J. C. Suits

Thermomagnetic writing in Tb‐Fe: Modeling and comparison with experiment

Computer model calculations and experimental comparison are presented for thermomagnetic writing in TbFe media. Two models are discussed which are appropriate for two observed types of writing behavior. A ‘‘bubble’’ type writing model is found to give good experimental agreement when wall motion processes dominate and the laser‐written marks exhibit single‐domain behavior. This model accurately accounts for the writing behavior of Tb0.23Fe0.77. The gradient of the domain‐wall energy is found to be an important factor in the writing process and can cause nucleation to be delayed until some cooling has occurred. This results in written domain sizes which are a strong function of the applied bias field. For compositions which exhibit multiple domain writing behavior, a ‘‘nucleation field’’ model is found to be appropriate. This model predicts the observed weak dependence of mark size on applied bias field. In addition, the nucleation field model is used to calculate the bias fields which correspond to the on...

Faraday and kerr effects in magnetic compounds

Some recent work on the magnetooptical properties of magnetic insulators and semiconductors is reviewed. Emphasis is placed on understanding the atomic origin of the Faraday and Kerr effects in terms of molecular-orbital energy levels. The classes of materials discussed are chromium trihalides, orthoferrites, garnets, ferrites, chromium spinels, and divalent europium compounds.

Preparation and properties of EuO films

Films of EuO have been vacuum deposited by three techniques: electron beam heating of bulk EuO, simultaneous deposition of Eu and Eu 2 O 3 , and evaporation of Eu in a partial pressure of oxygen. X-ray measurements show the structure of these films to be essentially the same as bulk EuO. The Faraday rotation of EuO films was measured at 5° K for wavelengths between 0.5μ and 1.2μ. The largest specific Faraday rotation occurs at a wavelength of 0.66μ and is 5 × 105degrees per cm, which is one of the highest values yet reported for any material. From magneto-optical measurements and force balance measurements, various magnetic properties of these films have been determined and compared with bulk EuO. Magnetic moment, susceptibility, and squareness of EuO films do not differ greatly from bulk. The coercive force, however, is several times bulk value, and appears to be related to stress in the films.

Structural instability in new magnetic heusler compounds

Abstract The crystal structure and magnetic properties have been determined for a new series of compounds of the form Rh2TSn. For T = Mn, Ni, or Cu, the room temperature structure is the fully ordered cubic Heusler structure. For T = V, Cr, Fe, or Co, a new structure is observed which is an exceptionally large tetragonal distortion of the Heusler structure (c/a = 1.18−1.27). The appearance of this tetragonal distortion is attributed to an electronic instability of the band Jahn-Teller type.

Lorentz microscopy of micron‐sized laser‐written magnetic domains in TbFe

High resolution images of laser‐written magnetic domains in thin sputtered films of terbium iron have been obtained using Lorentz microscopy. The domains, written with a GaAs diode laser, are generally circular in shape with diameters in the range 0.9–2.2 μm. Conditions necessary for the observation of highly detailed images are described. It was found that with certain values of laser power and applied magnetic field, smaller irregular domains appear within the principal domains.

Thermomagnetic direct overwrite in TbFe using thermally induced domain wall energy gradient

A method is described for thermomagnetic direct overwrite in amorphous Tb23 Fe77 . Using long (500 ns) laser pulses, micron‐size domains can be written with diameters significantly smaller than the diameter of the Curie temperature isotherm. The relatively small domain size is due to the collapsing effect of the thermally generated domain wall energy gradient. Without switching the magnetic bias field, the domains can be collapsed to submicron size using short (50 ns) laser pulses. Domains can be completely erased by firing short pulses in succession as the recording medium is moved slowly with respect to the optical beam.

Magnetic, corrosion, and surface properties of Ni‐Fe‐Cr thin films

Films in the Ni‐Fe‐Cr ternary system were evaporated and examined with regard to magnetic properties, resistance to atmospheric corrosion, and surface chemistry. It was found that films with relatively high magnetization and low coercive force could be made which at the same time exhibited good corrosion resistance. The corrosion occurred predominately by pitting for the low chromium concentration films. The surface chemistry was studied by Auger and XPS techniques which indicated that addition of Cr to Ni‐Fe caused replacement of a nonpassivating iron‐rich oxide surface layer by a passivating Cr‐rich oxide layer.

Observation of laser‐written magnetic domains in amorphous TbFe films by Lorentz microscopy (invited)

A review is given of Lorentz microscopy and its application to the study of laser‐written domains in amorphous rare‐earth/transition‐metal–type materials. Domains, or regions of reverse magnetization, were written under various conditions of laser power and applied magnetic field in TbxFe1−x films where x varies in the range 0.14–0.32. Upon examination by Lorentz microscopy, and under certain conditions, these written regions show highly detailed magnetic structures. One condition for obtaining good images is the avoidance of oxidized surface layers showing in‐plane magnetization. Another condition is tilting of the film plane in the transmission electron microscope to enhance image contrast. A variety of domain structures have been observed ranging from fully saturated regions with both highly regular and irregular boundaries, to fully demagnetized regions. An example of correlation between the field dependence of the microstructure and measurements of magneto‐optical signal is given for the x=0.32 compo...

Refractive index of garnet films containing Ca and Ge

Refractive‐index–vs–wavelength data are reported over a wavelength range of 0.56 to 0.97 μ for several garnets containing Ca2+ and Ge4+ and various compositions of rare‐earth ions. The experimental data were fitted to a two‐term Sellmeier expression and a linear relation between index of refraction and number of Fe3+ ions was found for garnet composition with small rare‐earth content.

REFLECTIVITY AND BAND STRUCTURE OF EuO

Near‐normal incidence reflectivity of single‐crystal EuO is reported for the energy range 1–9 eV. Results are interpreted in terms of recent band‐structure calculations.