The Initial Susceptibility of Cobalt after Electron Irradiation at 4.2 K

Abstract

After electron irradiation at 4.2 K the initial ferromagnetic susceptibility of cobalt shows a marked decrease ("susceptibility dip") of about 50% when the specimen is annealed between 20 and 30 K and rega,ins its initial value in recovery stage I, of the electrical resistivity between 40 and 50 K. Similar, yet smaller "susceptibility dips" are observed at 5,55,70, and 150 K . The 30 K decrease of the initial susceptibility is t,entatively ascribed t o the pinning of domain walls by interstitial atoms of hexagonal symmetry in the [0001]-dumbbell configuration which, however, may be stable only under the influence of close Frenkel pairs in their neighbourhood. This model is in good agreement with simultaneous electrical resistivity and magnetic after-effect measurements reported elsewhere which indicate that the anisotropy axis of the freely migrating interstitial atom has a component parallel to the basal plane. Nach Elektronenbestrahlung bei 4,2 K zeigt die Anfangssuszeptibilitat von Kobalt eine starke Abnahme (,,Suszeptibilitltsloch") urn ungefahr 50%, wenn die Probe auf Temperaturen zwischen 20 und 30 K angelassen wird; sie erreicht wieder ihren Ausgangswert im Temperaturbereich zwischen 40 und 50 K, in dem auch eine starke Erholung des elektrischen Widerstandes (StufeI,) stattfindet. Ahnliche, jedoch kleinere ,,Suszeptibilitatslocher" werden bei 5, 55, 70 und 150 K beobachtet. Die bei 30 K beobachtete Abnahme der Anfangssuszeptibilitat wird vorlaufig durch Pinning-Prozesse zwischen Blochwiinden und Zwischengitteratomen hexagonaler Symmetrie in der [0001]-Hantelkonfiguration erklart ; diese Konfiguration scheint jedoch nur bei Anwesenheit eines nahen Frenkelpaares stabil zu sein. Dieses Model1 ist in guter Ubereinstimmung mit gleichzeitig durchgefiihrten Messungen des elektrischen Widerstandes und der magnetischen Nachwirkung, die an anderer Stelle veroffentlicht werden und die darauf hinweisen, daB die Anisotropieachse des frei wandernden Zwischengitteratoms eine Komponente parallel zur Basisebene besitzt.

Magnetic Aftereffect Phenomena in Cobalt between 4.2 and 20 K after Low‐Temperature Electron Irradiation

“…9. As shown in a previous paper [5] the decrease of the initial susceptibility around 20 K and its increase around 50 K is due to annealing processes.…”

“…I n this case the jump frequency depends on the position of the defect in the wall and is given by [15] v = v e(Esin'p)lkTe-QILT , where E sin2 p corresponds to the magnetic interaction energy of a defect of hexagonal symmetry and rp to the angle between the spontaneous magnetization and the c-axis. Since elkT may be of the order of magnitude of +(lo to 20) [ 5 ] we have to expect a broad spectrum of jump frequencies. For the calculation of the time dependence of the relaxation process these jump frequencies have to be weighted in a rather complicated manner, depending on the spin arrangement within the domain wall.…”

Electrical resistivity recovery of cobalt after low‐temperature electron irradiation

“…1 the damage rate of cobalt irradiated at 4.2 K by electrons decreases slowly for doses between 1OI8 and 8. 6 x 10l8 e-/cm2. The damage rates differ slightly from specimen to specimen and may depend on the purity of the specimens.…”

“…In our experiments, electrical resistivity, initial susceptibility [6], and magnetic aftereffect studies "7, 81 after low-temperature e--irradiation have been performed simultaneously in the same experiment and on the same specimen in order to enable direct correlations between the three measuring quantities.…”