摘要:

To measure the surface impedance of metals from 2 to 0.2 mm wavelength, we have utilized a lamellar interferometer and a bolometer detector which operates at 0.4°K. A simple transmission‐line sample geometry is used to make the metal samples compatible with our Fourier‐transform spectroscopic technique. The applicability of this method to magnetic resonance studies has been demonstrated by the observation of ferromagnetic resonance in nickel in large magnetic fields. An investigation of ferromagnetic Dy and Tb metals has proved somewhat more interesting because in both metals the magnetoelastic interaction energy is extremely large. From the temperature dependence of the ferromagnetic resonance in zero field we have found that the lattice does not follow the precessing magnetization during resonance.

ISSN:0021-8979    

DOI:10.1063/1.1659048

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The effects of exchange on the magnetostatic surface and bulk spin waves of a ferromagnetic film in the regime where the dipole and exchange fields are both important are determined from the solutions of a sixth‐order differential equation. The eigenstates are admixtures of bulk and surface waves. With an applied magnetic field parallel to the film surface and for small values of the wave vector parallel to the surface,k, the Damon and Eshbach surface state is split into segments which join adjacent bulk branches. No sharp cutoff of the surface branch occurs as the angle betweenkand the applied field is increased, instead the character of the branch changes continuously from surface‐like to bulk‐like. For values of| k |≳104a number of branches have significant surface character so that no single branch can be identified with the Damon‐Eshbach surface state. When the applied field is perpendicular to the surface a new type of surface spin wave occurs below the bulk manifold and is characterized by a complex wave vector normal to the surface. These surface states exist only when the dipole and exchange energies are comparable. By including microscopic perturbations in the boundary conditions it is shown that these states map smoothly into the microscopic solutions for the Heisenberg model. Detailed calculations of the dispersion curves of the bulk and surface spin‐wave frequencies and eigenvectors are presented for yttrium iron garnet for both the parallel‐ and perpendicular‐field cases.

ISSN:0021-8979    

DOI:10.1063/1.1659049

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Measurements of room temperature susceptibility in the basal plane of natural single crystals of &agr;‐Fe2O3in which a high field isothermal remanence has been induced reveal a substantial anisotropy whose minimum is coincident with the direction of remanence. The susceptibility anisotropy appears to be related primarily to the low coercivity fraction of the remanent moment. Sizeable discontinuous changes in the susceptibility are sometimes present as the specimen is rotated. Recent domain wall studies have disclosed the presence in synthetic crystals of 180° walls exclusively. The present work suggests that the magnetization process within the basal plane of natural crystals of hematite is more complex.

ISSN:0021-8979    

DOI:10.1063/1.1659050

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

We have used a high‐resolution spherical Fabry‐Perot interferometer and a single‐frequency laser to measure the time dependence of local fluctuations of order in the isotropic phase of a nematic liquid crystal. We find a critical slowing of the fluctuations analogous to the critical slowing of spin fluctuations in a ferromagnet. The fluctuations relax exponentially with a single relaxation time &tgr;. Over two decades of &tgr; we find that &tgr;∼ (T−Tc)−&ggr;with&ggr;≃43andTcslightly below the temperature at which the first‐order transition to the nematic phase occurs.

ISSN:0021-8979    

DOI:10.1063/1.1659051

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The voltage‐magnetic field phase diagram is explored for a nematic liquid crystal aligned between rubbed conductive glass plates. New patterns of long‐range order are found for ac excitation and nonzero magnetic field. The variation of conductance with changes of order and with the angle with respect to the nematic director have been measured. An unexpected onset of turbidity is found at a voltage proportional to applied field when current is flowing parallel to the director.

ISSN:0021-8979    

DOI:10.1063/1.1659052

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

To study the relationship between biological function and the electronic state of the central Fe atom of hemoproteins, magnetic susceptibilities have been measured down to pumped liquid‐helium temperature. It was found that the magnetic susceptibility of ferric and ferrous hemoglobin is sensitive to the sample preparation. From EPR measurements of hemoglobin, it was concluded that this fluctuation of the magnetic susceptibility is due to a high‐spin to low‐spin transition induced by a conformational change of the protein molecule. For ferrous hemoglobin (pH = 7), it was found that fine structure of the lowest ground‐state energy level is described by the spin HamiltonianD Sz2(D= 4 cm−1). The field dependence of magnetization of this compound was measured up to 50 kOe at 4.2°K in a superconducting magnet. By determining the deviation from the linear relationship between magnetization and magnetic‐field strength, splitting of the lowest ground‐state energy level was shown to be represented by the same value ofD.

ISSN:0021-8979    

DOI:10.1063/1.1658784

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The function of ferritin is to stock the iron present in the body. Ferritin consists of a protein shell surrounding a core which is mainly an iron hydroxide FeOOH. Mo¨ssbauer effect and magnetic measurements in the temperature range 2°–300°K show ferritin to be superantiferromagnetic with grains 70 Å in diameter. This condition is characterized by a blocking temperature and a thermoremanent magnetization. The magnetic moment of each grain is about 1.2 × 10−18emu and the surface anisotropy is 5.8 × 10−2erg/cm2. In aqueous solution, ferritin retains its magnetic properties apart from a slight modification due to the penetration of water which expands the grains. Ferritin can contain up to a maximum of 23 wt% iron without any profound effect on the basic magnetic properties. High pulse field experiments (175 kOe) show ferritin to behave as a metamagnet with a threshold field of 75 kOe. The core of the molecule has hexagonal crystal structure witha= 11.79 Å andc= 9.90 Å, resembling the planar compact structure of oxygen in &dgr;‐FeOOH. The iron atoms are situated on the tetrahedral and octahedral sites of the lattice. Some of this work has been published elsewhere: A. Blaise, J. Chappert, and J. L. Girardet, Compt. Rend. 261, 2310 (1965); A. Blaise, J. Feron, J. L. Girardet, and J. J. Lawrence, Compt. Rend. 265, 1077 (1967); J. L. Girardet and J. J. Lawrence, Bull. Soc. Franc. Mineral. Crist. 91, 440 (1968).

ISSN:0021-8979    

DOI:10.1063/1.1658785

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

59Co NMR measurements in a series of alloys consisting of 0.3 to 1.2 at.% Co dissolved in TixMo1−xand NbxMo1−xhosts, where 0≤x≤0.4, have been used to demonstrate that the continuous decrease in theaveragemoment on the Co impurities with increasing Ti (Nb) concentration in the host does not result from a continuous decrease in the moment value of each Co ion but rather is due to an increasing number of Co ions which discontinuously become nonmagnetic. These results provide the first direct evidence for the applicability of the Jaccarino‐Walker concept of discontinuous moment formation depending upon the local environment of the impurity. They clearly demonstrate that the qualitative explanation for the systematic variation in the average moment on iron group impurities dissolved in the 4dtransition series based on theU/&Dgr; condition of the Anderson model and the average density of states of the host is inadequate for these alloys.

ISSN:0021-8979    

DOI:10.1063/1.1658786

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

Magnetic ordering and superconductivity have been investigated in the system Sn0.97‐xMnxTe for 0.00001≤x≤0.16 over the temperature range 0.02≤T≤300°K. Reciprocal Hall coefficient, 1/Re, for all these samples was ∼1021cm−3. Samples withx>0.005 showed ferromagnetic ordering with the Curie temperatures varying linearly withx. For 0.0001<x<0.005, neither magnetic ordering nor superconductivity were observed above 0.02°K. In samples withx<0.0001 superconductivity has been observed with the transition temperatures being depressed below that for Sn0.97Te (Tc≃0.20°K). Measurements have also been made on samples with constant manganese concentration and varying carrier density. Heat capacity measurements between 2°–30°K showed anomalies attributable to the magnetic coupling of the Mn ions. These results will be discussed in terms of current long‐range indirect‐exchange interaction theories.

ISSN:0021-8979    

DOI:10.1063/1.1658787

出版商:AIP    

年代:1970

数据来源: AIP

摘要:

The electrical resistivities of several Pd alloys with Np concentrations ranging from dilute amounts up to 13 at.% have been measured from 1.6°–300°K. For Np compositions below 7.5% resistivity minima were observed. Magnetic susceptibility data on the alloys containing 2.5%–13% Np indicate localized moments at high temperatures and spin compensation at low temperatures. The Kondo temperature of the dilute alloys is estimated to be of the order 10°–100°K.

ISSN:0021-8979    

DOI:10.1063/1.1658788

出版商:AIP    

年代:1970

数据来源: AIP