Magnetic Properties Of FePt Research Articles

Influence of Cu on the Improvement of Magnetic Properties and Structure of L10 FePt Nanoparticles.

L10 ordered FePt and FePtCu nanoparticles (NPs) with a good dispersion were successfully fabricated by a simple, green, one-step solid-phase reduction method. Fe (acac)3, Pt (acac)2, and CuO as the precursors were dispersed in NaCl and annealed at different temperatures with an H2-containing atmosphere. As the annealing temperature increased, the chemical order parameter (S), average particle size (D), coercivity (Hc), and saturation magnetization (Ms) of FePt and FePtCu NPs increased and the size distribution range of the particles became wider. The ordered degree, D, Hc, and Ms of FePt NPs were greatly improved by adding 5% Cu. The highest S, D, Hc, and Ms were obtained when FePtCu NPs annealed at 750 °C, which were 0.91, 4.87 nm, 12,200 Oe, and 23.38 emu/g, respectively. The structure and magnetic properties of FePt and FePtCu NPs at different annealing temperatures were investigated and the formation mechanism of FePt and FePtCu NPs were discussed in detail.

Temperature Dependence and Microstructure Effects on Magnetic Properties of FePt(B, Ag, C) Film.

A FePt(B, Ag, C) granular film was formed from post-annealed B4C(1.0 nm)/FePt(Ag, C) layers at a substrate temperature of 470 °C for 2 min. The 6 nm thick FePt(B, Ag, C) film demonstrates high perpendicular magnetic anisotropy (Ku = 2.83 × 107 erg/cm3 at 100 K) and out-of-plane coercivity (Hc = 38.0 kOe at 100 K). The Ku and out-of-plane Hc are respectively increased from 38% and 46% between 350 K and 50 K. The sample with a thickness of 8 nm also shows a similar trend for magnetic properties; however, the tiny magnetization kink which may come from rare Fe-B or disordered FePt grains was observed in the easy axis loop. The intrinsic (ΔHint = 12.6 kOe) and extrinsic switching field distribution (ΔHext = 1.62 kOe) were characterized by major and minor loops to correlate the microstructural grains. The coupled FePt grains grown on a single MgTiON grain were observed in a high-resolution transmission electron microstructure (HRTEM) image. This small intergranular exchange coupling was defined by estimating the magnetic cluster size (46.6 nm) from ΔHext and the average grains size (28.2 nm) from TEM images. The temperature dependence of coercivity was fitted to further understand the magnetization reversal process. The lower microstructural parameter was evidenced in the imperfect grain morphology.

Microstructure and magnetic properties of nanocrystalline Fe-Pt-based ribbons

The structural and magnetic properties of FePt – magnetic nanocomposites prepared by isothermal annealing of melt-spun Fe52Pt28Nb2B18 and Fe51Pt27Nb2B20 ribbons are reported. As it was evidenced the as-cast samples consists of L10-FePt hard magnetic grains dispersed in a predominant soft magnetic matrix composed of A1 FePt, Fe2B and boron-rich (FeB)PtNb residual phases. The applied annealing procedure reflects in temperature-induced structural and magnetic transition of dominated A1 FePt phase into L10-FePt dependent on Fe-Pt composition. As it was shown the Fe52Pt28Nb2B18 ribbon annealed at 700 °C exhibit promising hard magnetic properties at room temperature manifested as reasonably high remanence to saturation ratio (Mr/Ms = 0.68); coercivity (Hc = 0.92 T) and (BH)max = 83 kJ/m3 parameter. Strong exchange coupling between both FePt – based hard and soft magnetic phases was demonstrated by a smooth demagnetizing curve.

Magnetic Properties and Microstructure of FePt(BN, Ag, C) Films

The microstructure and magnetic properties of FePt(BN, Ag, C) granular films grown on the MgTiON intermediate layer with and without the MoC inserting layer were studied. Without the MoC inserting layer, the 6 nm thick FePt film is continuous, which favors the domain wall motion magnetization reversal process and shows a lower out-of-plane coercivity (Hc) value of 6.7 kOe. The FePt(BN, Ag, C) granular film was grown in ball- and square-like grains with an almost vertical contact angle, and the out-of-plane coercivity (Hc) was increased to 15.5 kOe. When the MoC with a thickness of 3 nm was capped on the MgTiON intermediate layer, the FePt grains with and without (BN, Ag, C) segregants were both formed in large trapezoidal islands with a low contact angle morphology. The out-of-plane Hc value changed from 14.9 to 13.2 kOe and the reduced coercivity was due to larger grain sizes and a lower ordering degree of the FePt(BN, Ag, C) film.

Microstructure and magnetic properties of FePt-(C,SiO2) granular films deposited on MgO, MgTiO, and MgTiON underlayers

We investigated the microstructure and magnetic properties of FePt-(C,SiO2) granular films deposited on MgO, MgTiO, and MgTiON underlayers. The coercivity and grain size of the FePt-(C,SiO2) film are substantially degraded when deposited on the MgTiO underlayer compared to those on the MgO underlayer, while they become comparable when deposited on the MgTiON underlayer. Atomic resolution STEM-EDS showed Ti in the MgTiO underlayer diffuses into FePt grains, while it is suppressed using the MgTiON underlayer. This suggests that MgTiON is a good choice for a conductive underlayer for growing L10-FePt perpendicular recording media for heat assisted magnetic recording.

Effects of B4C Addition on the Microstructure and Magnetic Properties of FePt-C Granular Thin Films for Perpendicular Magnetic Recording

Effects of B4C addition on the microstructure and magnetic properties of FePt and FePt-C thin films have been studied. A high coercivity of 2.11 T with good squareness is achieved by B4C addition. By analyzing the mechanism and different isolation effects of B4C and C as segregants, a double-layer approach has been developed and a coercivity of 1.96 T is achieved with column-like FePt grains. The grain size and the size distribution are not deteriorated substantially compared with the single-layer case. These results indicate that addition of B4C as segregant is beneficial for the modification of microstructure and magnetic properties.

Investigation of microstructure and magnetic properties of FePt–X films grown on MgO and STO substrates

Different thickness (001) textured FePt–X films were fabricated on MgO and SrTiO3 substrates, and the microstructure and magnetic properties of FePt–X films was systematically investigated. The study showed that the substrates with different lattice mismatch resulted in different crystallographic texture and microstructure. The larger mismatch strain with using MgO substrates would cause FePt films to follow the island growth mode, and the negligible mismatch strain with using STO substrate would form continuous film. Doping SiNx and C into FePt films caused the increase of lattice mismatch strain between FePt and MgO/STO, which would induce FePt films to forming island growth. The perpendicular anisotropy of FePt–SiNx–C films grown on MgO substrate was larger than that of using SrTiO3 substrate, which was attributed to the larger strain induced by larger lattice mismatch.

Granular nanostructures and magnetic properties of FePt–C/FePt–SiO2 films

FePt–C, FePt–SiO2 and FePt–C/FePt–SiO2 films with different segregants concentration on glass substrate with polycrystalline MgO underlayer have been successfully fabricated by magnetron sputtering system. It was found that the FePt–C films had larger coercivity(Hc), chemical order parameter(S) and smaller diameter of the local interaction zone(Dn) but wider magnetic coercive force distribution(ΔHc/Hc) than that of the FePt–SiO2 films. By using FePt–C/FePt–SiO2 bilayer structure, the low Dn and ΔHc/Hc were obtained. FePt–C30vol%(4 nm)/FePt–SiO245vol%(4 nm) film with Hc higher than 29 kOe and columnar FePt grains of 10 nm in diameter and 13 nm in height were obtained, which would be very suitable for heat assisted magnetic recording media.

Effect of MgO underlayer misorientation on the texture and magnetic property of FePt–C granular film

A transmission electron microscope (TEM) based orientation mapping technique and micromagnetic simulations were applied to study the influence of easy axis distribution (EAD) on magnetic properties of FePt–C granular films which were deposited on a single crystalline MgO (001) substrate and a (001)-textured poly-crystalline MgO underlayer. The FePt–C film on the polycrystalline MgO underlayer shows smaller perpendicular coercivity, broader switching field distribution and visible in-plane minor loop compared with that deposited on the single crystalline MgO (001) substrate. Although the grain sizes and their distributions in both films look similar in TEM, orientation mapping and texture analysis revealed that the polycrystalline MgO underlayer introduces significant misorientation in the (001)-textured FePt grains. Micromagnetic simulations successfully reproduced the large hysteresis in the in-plane magnetization by introducing the specific misorientation distribution of the FePt grains obtained from the texture analysis. The misoriented FePt grains were found to be grown from misoriented MgO grains, indicating that the improvement of the (001) texture of the MgO underlayer is essential to reduce the in-plane component of FePt based recording media.

Microstructure and Magnetic Properties of FePt–Cr2O3 Films

We have studied the microstructures and magnetic properties of FePt with various metal oxides, to achieve an ideal media structure on glass substrates for thermally assisted magnetic recording. Unlike FePt-C granular films, FePt-MxOy(M = Ti, Nb, W, Zr, and Al) granular films showed an interconnected in-plane microstructure and low coercivity. However, the usage of Cr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> as a segregant leads to very fine columnar granular structure, while there is still room for improvement in coercivity.

Effect of nitrogen upon structural and magnetic properties of FePt in FePt/AlN multilayer structures

This paper investigates the effect of the addition of nitrogen in FePt layers for ultrathin FePt/AlN multilayer structures. X-ray diffraction results reveal that a compressive stress relaxation occurs after annealing owing to the release of interstitial nitrogen atoms in the FePt layers. The introduction of nitrogen also induces a large in-plane compressive strain during grain growth not seen in FePt deposited without nitrogen. This strain is considered to decrease the driving force for (111) grain growth and FePt ordering.

Microstructures and Magnetic Properties of FePt Thin Films on TiON Intermediate Layer

The microstructures and magnetic properties of FePt(-SiOx-C) thin films grown on TiON and TiON/TiN intermediate layers were studied. TiON possessed smaller surface energy and smaller lattice constant than TiN. With increasing TiOx doping concentration, FePt grain shape changed from semi-spherical to square and grain size was significantly reduced. Meanwhile, good perpendicular magnetic anisotropy was retained, indicating that TiON intermediate layer could achieve a good balance between island growth and epitaxial growth. Furthermore, using TiON/TiN combined intermediate layer, FePt grain size was further reduced and the opening-up of in-plane M-H loop diminished. With 45 vol.% SiOx-25 vol.% C doping, well-isolated FePt grains with an average size as small as 5.7 nm and the grain size distribution of 0.9 nm were achieved. It also exhibited good perpendicular magnetic anisotropy with an out-of-plane coercivity of 18 kOe.

Microstructure and magnetic properties of FePt(B4C) and FePt(B4C–Ag) granular films with perpendicular magnetization

Abstract Multilayers [FePt/B 4 C ( t nm)] 10 ( t = 0–0.4) and [FePt/(B 4 C) y Ag 1− y (0.1 nm)] 10 ( y = 0.2–0.8) films were deposited on a glass substrate and subsequently annealed by a rapid thermal process (RTP) at 800 °C for 3 min. After RTP, the granular FePt(B 4 C) and FePt(B 4 C–Ag) films with perpendicular magnetization were formed. The FePt grains were interconnected in FePt(B 4 C) films and further broken into the small round grains in FePt(B 4 C–Ag) films. In FePt(B 4 C) films, the maze-like structure with worm shape FePt grains but the grains boundaries were still defined. The granular structure with well defined boundaries was formed when the minor Ag was added to partial replace B 4 C. The immiscible (B 4 C, Ag) were demonstrated as segregant to separate FePt grains without affecting c -axis alignment. The FePt grains were separated uniformly with size distribution 19% and the average grains size was 13.5 nm in (Fe 0.48 Pt 0.52 ) 90 [(B 4 C) 0.6 Ag 0.4 )] 10 film. The average grains size of FePt was 10. 6 nm in (Fe 0.48 Pt 0.52 ) 90 [(B 4 C) 0.2 Ag 0.8 )] 10 film. The grains were more distanced and show magnetostatic coupling.

Fine Tuning Magnetic Properties of FePt:C Thin Films by FePt UnderLayers

Nonepitaxially grown FePt (x)/FePt:C thin films were synthesized, where FePt (x) (x=2, 5, 8, 11, 14 nm) layers were served as underlayers and FePt:C layer was nanocomposite with thickness of 5 nm. The effect of FePt underlayer on the ordering, orientation and magnetic properties of FePt:C thin films has been investigated by adjusting FePt underlayer thicknesses from 2 nm to 14 nm. X-ray diffraction (XRD), together with transmission electron microscopy (TEM) confirmed that the desired L10 phase was formed and films were (001) textured with FePt underlayer thickness decreased less 5 nm. For 5 nm FePt:C nanocomposite thin film with 2 nm FePt underlayer, the coercivity was 8.2 KOe and the correlation length of FePt:C nanocomposite film was 67 nm. These results reveal that the better orientation and magnetic properties for FePt:C nanocomposite films can be tuned by decreasing FePt underlayer thickness.

Granular L10 FePt:X (X = Ag, B, C, SiOx, TaOx) thin films for heat assisted magnetic recording

Ordered L10 FePt thin films are of interest as potential Heat Assisted Magnetic Recording media. In order to achieve the microstructure and magnetic properties to support recording at densities beyond 1 Tbit/in2, it is necessary to add segregants into the FePt films. In this work, the effects of a number of segregants, X, on the microstructure and magnetic properties of FePt:X (X = Ag, B, C, SiO x , TaO x ) thin films, deposited by RF sputtering with various volume content (0–50%), various in-situ heating temperatures (450–600 °C), various Ar pressures (10–40 mtorr) and various sputtering powers (25–200 W) onto 1′′ Si substrates with a MgO texture (002) underlayer (20 nm), were investigated. It was observed that introducing segregants (B, C, SiO x , and TaO x ) into the FePt reduced ordering and grain size of the FePt:X thin films. Ag was found to offset the reduction of ordering in the FePt:X films. The B, SiO x and TaO x promoted columnar growth whereas C promoted a secondary nucleation layer but produced the least reduction of ordering. By varying the volume content of the segregants, the grain size of the FePt:X can be controllably reduced throughout the 2.5–10 nm range. It was found that TaO x produced the best exchange decoupling, thermal durability, grain isolation and hindered grain coalescence as compared with the films deposited with B, C or SiO x . With the FePt:C:Ag films sputtered at 450 °C, a perpendicular coercivity measured at room temperature as high as 25 kOe was achieved; whereas with B, SiO x , and TaO x , perpendicular coercivities as high as 11 kOe were obtained. These FePt:X thin films with small grain size, columnar microstructure and high coercivity are believed to be favorable for application in Heat Assisted Magnetic Recording. The role of surface energies of FePt and the segregant in columnar growth of FePt grains is discussed.

High Temperature Magnetic Properties of Indirect Exchange Spring FePt/M(Cu,C)/Fe Trilayer Thin Films

We report the investigation of temperature dependent magnetic properties of FePt and FePt(30)/M(Cu,C)/Fe(5) trilayer thin films prepared by using magnetron sputtering technique at ambient temperature and postannealed at different temperatures. L10 ordering, hard magnetic properties, and thermal stability of FePt films are improved with increasing postannealing temperature. In FePt/M/Fe trilayer, the formation of interlayer exchange coupling between magnetic layers depends on interlayer materials and interface morphology. In FePt/C/Fe trilayer, when the C interlayer thickness was about 0.5 nm, a strong interlayer exchange coupling between hard and soft layers was achieved, and saturation magnetization was enhanced considerably after using interlayer exchange coupling with Fe. In addition, incoherent magnetization reversal process observed in FePt/Fe films changes into coherent switching process in FePt/C/Fe films giving rise to a single hysteresis loop. High temperature magnetic studies up to 573 K reveal that the effective reduction in the coercivity decreases largely from 34 Oe/K for FePt/Fe film to 13 Oe/K for FePt/C(0.5)/Fe film demonstrating that the interlayer exchange coupling seems to be a promising approach to improve the stability of hard magnetic properties at high temperatures, which is suitable for high‐performance magnets and thermally assisted magnetic recording media.

Structure and magnetic properties of FePt(001) graded films deposited on glass substrates

This study examines L10 FePt (001) hard magnetic films that were coated with a layer having graded perpendicular magnetic constant (Ku) and with a disordered FePt soft layer on glass substrates. The 5 nm-thick hard layer exhibits a clear (001) texture, large perpendicular magnetic anisotropy (PMA), and an island-like morphology with particle size of 15–25 nm. The deposition of the graded or soft layer with a thickness of 5–15 nm does not change the particle size. The graded and hard/soft samples both exhibit reduced out-of-plane coercivity (Hc⊥) but their reversal behaviors differ. Strong exchange coupling appears between the hard and graded layers, maintaining high PMA. However, hard/soft films exhibit weak coupling such that the film becomes in-plane anisotropic when the thickness of the soft layer exceeds 5 nm. The investigations of magnetic domain structures further reveal different magnetic coupling configurations between different types of films. The results herein are consistent with theoretical predictions and are useful for future graded media design.

Reduction of Ordering Temperature of Self-Assembled FePt Nanoparticles by Addition of Au and Ag

The [FePt]94Au6 and [FePt]90Ag10 nanoparticle arrays were synthesized on Si substrates by a reverse micellar method, combined with plasma treatment and in-situ deposition of a SiO2 overlayer, and the post annealing step was performed to drive the face-centered cubic to tetragonal phase transition. These FePt nanoparticles exhibit a quasi-hexagonal order with tailored inter-particle spacing and particle size. The effects of the Ag and Au on the structural and magnetic properties of FePt were investigated. The results indicate that both Au and Ag additives can remarkably enhance the coercivity and reduce the ordering temperature, however, the optimum composition is different for them. The optimum composition is determined to be [FePt]94Au6 and [FePt]90Ag10, respectively, for which the ordering temperature of FePt nanoparticles is reduced by -100 degrees C. After 600 degrees C annealing, the [FePt]94Au6 and [FePt]90Ag10 nanoparticles are totally ferromagnetic with apparent larger coercivities of -7.0 kOe, which is about 3.8 kOe larger than that of the pure FePt nanoparticles. The mechanism of the chemical ordering acceleration may be attributed to the defects and strains caused by the Au/Ag additives.

Interface mediated control of microstructure and magnetic properties of FePt–C thin films

The microstructure and magnetic properties of FePt–C film deposited on the MgO/CrRu underlayer are studied in lieu of carbon doping in FePt and RF biasing assisted etching of the MgO underlayer. Increasing amounts of carbon doping in the FePt deteriorates the chemical ordering as a result of reduced kinetic energy of FePt adatoms due to frequent collision with carbon adatoms. This leads to a reduction in the magnetocrystalline anisotropy energy and hence the coercivity. RF etching of the MgO/CrRu underlayer before deposition of FePt helps to reduce the grain size and intergranular exchange interaction without adversely affecting the chemical ordering. Reduced intergranular exchange interaction leads to an increase in the coercivity.

Nanostructure and magnetic properties of c-axis oriented L10-FePt nanoparticles and nanocrystalline films on polycrystalline TiN underlayers

We performed a systematic study of the nanostructure and magnetic properties of FePt on templates of either (200)-oriented polycrystalline TiN underlayers with in-plane grain sizes from 5.8 to 10 nm (poly-TiN) or highly (200)-textured TiN underlayers epitaxially grown on single-crystalline MgO (100) substrates (epi-TiN). For small nominal FePt thicknesses (0.7–8.0 nm), FePt forms particulate films with the magnetic easy axis perpendicular to the film plane on every template TiN underlayer. In addition, the coercivity of nominally 1.4-nm-thick FePt at 300 K in the out-of-plane direction increases from 5.3 kOe for 5.8-nm-sized poly-TiN to 12.9 kOe for 10-nm-sized poly-TiN and reaches 16.3 kOe for epi-TiN, which shows that the coercivity strongly depends on the degree of the c-axis orientation. For larger FePt nominal thicknesses (16–64 nm), FePt particles percolate and form continuous films, and the direction of the easy magnetic easy axis becomes random. The coercivity of nominally 64-nm-thick FePt at 300 K in the out-of-plane direction is still as large as 8.8 kOe for 10-nm-sized poly-TiN, but it drastically decreases to 0.5 kOe for epi-TiN. The absence of in-plane texture in the FePt layer on the poly-TiN suppresses the decrease in coercivity, which prevents domain-wall displacement.