Untersuchung der Neutronendepolarisation von Dy in der Umgebung von magnetischen Umwandlungspunkten

It is possible to determine the dimensions of the ferromagnetic correlation range by depolarisation measurements of polarized thermal neutrons near magnetic transition points, where small magnetic domains (< 10^?4 cm) are present. The dimensions of the magnetic domains of Dy were determined in the temperature range from 4,2 °K to room temperature and in an external magnetic field from 0 to 2,4 kOe. The size of the domains increases with decreasing temperature and increasing external field. For low temperatures a sort of internal coercive force for the wall mobility was observed, which strongly hinders the formation of greater ferromagnetic domains. At the Curie-point the ferromagnetic correlation range shows a continuous transition and goes only slowly to zero when the temperature increases.     

Zum Magnetismus von aufgedampften Silber-Mangan-Legierungen

Ag-Mn alloys are produced by simultaneous condensation of both components on a substrate at 30 °K. By this method one gets a statistic distribution of the Mn atoms in Ag. The susceptibility of unannealed films obeys Curie's law for all Mn concentrations up to 16 at. per cent. Above that concentration the Curie-Weiss law holds with a negative paramagnetic Curie temperature. The magnetic moment decreases with increasing Mn concentration. For small concentrations the magnetic moment of a Mn atom corresponds to a spin of 4/2. The temperature of spin ordering is proportional to the Mn concentration. Annealing the films to 300 °K changes the distribution of the Mn atoms and the magnetic properties. The magnetic measurements on annealed films qualitatively agree with known measurements on molten Ag-Mn alloys. The magnetic properties are discussed by using theoretical arguments given byFriedel, Ziman, andOverhauser.     

Ferromagnetismus von amorphem Eisen

In a previous paper a method has been described to produce thin films of amorphous iron by simultaneous condensation of iron and small additions of oxygen, silicon, or germanium onto a substrate at 20 °K. During annealing the amorphous films crystallize within a narrow range of temperature. In this paper the magnetic properties of these films are investigated. By a new lowtemperature ?gnetometer the magnetization curves can be registered for the different states of annealing. It results that even in the amorphous state iron is ferromagnetic. Below a critical concentration of the oxygen, silicon, or germanium admixtures the magnetic moment of the iron atoms is smaller and the coercive force is greater in the amorphous than in the crystalline structure. Above that concentration the magnetic moments in the two structures are equal, whereas the coercive force of the amorphous films is smaller than that of the crystalline ones. The results are explained by a concentration depending short range order in the amorphous films.     

Magnetische und kalorische Eigenschaften von Alkali-Hyperoxid-Kristallen

The phase transitions of Alkali-Hyperoxide crystals (NaO₂, KO₂, RbO₂, and CsO₂) grown in liquid ammonia have been investigated by means of the following measurements:

1. magnetic susceptibility
2. differential magnetic susceptibility as magnetic field
3. magnetization curve in static and pulsed fields
4. specific heat.

The anomalies of the specific heat could be correlated with the magnetic properties and structural changes. Several new phase transitions were found. The magnetic behaviour of NaO₂ indicates magnetic order (of as yet unknown nature) at low temperatures. The magnetic and caloric behaviour of KO₂ at low temperatures is compatible with a Néel point at 7 K. A metamagnetic transition can be induced at temperatures below 12 K with fields of about 70 kOe. This transition is connected with structural changes. RbsO₂ and CO₂ are probably antiferromagnetic with Néel temperatures of 15 K and 9.6 K, respectively.     

Supraleitung von Pb- und Sn-Schichten nach Implantation von Mn-Ionen

Ion-implantation is a useful method when preparing dilute alloys, especially of elements with very low solubility like 3d-transition-elements in most non-transition superconductors. A strong decrease inT _c and an increase in the residual resistivity were observed in Pb- and Sn-films doped with Mn-ions. Nonlinearity in theT _c -dependence which was found at very low concentrations (0-100 ppm) is caused by lattice defects. They cannot be avoided if implantation method is used. This was proved by irradiation with nonmagnetic ions of comparable mass (such as Cu or Zn). The linear part in theT _c -depression is compared with results obtained with the quenched film technique by Barth (Pb-Mn) and Schertel (Sn-Mn). A discrepancy to these measurements is found in the case of Sn-Mn. The increase in film resistivity is due to lattice defects as well as magnetic impurities. The magnetic contribution (p/c) _m =(4.5 ± 0.2) μΩ cm/at-% agrees well with a theoretical calculation. Heavily doped Sn-films show a small Kondo-resistance-minimum at 7 K with a depth of 2.5‰ of the residual resistivity.     

Neutronenbeugungsuntersuchungen der magnetischen Struktur von TmCo3

The magnetic structure of the intermetallic TmCo₃ compound, determined by neutron diffraction measurements at 4.2 K on a powder sample, is colinear to the hexagonal c-axis, with the magnetic moments of Tm- and Co-ions being antiparallel coupled. The saturation moments have been found to beµ(Tm)=6.5µ _B andµ(Co)=0.8µ _B . The calculated magnetic moment of the Tm-ion by crystal field theory, based on a point charge model, is that of the free Tm³⁺ ion.     

Magnetische Eigenschaften von wasserfreiem Cer- und Praseodymchlorid

The magnetic susceptibility of single crystals of anhydrous cerium and praseodymium chloride has been measured for the two principal crystal axes in the temperature range from 4·4°K to 300°K. From the magnetic susceptibility the linear and quadratic Zeeman-effects of the two lowest crystal field components of ths electronic ground states are derived. The results are in good agreement with comparable measurements reported by other authors.     

Spinpolarisation von Feldemissionselektronen aus einkristallinem Wolfram

Field-emitted electrons from tungsten tips extracted in magnetic fields of 3–25 kG at 80 K show spin polarization. The observed polarization is always found to be parallel to the external magnetic field for the polycrystalline and oriented tips (〈100〉, 〈110〉 and 〈111〉) investigated. The maximum values of polarization obtained with these monocrystalline emitters range betweenP _max=11–13 percent.     

Neutronenbeugungsuntersuchungen der magnetischen Struktur von TmCo3

The magnetic structure of the intermetallic TmCo₃ compound, determined by neutron diffraction measurements at 4.2 K on a powder sample, is colinear to the hexagonal c-axis, with the magnetic moments of Tm- and Co-ions being antiparallel coupled. The saturation moments have been found to beµ(Tm)=6.5µ _B andµ(Co)=0.8µ _B . The calculated magnetic moment of the Tm-ion by crystal field theory, based on a point charge model, is that of the free Tm³⁺ ion.     

Zur Abbildung von Magnetisierungsstrukturen mit dem Faraday- und Kerr-Effekt

Ferromagnetic domains were observed by means of the Faraday- and Kerr-effect using the bright field as well as the one-sided, real symmetric and rigorous dark field method. By these experiments it is demonstrated that the light which is diffracted by magnetic domains is polarized perpendicular to the incident wave and that magnetic structures can be observed without any polarizer or analyzer. Applications of these diffraction phenomena and the consequences for the resolving power of magnetooptic microscopy are discussed. Magnetooptic pictures must be interpreted carefully to avoid erroneous results, especially concerning the observation of domain walls.     

Subharmonische Resonanzen und Oberwellenmodulationseffekte in einem Gemenge von optisch gepumpten Atomkernen unter dem Einfluß von linear-polarisierten magnetischen Wechselfeldern

The dynamical equation is solved for an optically pumped spin system under the influence of a static and alternating circulary or linearly polarized magnetic field by a recursive numerical method. The results are graphically represented for a special set of parameters.     

Ein Demonstrationsversuch zur Hyperfeinaufspaltung von Atomen

An Experiment to Demonstrate the Hyperfine Splitting of Atoms in a Lecture Hall The detection of laser induced fluorescence from a thermal atomic beam allows in a simple way for the observation of the hyperfine splitting of ground and excited Na-atoms. A suitable experimental setup is able to show in a lecture hall not only the atomic beam itself but also the consequences of electron and nuclear spin. The laser light used is transmitted from the laser in the laboratory into the lecture hall by a fiber glass cable. The experiment is able to show also the effects of optical pumping and, if additionally an external magnetic field is applied to the observation region, the Zeeman effect.     

Ferromagnetische Resonanz von polykristallinem Nickel in Abhängigkeit von Temperatur und Frequenz

Resonant magnetic field and linewidth of bulk nickel were determined between ?160 °C and room temperature at the frequencies of 9.2, 19.7 and 26.2 Gc/s. At 19.7 and 26.2 Gc/s the resonance-field shift is found to be proportional to the anisotropy field. Below ?90 °C the linewidth can be described by the independent-grain theory. For temperatures above ?90 °C the validity of the dipole-narrowing model is discussed. At 9.2 Gc/s resonance field and linewidth are strongly influenced by additional absorption peaks caused by domain structure.     

Frei zerfallende Magnetfelder von Kugelschalen

The decay constants of free decaying magnetic fields of sphere shells are calculated. In the regionr ₁<r<r ₀ the electrical conductivity isσ. For different values of the parameterγ=r ₀/(r ₀-r ₁) the following models are considered: The conductivity is zero forr>r ₀ andr<r ₁ (model 1). The conductivity is zero forr>r ₀, and forr<r ₁ the magnetic field is excluded by infinite conductivity (model 2). The magnetic field is excluded forr>r ₀ andr<r ₁ (model 3).     

Magnetische grenzflächen-anisotropie von amorphem Fe in kontakt mit nichtmagnetischen metallen

The magnetic properties of very thin ferromagnetic Fe films (1–10 atomic layers) in contact with nonmagnetic amorphous metals are investigated. Apart from the demagnetization energy, which supports a magnetization in the plane of the film, an energy of magnetic anisotropy occurs in the interlayer, which has the tendency to orient the magnetization perpendicular to the surface. The anomalous Hall effect of the ferromagnetic films is used to investigate their magnetic properties. From the measurements, we get the applied magnetic field B_s, which is necessary to orient the magnetization perpendicular to the film surface. In addition to a constant term, B_s is proportional to 1/d, which is typical of surface effects and yields the energy of the interface anisotropy. The value of this energy is strongly dependent on the nonmagnetic metal and is smaller for the system Pb/Fe than for Sn/Fe. Furthermore, the experimental results show no drastic reduction of the atomic magnetic moment in the surface layer.     

Elektronische Eigenschaften vonγ-Messing

The intermetallic phase of the alloy system Cu-Zn, defined in the region of 58–69 at% zinc, is calledγ-brass. We have measured the electric conductivity, the Seebeck coefficient, the Hall constant, the magnetoresistance in high fields and the magnetic susceptibility of this alloy as a function of composition and temperature. We have found an oscillatory behaviour of the transport coefficients as a function of composition. The Seebeck coefficient shows oscillations around zero. The three zeros coincide with the maxima and minima (between 62 and 67 at% zinc) of the other transport coefficients. The magnetic susceptibility increases rapidly with increasing zinc concentration up to the maximum of ?53·10^?6 (cgs/grammatom) at 67 at% zinc. For the discussion of the results the band scheme of the empty lattice and the model ofJones have been extended.     

Elektronendichteverlauf in magnetisierten Wasserstoffbögen bei Abweichung der Ionentemperatur von der Elektronentemperatur

We investigate theoretically the magnetic properties of a realistic layer type ferromagnet which differs from an isotropic two-dimensional Heisenberg magnet due to small anisotropy and interlayer coupling. An approximation is used which contains the vanishing of long range order and the existence of a Stanley-Kaplan phase transition in the ideal limit. The approach of the ideal limit is studied. Detailed results are presented both in the neighbourhood of the magnetic phase transition and in the low temperature region. The closeness to the isotropic two-dimensional limit has a strong influence on the behaviour in finite magnetic fields for realistic values of anisotropy and interlayer coupling. However, exceedingly small values of these parameters are required to affect the spontaneous magnetization.     

Messungen von Äquivalentbreiten im Homogenen Magnetfeld

The equivalent width of spectral lines with fine and hyperfine structure is not always increased by an external magnetic field, but can be reduced drastically. This prediction from theory has been checked by magnetooptical measurements for the Na-D₁-line and has been found to be correct in all essential details. Furthermore the experimental results demonstrate, that the formulae normally used to calculate the saturated vapour pressure of metals are valid only for a limited number of cases. Moreover the experiments furnish the basis for a more exact method for determinating particle densities in metal vapours.     

Kollektiver Magnetismus von Ho2O3 im Temperaturbereich von 1,1 bis 4,2°K

A mutual inductance bridge (Hartshorn bridge) was used to measure the magnetic susceptibility of single crystals and powder samples of Ho₂O₃ in the temperature range between 1,1 and 4,2°K and in external field up to 3,5 kOe. At approximately 1,2°K Ho₂O₃ undergoes a magnetic transition. A magnetization relaxation and hysteresis effects are found near the transition temperature.     

Das kritische Magnetfeld von dünnen supraleitenden Doppelschichten

Thin superposed films of two superconductors or of a superconductor and a normal metal in a surface parallel magnetic field are considered, assuming that the mean free path of electrons is very short (dirty limit) and that the films are very thin (Cooper limit). From the linearized integral equation for the order parameter and the diffusion equation for the kernel with appropriate boundary conditions at the surfaces and at the interface, an equation for the critical magnetic field is derived. For small magnetic fields and for superposed films consisting of metals which are not too different in their physical properties, our results are in agreement with those obtained earlier byKlein andFischer. For high magnetic fields, however, there are essential differences.