In-plane Uniaxial Anisotropy Field Research Articles

Piezoelectric control of magnetic dynamics in Co/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure

A microstrip method with vector network analyzer was used to investigate electric field control of magnetic dynamic properties in Co/Pb(Mg1/3Nb2/3)O3-PbTiO3 heterostructure at room temperature. Under external electric field, the natural resonance frequency and permeability of the Co film were found to modulate between 1.8–2.8 GHz and 50–150, respectively. In addition, the in-plane uniaxial magnetic anisotropy field can also be electrically tuned from 54 to 170 Oe, while the ferromagnetic resonance field was substantially enhanced about 350 Oe as well. Such an improvement of magnetic anisotropy is desirable for effectively electric control of resonance frequency and permeability in low energy microwave devices.

Microwave ferromagnetic properties of as-deposited Co2FeSi Heusler alloy films prepared by oblique sputtering

The Co2FeSi films are deposited on Si (100) substrates by an oblique sputtering method at ambient temperature. It is revealed that the microwave ferromagnetic properties of Co2FeSi films are sensitive to sample position and sputtering power. It is exciting that the as-deposited films without any magnetic annealing exhibit high in-plane uniaxial anisotropy fields in a range of 200 Oe–330 Oe (1 Oe = 79.5775 Am−1), and low coercivities in a range of 5 Oe–28 Oe. As a result, high self-biased ferromagnetic resonance frequency up to 4.75 GHz is achieved in as-deposited oblique sputtered films. These results indicate that Co2FeSi Heusler alloy films are promising in practical applications of RF/microwave devices.

High-Frequency Ferromagnetic Properties of Nanocrystalline (Co<sub>2</sub>FeSi)<sub>1-x</sub>(Al<sub>2</sub>O<sub>3</sub>)<sub>x </sub>Heusler Alloy Films with Uniaxial Magnetic Anisotropy

A series of (Co2FeSi)1-x(Al2O3)xHeusler alloy films with various Al2O3-doping were prepared by an oblique sputtering method. It is exciting that the as-deposited films exhibit a very high in-plane uniaxial magnetic anisotropy (UMA) field up to 360 Oe and low coercivity of 12 Oe. Consequently, a very high self-bias ferromagnetic resonance frequency in excess of 5.02 GHz was obtained in as-deposited Co2FeSi films without any annealing. The good microwave ferromagnetic performances and the integrated circuits compatible fabrication process of Co2FeSi films make possible application in RF/microwave devices.

Influence of substrate temperature on high-frequency soft magnetic properties of [Fe80Ni20–O/NiZn–ferrite]n multilayer thin films

In this research, a series of [Fe80Ni20–O/NiZn–ferrite]n multilayer thin films were prepared by magnetron sputtering at different substrate temperatures. The influences of NiZn–ferrite interlayer and substrate temperature on high-frequency soft magnetic properties of [Fe80Ni20–O/NiZn–ferrite]n multilayer thin films were investigated. It was found that the saturation magnetization was highly dependent on the substrate temperature during the sputtering procedure. By increasing the substrate temperature from room temperature to 300°C, the saturation magnetization increased from 7.34kG to maximum of 9.26kG at 150°C, and then decreased to 6.53kG at 300°C. The adjustment of substrate temperature is essential to obtain the low coercivity, high permeability and controllable in-plane uniaxial magnetic anisotropy field of the multilayer thin films.

Magnetic properties of (Co92Zr8/SiO2)15 multilayer thin films for GHz applications

Abstract In this work, the static and microwave magnetic properties of (Co 92 Zr 8 /SiO 2 ) 15 multilayer thin films were investigated. The in-plane uniaxial anisotropy field can be tailored from 120 to 170 Oe by adjusted the thickness of SiO 2 from 10 to 1 nm, and the resonance frequency can be tailored from 3.47 to 3.87 GHz correspondingly. This work provided a kind of magnetic/dielectric multilayer thin films with adjustable magnetic properties for microwave application.

Thermal Stability of the Ferromagnetic In-Plane Uniaxial Anisotropy of Fe-Co-Hf-N/Ti-N Multilayer Films for High-Frequency Sensor Applications

In this study, the thermal stability of the in-plane uniaxial anisotropy field of Fe32Co44Hf12N12/Ti50N50 multilayer films was investigated from room temperature up to 500 °C with regard to contactless high-frequency sensor applications. The uniaxial anisotropy field of about μoHu ≈ 5 mT was thermally induced by annealing the films in a static magnetic field of 50 mT in vacuum for one hour either at an annealing temperature of Tα = 400 °C or Tα = 600 °C. The films which were annealed at Tα = 600 °C show a clear distinction between the easy and hard axis of polarization up to temperatures of 500 °C. Hence, the uniaxial anisotropy, thermally induced at Tα = 600 °C, is stable at working temperatures up to 500 °C. In contrast, films with a uniaxial anisotropy induced at Tα = 400 °C show a different behavior. Here, hysteresis loop measurements indicate that above a working temperature of 200 °C the uniaxial anisotropy field turns away from its direction at room temperature. In conclusion, only the Fe32Co44Hf12N12/Ti50N50 multilayer films with a uniaxial anisotropy field induced at Tα = 600 °C promise a great potential for contactless high-frequency sensor applications up to 500 °C.

NiFe 박막의 두께에 따른 강자성 공명 특성 분석

본 연구에서는 NiFe 박막 시편을 마그네트론 스퍼터링 방법으로 제조하여 박막면 기준으로 수직면(out-of-plane) 자기장 방향과 수평면(in-plane) 자기장 방향에 따른 강자성 공명 자기장을 측정하였다. 수직면 자기장 방향에 따른 강자성 공명 자기장으로부터 유효자화량(<TEX>$M_{eff}$</TEX>)을 도출하였으며, NiFe 두께에 따른 <TEX>$M_{eff}$</TEX>의 감소는 <TEX>$K_s=-0.23\;erg/cm^2$</TEX>의 값을 갖는 표면 이방성 상수에 기인하였다. 또한 수평면 자기장 방향에 따른 강자성 공명 자기장으로부터 수평면에서의 일축 이방성 자기장을 도출하였다. 한편, 일축 이방성 에너지의 자화 용이축이 두께가 감소함에 따라 시편 제조 시 인가한 자기장의 반대 방향으로 회전하고 있었으며, 이러한 현상은 시편 표면에 형성된 NiFeO의 반강자성 특성에 의한 현상으로 설명하였다. The out-of-plane and in-plane angular dependence of ferromagnetic resonance field was measured in NiFe thin films fabricated by magnetron sputtering. The effective magnetization was obtained from the out-of-plane angular dependence of ferromagnetic resonance field, which was well agreed with calculated one. The decrease of effective magnetization with NiFe thickness was due to the surface anisotropy constant of <TEX>$K_s=-0.23\;erg/cm^2$</TEX>. The in-plane uniaxial anisotropy fields were obtained from the in-plane angular dependence of ferromagnetic resonance field. The easy axis of in-plane uniaxial anisotropy field was rotated to the reverse direction of applied magnetic field during sample fabrication, which was explained by the antiferromagnetic NiFeO layer at sample surface.

Soft magnetic property and high-frequency permeability of [Fe80Ni20–O/TiO2]n multilayer thin films

Multilayer thin films with excellent magnetic property and high-frequency permeability possess a significant position in electromagnetic miniaturization devices applied in GHz range. In this work, by controlling the alternately magnetron sputtering time at room temperature, we fabricated [Fe80Ni20–O/TiO2]n multilayer thin films with different TiO2 interlayer thicknesses (t = 0.25–4 nm) and fixed Fe80Ni20–O layer thickness without applying inducing magnetic field. The static and dynamic magnetic properties of these films were investigated and evident in-plane uniaxial magnetic anisotropy field can be adjusted in a broad range only by changing the thickness of the TiO2 interlayer. When the t increases gradually from 0.25 to 4 nm, the resistivity and in-plane uniaxial magnetic anisotropy field increase monotonically. In particular, by controlling the thickness of each TiO2 interlayer to an optimized value, good soft magnetic property and high-frequency performances in GHz range have been observed.

Microwave magnetic properties of the oriented CoIr soft magnetic film with negative magnetocrystalline anisotropy

The natural resonance frequency of the oriented soft magnetic thin film with in-plane uniaxial anisotropy and negative magnetocrystalline anisotropy (Kugrain) was investigated in hcp structure of Co80Ir20 film with the c-axis perpendicular to the film plane. As the out-of-plane anisotropy field contained the field produced by negative Kugrain besides the demagnetization field, the natural resonance frequency was enhanced dramatically compared with the conventional soft magnetic film without magnetocrystalline anisotropy. Through solving the equation of magnetization precession, the initial permeability of this kind of film was shown to be unrelated to the negative Kugrain and yet determined by the in-plane uniaxial anisotropy field and the saturation magnetization of the film.

Fe80Ni20–O/SiO2]n Multilayer thin films for applications in GHz range

Thin film materials with excellent high-frequency, magnetic and electrical properties are in great demand in modern electromagnetic devices operating in GHz range. In this letter, we fabricated [Fe80Ni20–O/SiO2]n multilayer thin films with different SiO2 interlayer thicknesses (t=0.5–4nm) and fixed Fe80Ni20–O layer thickness by controlling the sputtering time at room temperature. In these films, the in-plane uniaxial magnetic anisotropy fields can be adjusted in a broad range (from 26 to 107Oe) by just changing the thickness of each SiO2 interlayer without applying any inducing field. Excellent high-frequency performances in GHz range have been observed in the typical sample.

Magnetic anisotropy in isotropic and nanopatterned strongly exchange-coupled nanolayers

In this study, the fabrication of magnetic multilayers with a controlled value of the in-plane uniaxial magnetic anisotropy field in the range of 12 to 72 kA/m was achieved. This fabrication was accomplished by the deposition of bilayers consisting of an obliquely deposited (54°) 8-nm-thick anisotropic Co layer and a second isotropic Co layer that was deposited at a normal incidence over the first layer. By changing the thickness value of this second Co layer (X) by modifying the deposition time, the value of the anisotropy field of the sample could be controlled. For each sample, the thickness of each bilayer did not exceed the value of the exchange correlation length calculated for these Co bilayers. To increase the volume of the magnetic films without further modification of their magnetic properties, a Ta spacer layer was deposited between successive Co bilayers at 54° to prevent direct exchange coupling between consecutive Co bilayers. This step was accomplished through the deposition of multilayered films consisting of several (Co8 nm-54°/CoX nm-0°/Ta6 nm-54°) trilayers.

Tunable resonance frequency of FeNi films by oblique sputtering

FeNi thin films were fabricated by radio frequency magnetron sputtering on Si(111). Dynamic properties at remanence of the films were systematically investigated in a wide frequency range from 100MHz to 5GHz. The results show that both thickness of FeNi films and oblique angle have important effects on the magnetic properties of the films, the magnetic resonant frequency of the films can also be adjusted by the two factors. The in-plane uniaxial magnetic anisotropy field can be adjusted from 82Oe to 220Oe by increasing the oblique angle. As a consequence, the magnetic resonant frequency of the films increased from 2.7GHz to 4.2GHz.

High frequency characteristics of FeCoAlO thin films fabricated with asymmetric target at different Ar gas flow rates

FeCoAlO thin films with good soft magnetic properties were fabricated by using RF magnetron sputtering. In order to obtain good high-frequency performance, the in-plane uniaxial anisotropy was tuned by combining the effects of in situ magnetic field and the gradient of Al–O concentration. The composition gradient was controlled by using an asymmetric target and different Ar gas flow rates changing from 5 sccm to 17.5 sccm. It was found that at the range of Ar gas flow rate from 7.5 sccm to 15 sccm, the films showed an excellent high-frequency performance: the resonance frequency was beyond 3.0 GHz and the real permeability μ′ had a high value of ∼200 at low-frequency side. In particular, the film prepared at the Ar gas flow rate of 15 sccm showed a resonance frequency of 4.0 GHz. Large resonance frequency can be attributed to the high in-plane uniaxial anisotropy field which was induced by stress and the external magnetic field. The high values of permeability and resonance frequency enable the FeCoAlO thin films to be one of the important candidates for microwave applications.

Soft Magnetic Property of [Fe&lt;sub&gt;80&lt;/sub&gt;Ni&lt;sub&gt;20&lt;/sub&gt;-O/ZnO]&lt;sub&gt;&lt;i&gt;n&lt;/i&gt;&lt;/sub&gt; Multilayer Thin Films for High-Frequency Application

A series of [Fe80Ni20-O/ZnO]nmultilayer thin films with different ZnO separate layer thicknesses (t, from 0 to 3 nm) and fixed Fe80Ni20-O layer thickness (about 5 nm) have been fabricated on (100)-oriented silicon wafers and glass substrates by reactive magnetron sputtering. Microstructure analysis and static magnetic measurement results indicate that the magnetic properties of the films can be adjusted by the variation of ZnO monolayers thickness. All films reveal an evident in-plane uniaxial magnetic anisotropy (IPUMA). The values of in-plane uniaxial magnetic anisotropy fields (Hk) and resistivity (ρ) can be changed from 8 to 57 Oe and 62 to 168 μΩ•cm respectively with the t increasing. While the values of hard axis coercivity (Hch) and easy axis coercivity (Hce) reveal minimums of 1.5 and 3 Oe respectively at t = 1 nm.

Magnetic Properties of Oxygen-doping Fe-Co-based Nanocrystalline Alloy Films for High Frequency Application

The effects of the introduction of oxygen were studied on the Fe62Co32Cr6–O alloy films synthesized by magnetron co-sputtering. The as-deposited films exhibited a high saturation magnetization and a suitable in-plane uniaxial anisotropy field at an optimized condition of an oxygen gas flow ratio of 1.3%. Also, a high real permeability of ∼200 at frequency up to 3.3GHz was obtained from the microwave permeability measurement at the optimized condition above. The combination of high saturation magnetization, adjustable in-plane uniaxial magnetic anisotropy field, and high resistivity makes the Fe62Co32Cr6–O films become a promising candidate for the high-frequency applications.

Thickness dependence of microwave magnetic properties in electrodeposited Fe–Co soft magnetic films with in-plane anisotropy

In this work, the thickness effect of Fe 52Co 48 soft magnetic films with in-plane anisotropy on static and microwave magnetic properties was investigated. The hysteresis loop results indicated that the static in-plane uniaxial anisotropy field increased from almost 0–60 Oe with increasing film thickness from 100 to 540 nm and well-defined in-plane uniaxial magnetic anisotropy can be obtained as the thickness reached 540 nm or larger. Based on Landau–Lifshitz–Gilbert (LLG) equation, the microwave complex permeability spectra were analyzed and well fitted. The LLG curve-fitting results indicated that the initial permeability increased from 106 to 142 and the resonant frequency was shifted from 4.95 to 4.29 GHz as the film thickness was varied from 540 to 1500 nm. Moreover, it was found that there was a discrepancy between the static and the dynamically determined anisotropy field, which can be explained by introducing an additional effective isotropic ripple field. The decreased ripple field was suggested to result in a significant decrease of damping coefficient from 0.109 to 0.038.

On the comparison of the polarisation behaviour of exchange-biased AF/F NiMn/Fe37Co48Hf15 bi-layer and multi-layer films with increased ferromagnetic cut-off frequencies

Antiferromagnetic/ferromagnetic (AF/F) NiMn/Fe37Co48Hf15 films were investigated with respect to their exchange bias, in-plane unidirectional anisotropy, polarisation and high frequency behaviour. After deposition, carried out by r.f. magnetron sputtering, the films were post-annealed for 4h at 300°C in a static magnetic field, in order to induce exchange-bias, which results in a unidirectional anisotropy. Dependent on the presence of a bi-layer or multi-layer sandwich structure the films show a different exchange-bias field–ferromagnetic inter-layer thickness behaviour with exchange-bias fields μ0⁎Heb between 2 and 10mT. The in-plane uniaxial (single film) or unidirectional anisotropy fields μ0*HUF were between 4 and 18mT. This results in a significant increase of the cut-off frequency in the GHz range in comparison to a single Fe37Co48Hf15 film, which is shown by frequency-dependent permeability plots. High damping in the imaginary part of the permeability, i.e., high resonance line broadening could be observed for films with high coercivity μ0*Hc of around 7mT in the easy axis of magnetisation.

Method to improve high-frequency magnetic characteristics of Fe 80Ni 20–O alloy films by introducing low-dose oxygen

In this letter, we propose a method to fabricate Fe 80Ni 20–O film with improved static and high-frequency, magnetic and electrical properties. Fe 80Ni 20–O alloy films were prepared by direct current magnetron sputtering at room temperature. The results show that the in-plane uniaxial magnetic anisotropy fields can be adjusted in a broad range by solely adding a very low dose of oxygen into Fe 80Ni 20 alloy films without applying any inducing field on substrates during deposition. By increasing the oxygen flow ratio from 0.75% to 3%, Fe 80Ni 20–O alloy films could be achieved with an adjustable ferromagnetic resonance frequency f r (from 2.2 to 5.9 GHz), a large saturation magnetization 4πMs (from 16.7 to 15.2 kG), and a high resistivity ρ (from 56.7 to 108 μΩ cm).

Tunable cut-off frequency by in-plane uniaxial anisotropy in (Fe66.9Co33.1)86.8Sm13.2 films

(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.

Magnetic Properties of Fe-Co Films with Tuneable In-Plane Uniaxial Anisotropy Prepared by Electrodeposition

Fe-Co soft magnetic films with tuneable in-plane uniaxial anisotropy were successfully electrodeposited onto ITO conductive glass. The influence of composition and electrolyte temperature on in-plane magnetic anisotropy field was investigated. Our results show that the in-plane uniaxial anisotropy can be induced by a magnetic field applied in the film plane during electrodeposition. Fe-Co films with various Fe content in the range from 35 at.% to 53 at.% were obtained and the magnetic anisotropy field was very sensitive to the composition. Moreover, the influence of electrolyte temperature on magnetic anisotropy field was investigated and it was found that the in-plane uniaxial anisotropy field can be tuned by varying the electrolyte temperature from 5 to 40 oC.