CoZr Films Research Articles

Angular control of multi-mode resonance frequencies in obliquely deposited CoZr thin films with rotatable stripe domains* *Project supported by the National Natural Science Foundation of China (Grant Nos. 51871117 and 51671099), the Program for Changjiang Scholars and Innovative Research Team in University, China (Grant No. IRT-16R35), and the Gansu Provincial Science Foundation for Distinguished Young Scholars, China (Grant No. 20JR10RA649).

We investigate the angular-dependent multi-mode resonance frequencies in CoZr magnetic thin films with a rotatable stripe domain structure. A variable range of multi-mode resonance frequencies from 1.86 GHz to 4.80 GHz is achieved by pre-magnetizing the CoZr films along different azimuth directions, which can be ascribed to the competition between the uniaxial anisotropy caused by the oblique deposition and the rotatable anisotropy induced by the rotatable stripe domain. Furthermore, the regulating range of resonance frequency for the CoZr film can be adjusted by changing the oblique deposition angle. Our results might be beneficial for the applications of magnetic thin films in microwave devices.

Thickness-dependent resonance frequency of non-uniform procession mode in CoZr stripe-domain magnetic films

The magnetic properties of CoZr magnetic thin films with stripe domains are investigated. The nanocrystalline grain size of 21.2 nm of CoZr thin film was obtained by x-ray diffraction spectra. The rotatable stripe-domain structure of the samples can be clearly observed from the magnetic force microscopy images. From the results of the M–H loop, the typical loops with domain structure of the samples can also be seen. The saturation magnetic fields of the thin films increase as a function of stripe half period in static magnetic properties. In dynamic magnetic properties, we find two precession modes, which include one traditional uniform precession mode with the resonance peak position in the low-frequency band and the other as the non-uniform precession mode with the resonance peak position in the high-frequency band. The ferromagnetic resonance frequencies of the non-uniform procession mode, which are driven by the exchange coupling between adjacent domains, show a decrease in behavior from 5.11to 3.52 GHz in the zero-field dynamic permeability spectra with the stripe domain’s half period increasing, while the ferromagnetic resonance frequencies of the uniform procession mode nearly remain constant. Similar behavior of exchange coupling can be found by analyzing the field-dependent dynamic permeability spectra of CoZr films, which indicates that the main contribution of the thickness-dependent resonance frequency is the exchange coupling between neighboring stripe domains.

Temperature dependence of dynamical permeability characterization of magnetic thin films using shorted microstrip line probe

A temperature dependence microwave permeability characterization system of magnetic thin film up to 10 GHz is designed and fabricated. This system can be used at temperatures ranging from room temperature to 200 °C, and is based on a shorted microstrip probe, which is made by microwave printed circuit board. Without contacting the magnetic thin films to the probe, the microwave permeability of the film can be detected without any limitations of sample size and with almost the same accuracy, as shown by comparison with the results obtained from a shorted microstrip transmission-line fixture. The complex permeability can be deduced by an analytical approach from the measured reflection coefficient of a strip line (S11) with and without a ferromagnetic film material on it. The procedures are the same with the shorted microstrip transmission-line method. The microwave permeability of an oblique deposited CoZr thin film was investigated with this probe. The results show that the room temperature dynamic permeability of the CoZr film is in good agreement with the results obtained from the established short-circuited microstrip perturbation method. The temperature dependence permeability results fit well with the Landau–Lifshitz–Gilbert equation. Development of the temperature-dependent measurement of the magnetic properties of magnetic thin film may be useful for the high-frequency application of magnetic devices at high temperatures.

High Magnetic Anisotropy Field in CoZr Thin Films

Magnetic properties and high frequency characteristics of Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">100-x</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> (x=5-17) thin films have been investigated. The experimental results show that with the increase of Zr content, the saturation magnetization, 4πM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> , decreases from 12.3 kG for x=5 to 7.3 kG for x=17; induced anisotropic field, H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> , of the films increases from 232 Oe for x=5 at first and reaches a maximum value of 266 Oe for x=9; coercivive force along hard and easy direction, H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ch</sub> and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ce</sub> , ranges 1.6-7.1 Oe and 5.4-10.9 Oe, respectively. The highest ferromagnetic resonance frequency, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FMR</sub> of 4.9 GHz could be achieved for the films with x=9. In addition, H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ch</sub> and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ce</sub> are reduced by adopting Cu underlayer or Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">80</sub> underlayer to the studied CoZr films. The optimal magnetic properties of 4πM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> =12 kG , H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ce</sub> =5.4 Oe, H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ch</sub> =0.7 Oe, H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> =258 Oe , ρ = 233 μΩ-cm and <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FMR</sub> =5 GHz are obtained for Co <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">91</sub> Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sub> (110 nm)/Ni <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">20</sub> Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">80</sub> (15 nm) bilayer.

GHz permeability of soft CoZr films: The role of exchange–conductivity coupling

The microwave permeability of CoZr films with different thicknesses is investigated. While Landau–Lifschitz model accounts for the response of the thinnest samples, several peaks are observed on the permeability of thicker layers. A simple model commonly used to account for the permeability of layers in the presence of skin effect is compared to a more sophisticate model taking into account the exchange–conduction coupling. Both models are found to be equivalent. They fail to account for the observed high frequency peaks. Introducing pinning conditions at the interface reproduces qualitatively observed behavior, suggesting the presence of standing spinwaves.

Free-Volume-Dependent Atomic Diffusion in Compositionally Modulated Amorphous Co-Zr Films

Atomic interdiffusion in compositionally modulated amorphous Co-Zr films was investigated by means of in situ X-ray diffraction measurements during successive isothermal annealing. The results were analyzed as free-volume-dependent atomic diffusion and activation-type temperature dependence of both the atomic diffusion coefficient, and the annihilation rates of free volume were confirmed with the activation energy QD=8.84(±0.41)×104 J/mol and QA=3.77(±0.96)×104 J/mol, respectively.

Anisotropy Dispersion and Ferromagnetic Resonance of Amorphous Soft Magnetic Films

Measurement of the anisotropy dispersion using ferromagnetic resonance at radio frequencies has been reconsidered, taking into account the skin effect in relatively thick soft magnetic films. Numerical calculations for 1 μm thick amorphous films showed that eddy current losses are comparable to the resonance absorption. The measured absorption for CoZr film is larger than the calculated absorption under a low bias field, which suggests the eddy current anomaly. In CoZr/SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> multilayered films, the anomaly is reduced. The frequency dependence of the loss part of the permeability is also discussed.

Improved soft magnetism of amorphous CoZr films

Amorphous binary Co 100− x Zr x alloy films have been investigated for high efficiency recording heads. The static and dynamical properties have been improved from extended analysis of the influence of the sputtering parameters and from the use of both a magnetic field applied on the substrate during deposition and a rotating field annealing after deposition which decrease, respectively, the angular dispersion of the easy-axis direction and the anisotropy field. Quasi-ideal CoZr films have been obtained with 4ΠM s = 15.5 kG, H c = 0.02 Oe, H K < 1Oe, λ s < 10 -7, μ' wall = 50000, μ' spin = 1800 an d roll-off frequency F c = 680 MHz.

Formation region of amorphous thin CoZr and CuZr films prepared by cocondensation on hot substrates

The glass formation ranges of thin CoZr and CuZr films condensed on cold and hot substrates (10–800 K) are experimentally determined by X-ray diffraction. The maximum substrate temperatures allowed to condense amorphous films are only slightly below the crystallization temperatures of the amorphous phases. These experimental results are compared with predictions of the glass formation ranges from thermodynamic calculations and instability models. At low substrate temperatures, where no phase separation is possible due to kinetic restrictions, the amorphous phase is favoured in the range between theTo lines which are the stability limits of the extended solid solutions on both sides of a metastable binary phase diagram. For high substrate temperatures, where at least one species of the binary alloy is able to move, the amorphous state can be described to be in a metastable equilibrium with the extended solid solutions neglecting the intermetallic compounds. Therefore, the single-phase amorphous state is restricted to the range between theTml lines which are the metastable liquidus temperatures.

アモルファス軟磁性薄膜の異方性分散と強磁性共鳴

Measurement of the anisotropy dispersion using ferromagnetic resonance at radio frequency has been reconsidered taking into account of the skin effect in relatively thick soft magnetic films. Numerical calculation for 1 μm thick amorphous films shows that the eddy current loss is comparable to the resonance absorption. The measured absorption for CoZr film is larger than the calculated one at low bias field, which suggests the eddy current anomaly. In CoZr/ SiO2 multilayered films, an anomaly is reduced. The frequency dependence of the loss part of the permeability is also discussed.

Brillouin scattering from spin waves in sputtered Co-Zr films

Thermally excited spin waves in thin Co91-Zr9 sputtered films have been studied at room temperature by Brillouin scattering in external magnetic fields of up to 3.5 kOe. In order to precisely determine the g factor and the surface exchange constant, we extensively studied the Damon–Eshbach mode in a 1-μm-thick film. From the slope of the surface magnon frequency in an external magnetic field, the g factor of 2.17±0.04 is determined. The surface exchange stiffness constant Ds has been determined by examining the surface wave-vector dependence on the surface magnon frequency. We obtained a value of Ds =6.9±2.0×10−9 Oe cm2. The best way to determine the bulk stiffness constant is to observe the standing spin waves excited in a thin film whose thickness is less than 200 nm. We could observe scattering from the standing spin waves of up to a third order in a film of 85±5 nm thick. The bulk exchange stiffness constant Db of 2.2±0.4×10−9 Oe cm2 is obtained from the external field dependence of the standing spin-wave frequencies.

Dependence of properties of amorphous Co-Zr films on plasma state in sputtering

Amorphous Co-Zr alloy films with excellent soft magnetism have been prepared by the toroidal plasma (TP) sputtering method. The DC discharge and sputtering characteristics were investigated by applying an additional magnetic field by means of a solenoid coil in order to change the plasma state in sputtering. The applied voltage, discharge current, film thickness, and film composition were found to depend rather strongly on the plasma state. The appropriate magnetic flux could suppress the excessive bombardment of the substrate by gamma -electrons. Amorphous Co-Zr films with excellent soft magnetic properties (e.g. 4 pi Ms of about 16 kG and H/sub c/ of about 0.3 Oe) were deposited on a substrate bombardment by coherent ions from a toroidal plasma. For ions of an appropriate energy, the bombardment improves the soft magnetic properties. This method may be useful for depositing Co-Zr films with high permeability at radio frequency.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Laminated CoZr amorphous thin-film recording heads

Recording heads with four-layer laminated CoZr/Ta films as pole pieces have been fabricated using rf sputter deposition and ion milling techniques. Typical 4πMs of 14 000 G were obtained for CoZr amorphous films compared with 10 000 G for Permalloy films. Recording tests performed with this laminated CoZr/Ta film head indicate 8–12 dB better overwrite than with plated Permalloy film heads having an identical structure. However, the former exhibits a 10%–25% lower amplitude than the latter. This may be attributed to the thermal degradation of the initial permeability μi of the CoZr film during head-fabrication processes. This CoZr/Ta head also shows poorer amplitude stability than the plated Permalloy head.

Uniaxial and local anisotropies in amorphous thin CoZr films

RF sputtered amorphous CoZr and CoNbZr films were field-annealed in vacuum. Their uniaxial and local anisotropies as well as their saturation magnetization were investigated before and after the heat treatment. Susceptibility measurements as introduced by the ripple theory were carried out. In general, the coercive force is very low (0.1 Oe), the saturation magnetization ranges at 1000 emu/cm3for CoZr and 900 emu/cm3for CoNbZr, depending on the composition. The saturation magnetostriction λ s is below 3.10-6. Isothermal hard axis annealing of CoZr films reveals three different sources of the anisotropy: i) a non reversible part with low activation energy, ii) two reversible contributions with different relaxation times.

Induced Magnetic Anisotropy of CoTi and CoZr Amorphous Films

The relaxation process of induced magnetic anisotropy of CoTi and CoZr films is discussed and their permeability compared with that suggested by the single domain theory. The anisotropy energy of the samples was evaluated using the hard and easy axes magnetization curves, and the permeability was measured at 1.4 MHz with the Q meter method. The activation energy of the anisotropy relaxation process in these films was higher than that in CoFeB films, indicating greater thermal stability. The experimental value of the permeability of CoTi films substantially agreed with the predicted values of the single domain theory. A similar results was obtained in CoZr films.

Magnetostriction Constants of High Bs CoZr Amorphous Films

The effect of small amounts of Zr in CoZr films is discussed. It was found that a Zr concentration of 4 at% or less caused the magnetostriction constant to decrease to 1 × 10?6. The magnetostriction constant was measured by making one edge of the film stationary, applying a 20 Oe magnetic field in the easy and hard axis directions and measuring the displacement of the free edges. The magnetorestriction constant of films with a Zr concentration of 4.8 at% and with various film thickness was nearly constant (it was somewhat smaller for thinner films), but after heat treatment this constant decreased without saturating. The value decreased with decreases in the Zr concentration. The magnetostriction constant of CoZr films with a Zr concentration of 3.4 ~ 4 at% decreased to approximately 1 × 10?6.

Magnetic Properties of Co-Based Amorphous Films

The effect of heat treatment on the magnetostriction constants and film stress of CoZr and CoZrTa films was studied. Heat treatment decreased positive magnetostriction constants, while increasing negative magnetostriction constants. Also it was learned that heat treatment converts the compression stress of sputtering into tensile stress. The authors attribute magnetic structural changes to magnetic elastic energy and point out that the magnetostriction constants and film stress are as important in these films as they are in Permalloy films.

Anisotropy Dispersion of Amorphous Co-Metal Films

The effect of heat treatment on the anisotropy dispersion of CoZr films was studied. To induce anisotropy, film samples were annealed using a rotating field (RFA) and a direct field (DFA). The sum of the anisotropy field and the demagnetizing field of the DFA film (11.5 Oe) corresponded well with the value of the magnetic field of the distribution peak. The DFA ΔQ half value of less than ±10° indicates a well aligned anisotropy, but the anisotropy of RFA films was dispersed in all directions. The initial anisotropy of these RFA films did not sufficiently relax under the annealing conditions, but prolonging RFA increases the peak width and dispersion and may decrease the macroanisotropy. The anisotropy dispersion of CoFeB and CoTi films is about the same.

Magnetic properties of CoZr amorphous films prepared by low energy ion beam sputtering

In this paper, magnetic properties of CoZr amorphous films prepared using low-energy ion-beam sputtering are investigated by varying the accelerator voltage and beam current of a single-grid ion-beam sputtering system. It is shown that CoZr films become amorphous with a lower Zr content when the films are prepared with lower accelerator voltage or lower ion-beam current. It is also clarified that the saturation magnetostriction constant of amorphous CoZr film becomes smaller as the Zr content becomes smaller ; a film with a Zr content of approximately 3.3at% has a magnetostriction constant of zero without adding a third element such as Nb, Ta or Re. CoZr amorphous films with a saturation magnetization of more than 1.5T, a coercive force of less than 0.2Oe and a magnetostriction constant of zero could be obtained using low-energy ion-beam sputtering with an accelerator voltage of less than 300V.

Induced anisotropy of Co-Zr and Co-Ti amorphous films

The relaxation process of induced anisotropy has been investigated in Co-Zr and Co-Ti sputtered films. For the analysis of the process, the films have been annealed isothermally in a static magnetic field after annealing in a rotating field. The relaxation curves have been fitted with calculated ones assuming the distribution of the activation energy. The mean values of the activation energy and their distribution have been estimated at (2.1±0.2)eV for Co 88 Zr 12 and (1.8±0.2)eV for Co 83 Ti 17 films, respectively. The relation between effective permeability and the uniaxial anisotropy can be well explained by the single domain theory.