K. M. Kemner

Extended x‐ray‐absorption fine‐structure studies of heat‐treated fcc‐Fe50Cu50 powders processed via high‐energy ball milling

The local structure and chemistry of a ferromagnetic fcc‐Fe50Cu50 solid solution obtained through high‐energy ball milling were measured before and after heat‐treatment‐induced decomposition using extended x‐ray‐absorption fine‐structure measurements. The decomposition is first evident with the phase separation of α‐Fe after a heat treatment at 523 K. Analysis of the residual fcc component revealed that the Fe atoms were predominantly surrounded by other Fe atoms, suggesting that the Fe has coalesced within the fcc structure. The Fe atoms within the fcc phase likely exist in low‐spin clusters which provide an explanation for the reduced values of low‐temperature magnetization previously measured in annealed samples [P. Crespo et al., Phys. Rev. B 48, 7134 (1993)].

Polarization-dependent EXAFS studies of chemical and structural anisotropy in sputter-deposited Co/sub 78/Cr/sub 22/ films

Extended x-ray absorption fine structure measurements of a Co/sub 78/Cr/sub 22/ film were performed using normal and glancing incident radiation in order to investigate, respectively, the in-plane and out-of-plane local structure and chemistry. The Fourier transformed EXAFS data illustrates the presence of an anisotropy between the in-plane and out-of-plane structures around Co and Cr atoms. Analysis of the local environments around Co for the two sample orientations indicates the presence of Co-rich clusters, while fitting of the Cr environment indicates preferential ordering parallel to the film plane. These results are consistent with earlier reports of a high density of stacking faults perpendicular to the growth axis, supporting the interpretation that a platelet-like texturing exists within the columnar microstructure. Cr segregation parallel to the film plane provides diffusion paths allowing for transverse compositional inhomogeneities observed in TEM studies. >

The role of Ta and Pt in segregation within Co‐Cr‐Ta and Co‐Cr‐Pt thin film magnetic recording media

Polarization dependent extended x‐ray absorption fine structure (PD‐EXAFS) and magnetic circular dichroism (MCD) measurements of CoCrTa and CoCrPt films, sputter deposited at varying substrate temperatures, were performed to investigate the average local structure and chemistry about the Ta, Pt, and Co atoms and the average magnetic moment of the Co and Cr atoms within these films. Results from the MCD measurements indicate the average net magnetic moment of the Cr atoms is opposite in direction and five percent in amplitude relative to the Co moments. Inspection of the Fourier transforms of the XAFS data from these samples shows an increase in structural disorder around the Ta and Pt atoms with increasing substrate deposition temperature. A further comparison between the Ta and Pt edge EXAFS results show that the temperature‐dependent increase in structural disorder is greater around the Ta atoms in the CoCrTa system than it is around the Pt atoms in the CoCrPt system.

Preferential site distribution of Pt and Ta in CoCr-based films: An extended x-ray absorption fine structure study

Co86Cr12Ta2, and Co86Cr12Pt2 films were made to investigate the local structure and chemistry around Ta and Pt atoms to determine their site distributions in these alloys. Comparisons between the measured data and data collected from experimental standards and calculated using theoretical EXAFS simulation codes indicate that the Ta atoms are preferentially distributed to the Cr-enriched regions of the CoCr media, and the Pt atoms have an effect on the local environment of the Co atoms. Both Ta and Pt introduce a large amount of local structural disorder to the local environments in which they reside. The presence of Ta atoms in the Cr-enriched regions further reduces the magnetization of these regions, which enhances the magnetic isolation of the Co regions from each other. This helps improve the noise characteristics of the films. The portion of the Pt atoms residing in the Co-enriched regions increases the magnetic anisotropy of the films, thereby increasing their coercivity.

Direct observation of Cr magnetic order in CoCrTa and CoCrPt thin films

Magnetic circular dichroism measurements of room temperature, sputter deposited Co86Cr12Ta2 and Co86Cr12Pt2 films were performed to investigate the local magnetic ordering of the Co and Cr atoms. The results demonstrate that the Cr has a net magnetic moment and that a small fraction of the Cr is magnetically oriented opposite to the Co moment.

Giant magnetic effects in the L‐edge extended x‐ray absorption fine structure of 3d transition metals

A systematic extended x‐ray absorption fine structure (EXAFS) study at the L edges of ferromagnetic Fe, Co, and Ni thin films has been conducted using circular polarized soft x rays. A very large helicity dependence has been observed in the L‐edge EXAFS spectra. Surprisingly, in contradiction with prior works, these magnetic EXAFS results indicate a nonlinear dependence of this effect on the magnetic polarization of the scattering atom. The data further indicate that the dominant scattering paths responsible for the effect are different from those responsible for EXAFS. A discussion of the results in relation to the present understanding of the underlying mechanism and its ramifications to the existing theoretical frameworks is also presented.

Structure and magnetism in fcc magnetic transition metals on (001) diamond (abstract)

We have prepared single crystal face centered cubic (fcc) magnetic transition metal films (Co,Ni,Fe) on (001) diamonds, the thickness of the films varying between a few tenths of a nanometer to over 100 nm. The crystalline quality and fourfold symmetry of these layers was monitored in situ during the film growth with RHEED and a chemical analysis was performed using Auger spectroscopy. In addition, the structure of the samples was investigated exu2009situ using X‐ray diffraction and EXAFS, demonstrating the single crystal, fcc (001) structure throughout each entire film. The magnetic characterization was performed with Ferromagnetic Resonance (FMR) and Superconducting Quantum Interference Device (SQUID) hysteresis loops. The saturation magnetization of the Co films is only slightly lower than the literature values. The coercive fields are very small (∼25 Oe) and the magnetization reversal very sharp. The FMR yielded a fourfold anisotropy comparable to literature values. The observation of the first standing s...

Polarization-dependent XAFS studies on the role of Ta in the compositional segregation of Co-Cr-Ta magnetic recording media

Extended X-ray absorption fine structure (EXAFS) measurements of Ta in Co-Cr-Ta films were performed using normal glancing incident radiation in order investigate, respectively, the in-plane and out-of-plane local structure and chemistry about the Ta atom sites. The Fourier transformed EXAFS data illustrates the presence of an anisotropy between the in-plane and out-of-plane structures around the Ta atoms, indicating that the Ta atoms are incorporated in a closed-packed structure with the c-axis aligned in the plane of the film. Analysis of the local environments around Ta indicates that the Ta atoms are either randomly distributed throughout the film or have preferentially segregated to the Cr-rich regions. Results indicate that an increase in temperature results in Ta having a broader distribution of first-neighbor distances as well as a slight decrease in the number of surrounding atoms. This is consistent with a local structure model which has vacancies preferentially segregating to the Ta atoms thereby decreasing the diffusion of Cr within the grains.

Exafs studies and simulations of local anisotropy in Co-Cr films

Extended x-ray absorption fine structure measurements of a Co78Cr22 film were performed using normal and glancing incident radiation in order to investigate, respectively, the in-plane and out-of-plane local structure and chemistry. The Fourier transformed EXAFS data of the in-plane and out-of-plane structures around the Co and Cr atoms illustrates the presence of an anisotropy. Analysis of the local environments around Co for the two sample orientations indicates the presence of Co-enriched clusters, while similar studies of the Cr environments indicate preferential ordering parallel to the film plane. Quantitative analysis of the higher order Fourier transform peaks shows a greater amount of disorder perpendicular to the film plane beyond that expected for a textured hcp film. These results are consistent with earlier reports of a high density of stacking faults or twinning planes perpendicular to the growth axis, supporting the interpretation that a platelet-like texturing exists within the columnar microstructure.

Polarization‐dependent extended x‐ray absorption fine structure measurements of metastable fcc Co on (100) diamond

Polarization‐dependent extended x‐ray absorption fine structure (EXAFS) measurements have been made on a single‐crystal 1000 A thick Co film deposited on (100) diamond. By comparing the EXAFS signals corresponding to the in‐plane and out‐of‐plane structure relative to the film plane, we clearly illustrate that the film exists in the face centered cubic (fcc) phase. An analysis of the first shell Fourier transform peaks for the in‐plane and out‐of‐plane structure surrounding the Co atoms indicates that the majority of the fcc Co crystal lattice is not distorted, demonstrating that the majority of film is relaxed and not pseudomorphic.