Paul C. Dorsey

Pulsed laser deposition of epitaxial BaFe12O19 thin films

Epitaxial thin films of barium hexaferrite (BaFe12O19) have been fabricated by the pulsed laser deposition technique on basal plane sapphire. Structural studies reveal the films to be predominantly single phase and crystalline, with the c axis oriented perpendicular to the film plane. The magnetic parameters deduced from vibrating sample magnetometer and ferromagnetic resonance (FMR) measurements are close to the parameters associated with bulk materials. Post annealing of the films reduced the FMR linewidth by more than a factor of 3 so that it compares reasonably well with single‐crystal films. The derivative FMR linewidth was measured to be 66 Oe at 58 GHz and 54 Oe at 86 GHz. Spin‐wave‐like modes have been observed for the first time in barium ferrite films. The deduced exchange stiffness constant of 0.5×10−6 ergs/cm is in reasonable agreement with recent calculations.

Epitaxial yttrium iron garnet films grown by pulsed laser deposition

Epitaxial Y3Fe5O12 (YIG) films have been grown by the pulsed laser deposition (PLD) technique on (111) gadolinium gallium garnet substrates. The effect of substrate temperature and oxygen partial pressure on the structure, composition, and magnetic properties of the films was investigated and compared to liquid phase epitaxy YIG films. The results demonstrated that epitaxial YIG films could be prepared under a wide range of deposition conditions, but narrow linewidth (ΔH≂1 Oe) films were producible only at low oxygen partial pressures (O2<250 mTorr) and relatively high substrate temperatures (Ts≳800 °C). Since the linewidth of single‐crystal YIG is dominated by surface and volume defects and/or impurities, the narrow linewidth indicated that PLD is a viable technique for producing high‐quality ferrite films for microwave device applications. In addition, under all deposition conditions (50–1000 mTorr and 700–850 °C) there is a uniaxial axis perpendicular to the film plane. However, at low oxygen pressure ...

Design of a manufacturable discrete track recording medium

The potential benefits of patterning discrete tracks onto a disk for magnetic data storage have long been investigated. A practical process for manufacturing a cost-effective discrete track recording (DTR) medium has prevented such a disk from being introduced into a product. In this paper, a process utilizing nano-imprint lithography techniques to create a land and groove structure on the surface of a disk substrate will be described. Design considerations for the geometry of the structure, as well as of the magnetic write and read widths of the head, are discussed. Data showing the magnetic characteristics and recording performance of a DTR medium are also presented.

Oriented barium hexaferrite thin films prepared by pulsed laser deposition

Oriented thin films of barium hexaferrite, BaFe/sub 12/O/sub 19/, were grown in situ on (0001) sapphire substrates utilizing a pulsed laser deposition technique. X-ray diffraction, elastic backscattering spectrometry, ferrimagnetic resonance, and vibrating sample magnetometry confirm that the structure, composition, and magnetic parameters are consistent with films prepared by other techniques such as liquid phase epitaxy. >

Magnetic and structural characteristics of pulsed laser deposited epitaxial Y/sub 3/Fe/sub 5/O/sub 12/ films

Epitaxial Y,FqO, films were grown on (111) gadolinium gallium garnet substrates using the pulsed laser deposition technique. The results demonstrated that epitrusial YIG fiims could be prepared under a wide range of deposition conditions, but narrow linewidth (AH ii 1 Oe) films were produced only at low oxygen partial pressuresand relatively hih substrate temperatures. In addition, the fh exhibited a uniaxiial magnetic anisotropy parameter which changed sign from negative to positive with increasing oxygen partial pressure. I. INTRODUCXION Epitaxial Y

Ferrimagnetic resonance lineshape asymmetry due to Suhl instabilities

esO,z films were grown in order to determine if pulsed laser deposition (PLD) can produce high quality ferrite thin films. Yttrium iron garnet (YIG) is an ideal system to deposit for calibration purposes, since an abundant amount of information is available in the literature including data on liquid phase epitaxy (LPE) films and bulk single crystals. In addition, the linewidth, AH, of YIG is dominated by impurities and surface and/or volume defects. Thus, linewidth measurements can be used as a practical means to determine the quality of PLD YIG films and consequently the potential of the PLD technique for preparing high quality ferrite films in general. 11. EXPERIMENTAL

Novel technique for ferrimagnetic resonance measurements

We present calculations of the ferrimagnetic resonance lineshapes resulting from second order Suhl instabilities for thin films and spheres. We find that whereas a spherical sample has a lineshape which is symmetrical around the resonant frequency, a thin film has an asymmetrical lineshape. The calculations are in agreement with measurements that we have performed of the lineshape as a function of input power for thin film samples of both barium ferrite and yttrium iron garnet. When the magnetic field direction is changed from perpendicular to parallel to the film plane, the asymmetry of the lineshape at magnetic resonance changes in opposite sense relative to the resonant field. Theoretical estimates of the critical microwave field necessary for second order Suhl instabilities to occur are in agreement with measured critical fields.

YBCO microwave grain boundary mixer using a SrTiO/sub 3/ bicrystal substrate

The ferrimagnetic resonance (FMR) linewidth, Delta H, and resonant magnetic field of single-crystal (Mn-doped) Ba/sub 2/Zn/sub 2/Fe/sub 12/O/sub 22/ were measured as a function of frequency from 2 to 20 GHz. These measurements were performed utilizing a slot-coplanar device. The linewidth and resonant frequency measurements were found to compare well with those obtained using a standard FMR cavity technique, and the data were also in agreement with the behavior predicted by Landau-Lifshitz theory with the damping parameter alpha =0.0014. >

Planar superconducting YBCO microwave mixer employing an engineered grain boundary weak link junction

A microwave mixer was patterned on a microstrip transmission line of superconducting YBCO (YBa/sub 2/Cu/sub 3/O/sub 7-x/). The YBCO film was epitaxially laser deposited on a SrTiO/sub 3/ bicrystal substrate. A weak link was constructed by patterning a microbridge in the microstrip at the bicrystal boundary. Microwave signals at 9.000 GHz and 9.941 GHz were applied at the input of the microstrip line. An output intermediate frequency signal was observed at 941 MHz and was detected as the transmitted signal. The microbridge junction, which behaved as a resistively shunted Josephson junction (RSJ), was current biased slightly above the critical current I/sub c/. The mixer conversion loss was measured at the input and output ports of the device package. The mixing efficiency was determined at the device junction. This efficiency was compared with the calculated efficiency determined by numerical solution of the Josephson equation for the weak link junction. >

Structural and magnetic characterization of amorphous Gd2Fe14B thin films

A microstrip transmission line was patterned from a superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ film which was laser deposited on a SrTiO/sub 3/ bicrystal substrate. A microbridge in the microstrip was then patterned at the bicrystal interface to fabricate a superconducting grain boundary junction. Microwave mixing was observed with an input local oscillator frequency of 9.000 GHz, and an input signal frequency of 9.941 GHz. The output signal at 941 MHz was detected as a transmitted signal. The junction was current biased slightly above the critical current I/sub c/. The measured conversion loss was compared to the calculated value based upon a numerical solution of the equation for a superconducting weak link junction.<<ETX>>