James O. Rantschler

Frequency- and time-resolved measurements of FeTaN films with longitudinal bias fields

The high frequency characteristics of 100 nm FeTaN films have been studied by using both time-resolved inductive techniques and frequency-resolved permeability measurements. Experiments performed as a function of longitudinal bias fields from 120 to 2400 A/m (1.5–30 Oe) showed precessional frequencies from 1.3 to 2.5 GHz, initial permeabilities from 1600 to 500, and damping constants α=0.013 to 0.0045. It is illustrated that the magnetization precessional data obtained from the time-resolved inductive technique can be Fourier transformed to the frequency domain to give the real and imaginary components of a permeability spectrum; this spectrum compares well with data obtained from frequency-resolved permeability measurements. It is also demonstrated that accurate values of the damping constant α can only be determined from permeameters whose bandwidth is two to three times the ferromagnetic resonance frequency of the material to be measured.

Structure, stress, and magnetic properties of high saturation magnetization films of FeCo

Thin (/spl sim/2000 /spl Aring/) films of Fe/sub 60/Co/sub 40/ have been prepared by sputtering on Si/SiO/sub 2/, Si/AlO/sub x/, AlTiC/AlO/sub x/, AlTiC/AlO/sub x//NiFe, and AlTiC/AlO/sub x//NiFeCr substrates using an alloy Fe/sub 60/Co/sub 40/ target. The structure of the films was characterized by means of X-ray diffraction and transmission electron microscopy (TEM). Surface roughness was characterized by atomic force microscopy (AFM). Stress, transport, and magnetic measurements were conducted. We observed correlation in the following pairs of properties: coercivity-stress, grain size-stress, and coercivity-grain size. Although individual films had a stress in the wide range of compressive 2.5/spl times/10/sup 10/ Dyne/cm/sup 2/ to tensile 1.3/spl times/10/sup 10/ Dyne/cm/sup 2/, which depended to some degree on the material of the substrate and underlayer, we found that biaxial stress and coercivity seem to be described by a general trend, with coercivity being as low as 19 Oe at intermediate tensile stress and as high as 225 Oe at high compressive stress. The unstrained lattice parameter and Youngs modulus of the alloy Fe/sub 60/Co/sub 40/ were also determined.

Ripple field effect on high-frequency measurements of FeTiN films

Ferromagnetic resonance and permeability linewidths of high-moment FeTiN thin films have been recorded and analyzed using ripple theory in order to separate inhomogeneous broadening from the intrinsic damping of the material. These results are compared to the analysis of the same phenomenon using a simple but common model of amplitude dispersion. The ripple is also used to analyze the behavior of the resonance frequency of a sample when rotated in low fields.

Microstructure and damping in FeTiN and CoFe films

Thermally stable films of FeTiN, have been prepared and characterized by ferromagnetic resonance, x-ray diffraction, x-ray photoelecton spectroscopy, and magnetostriction measurements to determine the relationships between the microstructure and the damping constants. The resonance studies were carried out at multiple frequencies to determine the intrinsic damping constant, α, and the extrinsic damping constant, ΔH0, as well as values of the anisotropy field, Hk, the gyromagnetic ratio, γ, and the saturation magnetization value, 4πMs. Data from similar experiments on CoFe films were compared with the FeTiN data. Our results show no relationship between intrinsic damping and the magnetostriction, but a strong dependence of the extrinsic constant on the grain size.

Interface coupling and magnetic properties of exchange-coupled Ni81Fe19/Ir22Mn78 bilayers

Hysteresis loop measurements using magnetooptic Kerr effect magnetometry in the low frequency region and magnetization dynamics measurements using high frequency permeametry are carried out to study the exchange anisotropy in Ni81Fe19/Ir22Mn78 bilayers. These two measurement techniques provide different exchange anisotropies for bilayers with thin Ir22Mn78 films. The observations can be understood by assuming that the AF grains break into domains due to the interface random field. By analysing the results from these two techniques, the interface coupling strength and the magnetic properties of the bilayers can be quantitatively determined.

Damping at normal metal/permalloy interfaces

We have determined the Gilbert damping parameter as a function of layer thickness in six sets of samples with either a normal metal (NM)/Permalloy (NiFe) or NM/NiFe/NM structure by measuring the ferromagnetic resonance (FMR) linewidth for all series and correcting for extrinsic broadening effects. In the NM/NiFe samples, we find that increasing the interface roughness increases the damping quadratically from 0.01 at 3 nm to 0.11 at 47 nm, and by controlling the roughness of the copper layer, we have found there is no evidence of increased damping due to the thickness of the copper layer between 100-2050 nm of copper.

High-frequency behavior of electrodeposited Fe-Co-Ni alloys

In this paper, we investigate the high frequency behavior and damping of the FeCoNi films as a function of their composition and microstructure.FeCoNi alloys have been demonstrated to have a low coercivity and high saturation magnetisation.

Magnetic and thermal properties of IrMn/FeTaN films

The antiferromagnetic–ferromagnetic exchange coupling between IrMn and FeTaN films has been investigated to study the effects of the exchange field on the high frequency response and the thermal stability of the anisotropy field of FeTaN. Ferromagnetic resonance, vibrating sample magnetometer, and torque measurements were used to determine the values of the unidirectional exchange bias field Hp, the uniaxial anisotropy field Hk and the interfacial energy J. Permeameter measurements to 3 GHz were used to study the effect of the exchange field on the low-frequency permeability and the high-frequency cutoff. Measurements on varying thicknesses of IrMn and FeTaN films gave Hp values from 4 to 115 Oe, Hk values from 10 to 20 Oe, Hc values from 10 to 20 Oe, and an interfacial energy J=0.075u200aergs/cm2. The exchange coupling was found to have significant effects on the permeability and the thermal stability of the anisotropy.

Dynamic measurement of the thermal stability of the magnetic anisotropy in FeTaN films

In earlier publications it has been shown that the value and direction of the magnetic anisotropy in FeTaN films can be changed by thermal annealing in a dc magnetic field. These films have potential as future write head materials, and this type of instability could pose a problem. In the current work dc and ac annealing experiments have been performed to test the stability of the anisotropy. Our results confirm the model of interstitial-nitrogen-induced anisotropy in the FeTaN films by illustrating that the magnitude of the anisotropy is reduced at higher temperatures, and that the direction of the anisotropy is stable if the time in the switched direction is less than the time required for diffusion of the nitrogen to a different interstitial position. The direction is stable at 100u200a°C, for square wave magnetic field switching between the easy and hard axes, at frequencies above 500 Hz. The direction is unstable at 100u200a°C for switching between the hard axes at frequencies less than 5 kHz.

Testing damping formalisms with microwave permeability

In this paper, we report experimental evidence that this form of the dissipation requires additional damping mechanisms in order to explain well-known phenomena, based upon the observed difference between the peak /spl omega//sub p/ and zero-crossing /spl omega//sub 0/ frequencies of magnetic permeability data.