnetic recording has been developed.     

Grain Refining and Decoupling in FePt/SiO2 Nanogranular Films for Magnetic Recording

FePt/SiO₂ nanogranular thin films have been prepared by molecular-beam epitaxy system on MgO (001) substrates with the method of insertion dual SiO₂ layers into Fe/Pt multilayer films. We report the relationships between the inserting thickness of SiO₂ layers and the microstructural and magnetic properties of FePt thin films. It indicated the nanogranular FePt thin films were successfully formed by inserting amorphous SiO₂ layers into the Fe/Pt films. The reduction of grain/domain size and isolation of FePt particles can be achieved by such insertion and maintain (001) texture. The average grain size of FePt films with 5-nm SiO₂ insert layers is estimated to be around 8 nm, while domain rotation is enhanced depicting a decoupling of intergrain interaction. The isolated grains are less magnetically coupled in the rotation mode and the reversal of magnetization is more independent     

Effect of AlN layer thickness on structure and magnetic properties of FePt/AlN multilayers

FePt (50 nm) and [FePt(xnm)/AlN(1, 2, 3 nm)]₁₀ (x=2, 3 nm) films were prepared by RF magnetron sputtering technique, then were annealed at 550 °C for 30 min. This work investigates the effect of AlN layer thickness on structure and magnetic properties of FePt/AlN multilayers. Superlattice (0 0 1) peaks can be found in the grazing incidence X-ray diffraction of FePt and [FePt (3 nm)/AlN (1, 2, 3 nm)]₁₀ films, which indicate that the FCC phase has been partially transformed into ordered L1₀ phase. Compared with the single layer FePt film, superlattice (0 0 1) peaks of FePt/AlN multilayers are weak and wide, which indicates that the introducing of AlN hinders the growth of FePt particle, and also shows the introducing of AlN is not beneficial to the transformation from FCC phase to L1₀ phase. In addition, the low-angle XRD spectra show the layered structure of FePt/AlN has been broken after annealing. The coercivities, particle size, intergrain exchange interactions of FePt/AlN films are decreased with increasing AlN layer thickness.     

Structure and magnetic properties of sputtered FePtM (M = Ti,Nb) thin films

FePt thin films doped with various Ti and Nb concentrations ranging from 2.9 to 9.1 at.% were prepared by r.f. magnetron sputtering. The structural and magnetic properties of Ti- and Nb-doped FePt thin films were investigated. Structural studies revealed that the long range ordering in FePt thin films depends on the doping concentration and annealing temperature of FePt thin films. The addition of Ti and Nb is found to enhance the grain refining in FePt thin films. The effects of doping concentration on the magnetic properties of FePt thin films were studied and discussed.     

High-density perpendicular magnetic recording media of granular-type (FePt/MgO)/soft underlayer

Perpendicular magnetic recording media, composed of granular-type FePt-MgO films on Fe-Ta-C soft magnetic underlayer (SUL), have been fabricated on to 2.5-in glass disks. [001] textured FePt granular films with high-perpendicular magnetic anisotropy were obtained by annealing the FePt/MgO multilayer films. The FePt grain size, perpendicular coercivity, magnetic activation volume, and the exchange coupling between the FePt grains were found to be strongly dependent on the initial multilayer structures and the annealing conditions. The recording performance of the disks was evaluated by a spin-stand. The obtained results reveal a close correlation between the recording performance and magnetic properties. The thermal stability of the granular-type FePt media was studied using high-temperature magnetic force microscopy (MFM) technique, equipped with in situ sample heating, in the temperature range 25/spl deg/C-200/spl deg/C. The estimated signal decay at high temperature is ascribed to the temperature dependent magnetic anisotropy behavior.     

Oscillatory behavior of the magnetic properties of Nd–Fe–B films with Mo and Mo–Cu additions

A series of Ta/NdFeB/Ta thin films with Mo and Mo–Cu additions embedded by alloying and by stratification have been prepared by r.f. sputtering. The influence of additions, their embedding mode, and annealing temperature on the structural and magnetic behavior of Ta/NdFeB/Ta thin films is presented. The use of additions of Mo and Mo–Cu leads to refined grain structure and improvement in the hard magnetic characteristics of Ta/NdFeB/Ta thin films. The Ta/[NdFeBMo(540 nm)/Ta films and Ta/[NdFeB(180 nm)/MoCu(dnm)] × n/Ta multilayer films present enhanced coercivities and M_r/M_s ratios in comparison with the Ta/NdFeB(540 nm)/Ta films. The stratification of Ta/NdFeB/Ta thin films with Mo–Cu interlayers leads to an oscillatory behavior of hard magnetic characteristics of the Ta/[NdFeB(180 nm)/MoCu(dnm)] × n/Ta multilayer films, when the thickness, d, of Mo–Cu interlayers varies by increments of 1 nm. When the thickness of Mo–Cu interlayers varies by increments of 2 nm the oscillatory behavior of the magnetic characteristics is not revealed. For a thickness of the Mo–Cu interlayer of 3 nm in the Ta/[NdFeB(180 nm)/MoCu(3 nm)] × 3/Ta thin films annealed at 650 °C, the c-axis of part of the hard magnetic Nd₂Fe₁₄B grains is oriented out-of-plane.     

Preparation and magnetic properties of electrodeposited [Co/Zn] multilayer films

In this report we describe some experimental results concerning the preparation by electrodeposition and characterization of Co/Zn multilayer films, a system of special significance because Co and Zn are immiscible in a large range of compositions, permitting an easier adaptation of the sharp interfaces and the magnetic interactions between layers, with a view to obtain technological applications in nano-electronics. We established the working parameters for electrodeposition of multilayer films based on Co and Zn nanoscale layers, using a dual-bath potentiostatic electrodeposition method. The effect of the first electrodeposited layer growth process on the structure and magnetic properties of the multilayer were studied by using two series of multilayers of varying periods, starting with Co or Zn layers, respectively (with the same total thickness of Co layers, namely 50 layers of 5 nm thick, but various Zn layer thickness). These properties were also studied as a function of the Zn layer thicknesses (varying between 0.1 nm and 5.9 nm), for the two series of films. The magnetoresistance (in the current in plane configuration with dc magnetic field applied in the film plane), varied with Zn layer thickness, exhibiting a giant magnetoresistance contribution of about 30% in the case of [Co (5 nm)/Zn (2.7 nm)]₅₀ films.     

Magnetic properties of permalloy/permalloy-oxide multilayer thin films

Magnetic properties of permalloy/permalloy-oxide multilayer thin films are investigated. These thin films are prepared by a repeat of sputter deposition of permalloy thin film, followed by oxidation of the film surface. The total thickness of the permalloy thin films before oxidation is about 100 nm. The number of layers is one to twenty. The oxide layers are formed by oxidation in dry air. The estimated oxide layer thickness is about 2 nm. The oxide NiFe₂O₄ is identified by RHEED. The film coercivity decreases linearly with increasing layer numbers. The saturation magnetization and magnetoresistivity decrease as the number of layers increase. The coercivity decrease is due to grain growth suppression and magnetic separation by oxide film of permalloy layer, and magnetoresistivity decrease is due to electrical resistivity increase originating into electron scattering by the oxide layer.     

Low temperature ordering of FePt films by in-situ heating deposition plus post deposition annealing

FePt thin films with 40 nm thickness were prepared on thermally oxidized Si (001) substrates by dc magnetron sputtering at the nominal growth temperature 375 °C. The effects of annealing on microstructure and magnetic properties of FePt thin films were investigated. The as-deposited FePt thin films show soft magnetic properties. After the as-deposited FePt thin films were annealed at various temperatures and furnace cooled, it is found that the ordering temperature of L1₀ FePt phase could be reduced to 350 °C. For FePt thin films annealed at 350 °C, the in-plane and out-of-plane coercivities of the films increased to 510 and 543 kA/m, respectively, and the films had hard magnetic properties. A highly (001) orientation was obtained, when FePt thin films were annealed at 600 °C. And the hysteresis loops of FePt thin films annealed at 600 °C show out-of-plane magnetic anisotropy.     

The effect of thickness on the texture and magnetic properties of single-layered FePt films by rapid thermal annealing

The single-layered FePt films with thickness in the range of 5 to 50 nm are deposited directly on Si(100) substrate without underlayer, then post annealed at 700 degrees C by rapid thermal annealing (RTA) technique. As the film thickness of FePt is over 20 nm, the L1(0) FePt(111) preferred orientation is presented and tended to in-plane magnetic anisotropy. However, the L1(0) FePt(001) texture is obtained and exhibited perpendicular magnetic anisotropy as the film thickness is decreased to 10 nm. Its perpendicular coercivity (Hc(perpendicular)), saturation magnetization (Ms) and perpendicular squareness (S(perpendicular)) are 14.8 kOe, 795 emu/cm3 and 0.79, respectively. On the other hand, both the grain size and domain size of FePt film decrease with decreasing the film thickness of FePt. The grain size for 10-nm FePt film is as small as 9.7 nm with domain size of 123 nm, which reveal its significant potential as perpendicular magnetic recording media for ultra high-density recording.     

Effects of Magnetic Annealing on Structure and Magnetic Properties of L10-FePt/Ag Films

The structural and magnetic properties of L1₀-FePt/Ag films were studied by X-ray diffraction and a vibrating sample magnetometer. The FeAg/Pt films were obtained by depositing FeAg thin films on thermally oxidized Si (001) substrates via magnetron sputtering and Pt layers on their surface after annealing FeAg thin films at 400 °C with and without an out-of-plane magnetic field of 10 kOe. These films were further annealed at various temperatures to obtain L1₀-FePt phase. The results indicated that the pre-annealing of FeAg thin films under 10 kOe magnetic field caused (001) orientation of Fe particles, and the deposition of Pt layer on such orientated underlayers reduced the ordering temperature of FePt in FeAg/Pt films, realizing the L1₀-FePt phase at 400 °C. The higher coercivity and ordering degree were also observed in the samples, compared with those pre-annealed without magnetic field at the same annealing condition.     

Annealing effect on the structure and electronic transport properties in La5/8Ca3/8MnO3/ErMnO3 multilayer thin films

Ferromagnetic La5/8Ca3/8MnO3 (LCMO) and Ferroelectric ErMnO3 (EMO) multilayer thin films with sandwich structure (LCMO/EMO/LCMO) were grown on (LaAlO3)0.3(Sr2AlTaO6)0.7 (001) [LSAT (001)] substrates by pulsed laser deposition (PLD) method. For these films, the structural characterization was carried out by X-ray diffraction (XRD), and the temperature-dependence resistivity (p-T) showing the metal-insulator transition (Tp) also was measured. In the multilayer thin films the LCMO (002) peak move to lower Bragg angles after annealing at 900 degrees C for 30 hours under 1atm Oxygen pressure, and this condition is much different from the LCMO single layer films where the (002) peak moves to higher Bragg angle after annealing due to the lattice mismatch between the LCMO layer and the substrate. By increasing the thickness of LCMO, the multilayer samples show two MR peaks in a wide temperature range during the process of M-l transition. This phenomenon is attributed to a new (La5/8Ca3/8)xEr(1-x)MnO3 layer produced by the solubility between LCMO and EMO layers after high-temperature annealing. In this paper, we provide some evidence of dissolution between LCMO and EMO layers, and discuss the influence on structure and electronic transport properties in the composite thin films by annealing.     

Sintering Effect of Annealed FePt Nanocrystal Films Observed by Magnetic Force Microscopy

Chemically synthesized FePt nanocrystals can exhibit room temperature ferromagnetism after being annealed at temperatures above 500degC. In thick films composed of FePt nanocrystals, the coercivity can be quite large. However, the coercivity of thin films has been found to decrease significantly with decreasing thickness, to the point that ferromagnetism at room temperature is lost. We studied 12 to 55 nm thick films by using magnetic force microscopy (MFM) under external applied fields. We made smooth films by spin casting 4-nm-diameter FePt nanocrystals and annealing them at 605degC-630degC. Thin FePt films showed lower coercivity than thick films. To help interpret the MFM images, we obtained complementary magnetic and structural data by superconducting quantum interference device (SQUID) magnetometry, transmission electron microscopy (TEM), and X-ray diffraction. We conclude that the magnetic properties of these films are strongly affected by nanocrystal aggregation that occurs during annealing     

Optimization of L10-FePt/MgO/CrRu thin films for next-generation magnetic recording media

L1₀-FePt thin films were deposited on silicon substrates with the structure of Si/CrRu/MgO/FePt. The magnetic and microstructural properties were optimized by varying the FePt sputter pressure and temperature, as well as the thicknesses of all three layers. High coercivity films greater than 1.8 T were grown when the FePt sputter pressure was at 1.33 Pa with a thickness of only 4 nm, on CrRu and MgO underlayers as thin as 10 nm and 2 nm, respectively.     

Microstructure and magnetic properties of (0 0 1)-oriented L10 FePt films: Role of Ag underlayer and Fe/Pt ratio

FePt multilayer films were deposited on Si(1 0 0) substrate with thermally grown SiO₂ film and sputtered Ag underlayer at room temperature by dc magnetron sputtering and subsequently annealing in vacuum. Experimental results suggest that proper thickness of Ag underlayer and slightly rich of Fe content can effectively induce the (0 0 1) texture of FePt films. A Fe_57.4Pt_42.6 thin film on the 8 nm Ag underlayer exhibits a large perpendicular coercivity of 7.6 kOe with magnetic remanence close to 1.     

Microstructure and magnetic properties of Ti/CoCrPt/Ti pseudo-sandwich nanogranular films

We prepared Ti/CoCrPt/Ti pseudo-sandwich granular films by radio-frequency and dc magnetron sputtering onto glass substrates and subsequent in situ annealing. We investigated the microstructure and magnetic properties of the films as a function of Ti overlayer thickness (x). X-ray diffraction profiles show that the CoCrPt magnetic layers are formed as the hexagonal close-packed (HCP) structure. Vibrating sample magnetometer measurements indicate that the out-of-plane coercivity reaches the maximum 1675.5 Oe when x=5 nm. Atomic force microscopy images show the minimum average grain size D=7.2 nm and the average roughness R/sub a/=1.0 nm. Magnetic force microscopy images show that the minimum average magnetic cluster size is about 6.4 nm at x=5 nm.     

Structure and magnetic properties of nanostructured Pd-Fe thin films produced by pulse electrodeposition

Nanostructured Pd-Fe thin films with varied Fe content were prepared by electrodeposition technique from organic electrolytes on Cu and brass substrates. The structure and the magnetic properties of the films were investigated prior to post-deposition annealing. The structure of the Pd1-xFe(x) thin film with x = 0.14, 0.24, and 0.52 was determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM) as a solid solution of iron in palladium face-centered cubic lattice with the (111) orientation of nanograins relatively to the substrate surface. The films with higher iron concentration, x = 0.74, 0.91, have structure of a solid solution based on the body-centered cubic lattice. The average grain size determined by the scanning electron microscopy (SEM) for the first two alloys is 7-10 nm, and for the latter ones it is about 120 nm. The saturation magnetization of the films has linear dependence on the iron content, but coercivity has non-monotonic dependence on x, i.e., the films with x = 0.68 show highest coercivity. The magnetic anisotropy of the samples is studied by ferromagnetic resonance (FMR) spectroscopy.     

Effect of capped layer on microstructure and magnetic properties of FePt films

Sputter-deposited FePt films exhibit an in-plane magnetic anisotropy when MgO is used as the capped layer. The perpendicular magnetic anisotropy of FePt films can be enhanced by introducing a Ag capped layer instead of a MgO capped layer. Although the in-plane coercivity (Hc_//) of FePt films decreases slightly after introducing a Ag capped layer instead of a MgO capped layer, the perpendicular coercivity (Hc_⊥) is increased significantly from 3169 Oe to 6726 Oe. Auger electron spectroscopy analysis confirms that Ag atoms diffuse from the capped layer into the FePt magnetic layer and are mainly distributed at the grain boundary of FePt. This phenomenon results in enhancement of the grain boundary energy and inhibition of grain growth, thus increasing the perpendicular coercivity and reducing the grain size of the FePt film.     

Lattice Expansion by Adding Oxygen to Control Crystallographic Orientations in Chemically Ordered L10 FePt Films

We fabricated L1₀ FePt thin films by sputtering in reactive oxygen on polycrystalline glass substrates, and we investigated the magnetic properties and crystallographic orientations of the films. Oxygen addition during the FePt deposition promoted heteoroepitaxial growth by decreasing the lattice misfit with the Ag underlayer. In an oxygen/argon ratio of 1.5-3.0 vol.%, the in-plane lattice parameter of the FePt films expanded, and the lattice misfit with the Ag underlayer decreased from 6.3 to 3.9% in the as-deposited state, as determined by grazing incidence X-ray diffraction (GIXRD). Annealing at 700degC for 1 min produced a heteroepitaxially grown L1₀ (001) texture with a large out-of-plane coercivity of 8.8 kOe and a nucleation field of kOe. Transmission electron microscopy showed that average grain size in the as-deposited films was about 4-5 nm and was in the range of 10-15 nm in the annealed films, indicating that there was some grain growth.