Ulrich Ernst Enz

Permalloy/Sendust metal-in-gap head

By first depositing a thin films of Permalloy on a recording head no pseudogaps occur. At the gap the relative wear is slight, due to the presence of the Sendust. The gap cladding has minimal residual stress to avoid a decrease of head efficiency due to induced stress in the ferrite. The SiO/sub 2//Mo/Au gap is prepared by low-temperature thermodiffusion. This results in a magnetically sharp gap with a reproducible length. With this Permalloy/Sendust metal-in-gap head, a high-density recording head for in-contact recording has been realized. >

Light modified switching properties of garnets and ferrites

The influence of light on the switching behavior of Si-doped Y 3 Fe 5 O 12 and Co-substituted Ni-Zn ferrites is investigated. After irradiation with light, YIG (Si) has an extremely square hysteresis loop, and the switching transients display anomalous behavior. When a step field is applied, there is a certain period of time during which no flux is switched irreversibly. After this delay, which depends on the amplitude of the applied step field, the material switches in the normal way. At 4.2 and 77°K these changes are permanent; at 200°K the effects disappear after illumination is terminated. The results are discussed in terms of a two-center model, which was proposed earlier to explain results for changes in permeability. Co-substituted Ni-Zn ferrites show similar behavior already in the nonirradiated state. Irradiation increases the coercive force and also the break-free behavior becomes more pronounced. These changes are still permanent at 200°K.

Light‐Induced Increase in Domain‐Wall Stiffness in Si‐Doped YIG

The initial susceptibility of Si‐doped YIG is reduced by irradiation with light. This effect is explained by a simple two‐center model, a strongly anisotropic center being formed from a less anisotropic one by light‐induced electron transfer. Domain walls are pinned by these strongly anisotropic centers, of density n. If n is small enough, the stiffness will be proportional to n, since by local wall deformations each center within the wall can be made to occupy a site of lowest energy. For larger n this is no longer possible: instead, the optimum wall position will be determined by the statistical fluctuations of the center distribution, and the stiffness will be proportional to n1/2.

Fast wall motion in garnet films with orthorhombic anisotropy

High wall and bubble velocities have been observed in garnet films having a strong orthorhombic anisotropy. This anisotropy is induced by compressive misfit stress in garnets containing Mn3+ ions. The magnetostatics of bubbles in these orthorhombic materials differs from that in uniaxial materials, e.g., no hard bubbles have been observed for large in‐plane anisotropies. Under certain conditions automotion of bubbles has been observed indicating that vertical Bloch lines may be present. Wall mobilities of 55 m s−1Oe−1 and velocities up to 1400 m s−1 have been observed. The possibilities for small bubble diameter applications will be shown.

Static conversion of Bloch‐line number and the self‐collapse of hard bubbles

In bubbles carrying at least 100 Bloch lines, called superhard bubbles, the phenomenon of static conversion of the Bloch wall has been observed. Two experiments will be described in detail: (i) the dependence of the number of Bloch lines as a function of the temperature at which the material has been treated and (ii) the phenomenon of the self‐collapse of bubbles having Bloch lines in a supercompressed state.

Pulse induced suppression of flux switching in photomagnetic garnets

The observation of the suppression of flux switching induced by relatively long low-amplitude magnetic pulses is reported. This effect has been observed in Si-doped YIG in the irradiated state at low temperatures. Prior to the pulse-induced changes, the material is readily switched by pulses of amplitude H_{p} = 28.5 Oe and duration \tau_{p} = 5 mu s. After the application of conditioning pulses of amplitude, e.g., H_{cond} = 2 Oe and \tau_{cond} > 10 ms irreversible switching in the preceding large pulses H_{p}, \tau_{p} is suppressed. These observations are discussed in terms of the displacement of domain walls pinned by centers (Fe2+ions) having a wide range of pinning strength and relaxation times.