Die Temperaturabhängigkeit der Koerzitivkraft von Mangan-Ferriten

Ohne Zusammenfassung

---

     

Die Temperaturabhängigkeit des Funkelrauschens Bei feldemission

The noise of the emission current as a consequence of the flicker effect was investigated in ultra-high vacuum. The measurements were made in an autoemission electron microscope constructed after E. W. Müller. The paper gives some of the results concerning the temperature dependence of the spectral distribution and of the mean square value of the fluctuation current from tungsten cathodes at the adsorption of residual gases and barium.The results of the measurements are compared with the results derived on the basis of a theoretical model which is described in greater detail in another paper. The interpretation of the observed activation energies of noise is discussed by means of surface migration.

---

---

Herin Dipl.-Phys. H. Sobotta danke ich ftir die Überlassung experimenteller Ergebnisse und Diskussionen.     

Die Temperaturabhängigkeit des magnetischen Barkhausen-Effekts. I

The apparatus described allows to measure the size distribution of Barkhausen discontinuities with a magnetic moment greater than 10^?6 e.m.u. in a temperatur range from liquid air up to the Curie point. We used the counting method, developed byTebble and his co-workers, in connection with a multichannel-analyzer. Nickel samples of different purity and of different thermal treatment have been investigated. The results are as follows: 1. The size distribution of two samples, having in practice the same hysteresis loop can show a completely different behaviour as a function of the magnetic field. 2. The number of great discontinuities is reduced more rapid with rising temperature than that of the smaller ones; thus leading to the conclusion, that the Barkhausen component of total magnetization is vanishing much stronger with increasing temperature than that of differential susceptibility. 3. The critical field strength, being characterized by a maximum in the number of discontinuities per unit field, shows the same temperature dependence as the coercive force. This critical field is only slightly dependent on the size of jumps. 4. The “average” magnetic moment of the discontinuities in the measured range of size appears to vary less with temperature than the spontaneous magnetization. 5. Above a temperature of about 270°C spontaneous jumps will be produced, even in a magnetic hard sample, by diminutive vibrations, such as speaking loud or coughing. 6. The Barkhausen part of total magnetization varies with temperature like the coercive force and therefore seems to be a structure-dependent quantity. The results of our measurements are discussed in connection with those of other authors.     

Die Temperaturabhängigkeit des magnetischen Barkhausen-Effekts. II

The size distribution of Barkhausen discontinuities was measured during “thermal idealisation” of a hard drawn nickel specimen. Thermal idealisation means the magnetization by increasing temperature in a constant magnetic field. The sensitivity of the apparatus covered a range of magnetic moment between 1.3 and 17.3·10^?6 e.m.u. The results are in good agreement with investigations ofGerlach andTemesváry on the irreversible part of thermal idealisation. The average volume of Barkhausen discontinuities of the measured size was found to be nearly independent of temperature in a range from ?150 to+200°C, while above 200°C the volume increases markedly with temperature. By means of the average Barkhausen volume the temperature dependence ofNéels thermal fluctuation field was calculated. The results are in good agreement with those ofPescetti andBarbier on the temperature dependence of magnetic after effect.     

Temperaturabhängigkeit der Knight-shift von Molybdän

Measurements of the magnitude, sign and temperature dependence of the Knight-shiftK and magnetic susceptibility in Molybdenum metal were carried out. Detailed analysis of these data shows that the principal contribution toK and arises from the orbital part. The temperature dependence ofK and is due mainly to the orbital part and not to the core polarization part as it is known for other transition metals. Theoretical calculations are in agreement with these results.The experiments were carried out in a magnetic field of 80 kG and over the temperature range 300T1200 K.     

Die Bestimmung des Frequenzfaktors und der Haftstellentiefe aus der Temperaturabhängigkeit der Elektrolumineszenz von ZnS-Phosphoren

The temperature dependence of the a.c. electroluminescence of ZnS-phosphors shows characteristic features which are closely related to the energetic distribution of traps. Measurements over a wide range of exciting field frequencies are used to determine frequency factors and trap depths with high accuracy. The order of magnitude of the obtained frequency factors agrees with theoretical values and results of other authors, who investigated CdS single crystals by different methods. The trap depths resulting from electroluminescence measurements are lower than those estimated from glow curves. This deviation can be explained by considering multiple retrapping and a low quantum efficiency of the thermoluminescence. An expression for the trap depth in dependence of the temperature of a glow maximum is derived, which is valid for all kinetics of thermoluminescence.     

Die Temperaturabhängigkeit der Photoluminiszenz der silberaktivierten Zink-Kadmium-Sulfide

Zusammenfassung Bei der thermischen Tilgung der Lumineszenz von Sulfiden, die durch Silber aktiviert sind und Kupfer oder gegebenenfalls auch Nickel enthalten, kommt neben dem üblichen umkehrbaren Prozess ein zweiter Prozess mit hystereseförmigem Verlauf zur Geltung; ausserdem wurden Prozesse mit einer komplizierteren Abhängigkeit beobachtet, die u. a. mit der photolytischen Schwärzung zusammenhängen. Die Temperaturabhängigkeit der langwelligen Lumineszenz unterscheidet sich bei einigen Proben von der Abhängigkeit des Maximums der Spektralkurve. Es wurde ein nichtumkehrbares Anwachsen der langwelligen Lumineszenz bei der Erhitzung beobachtet. Angedeutet wird der Zusammenhang der beobachteten Erscheinungen mit der chemischen Zusammensetzung der Leuchtstoffe.Diese Arbeit, die einen Teil der Aspirantur-Dissertationsarbeit darstellt, wurde auszugsweise auf der I. Tagung der tschechosl. Physiker in Prag am 27. 9. 1957 vorgetragen.