摘要:

In some Rare Earth‐Transition Metals compounds the anisotropy shows a complex behaviour: easy direction of magnetization out of the crystallographic axis, large high order anisotropy constants and jumps in the magnetization curves were measured. We observed that these effects were present in systems where the anisotropies of the various sublattices were strong and opposite (axial vs. planar) and where the exchange was not strong enough to completely dominate. We developed a quantitative model taking into account the competition between the exchange and the difference in the anisotropies allowing for possible canting between the sublattice magnetizations. We found that a canting angle is indeed possible although it is small and dependent on the orientation of the resultant magnetization. However the possibility of deviating from the collinear order results in an energy relaxation that greatly distorts the shape of the anisotropy energy surface. Consequently the anisotropy of the resulting system cannot be described by the sum of the anisotropy constants of the individual sublattices: strong corrections and higher order terms must be taken into consideration. These corrections, calculated from realistic values of the parameters, turn out to have the right sign and magnitude so as to justify the observed phenomena.

ISSN:0021-8979    

DOI:10.1063/1.326798

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The measurements of magnetostriction and anisotropy of r.f. sputtered amorphous Gd1−xCoxthin films are reported. Both were measured in the range of composition x=0.667–0.835 using cantilever‐capacitance method. The perpendicular anisotropy Kuand saturation magnetostriction &lgr;sreach extremal values in the vicinity of the compensation composition (for x=0.77), although Kushows a minimum of ∼1×105erg/cm3, whereas (3/2) &lgr;sshows a maximum of ∼47×10−6. The experimental results are analysed within the frame of pair ordering model. A mechanism explaining the compositional dependence of magnetostriction is proposed.

ISSN:0021-8979    

DOI:10.1063/1.326799

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The coexistence of two minima in the anisotropy energy of a ferromagnetic crystal allows irreversible rotations of the magnetization vector to occur at a critical value Hcrof the applied magnetic field. These first order magnetization processes (FOMP) are in fact similar to the spin reorientation transitions that take place between different easy directions with changing temperature. The study of FOMP allows precise determinations of the anisotropy constants to be carried out if one knows the relations with the critical parameters. Previous papers give experimental evidence of FOMP in ferrites1and intermetallic2compounds together with a preliminary theoretical treatment. In the present work we carry out a complete analysis of this phenomenon in terms of the first three anisotropy constants Kiand coefficients &kgr;21,0, for a uniaxial crystal with field applied parallel or perpendicular to the symmetry axis. Analytical solutions have been found for the case of type 2 FOMP (when final state is below saturation) and for the boundary lines in the phase diagrams of easy directions and FOMP. Computer plots of the critical parameters vs. K2/K1, K3/K1andx4,0/x2,0,x6.0/x2.0, and application to the FOMP observed at 16 Tesla in the easy cone crystal PrCo5will be presented.1G. Astietal, IEEE Trans. MAG. 14, 883 (1978).2D. Melvilleetal, IEEE Trans. MAG 12, 1012 (1976).

ISSN:0021-8979    

DOI:10.1063/1.326801

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Using the technique of microwave transmission at FMAR, we have measured the temperature dependence of the Landau‐Lifshitz damping parameter &lgr; in nickel. It was found that the magnitude of &lgr; increased by a factor 4 over the temperature range 300 K–77 K. The microscopic theory of spin wave damping indicates that there are two contributions to the damping parameter; the one proportional to the resistivity and the other to the wave number dependent conductivity. We compare our experimental results with this theory and with the previous work of Bhagat using FMR.

ISSN:0021-8979    

DOI:10.1063/1.326802

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

Numerical calculations of the magnetic field dependence of the transmission of 24 GHz radiation through a 5 &mgr;m thick slab for a model ferromagnetic metal have been carried out using a non‐local relation between current and electric field, and using the Landau‐Lifshitz equations to describe the magnetization. A spherical Fermi surface corresponding to carriers having an effective mass ratio of 5.0 and mean free paths of 10.8 &mgr;m was used to represent the electrical response of the metal. For diffuse scattering of the carriers at the slab surfaces the transmission was found to be strongly peaked at the value of static field which corresponded to ferromagnetic resonance (FMR). This result suggests that the anomalously large transmission structure observed at FMR in pure nickel single crystals at helium temperatures1is an orbital effect due to the long mean free path of the current carriers.

ISSN:0021-8979    

DOI:10.1063/1.326803

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The generation and attenuation of phonons at ferromagnetic resonance has been studied both theoretically and experimentally. We have observed for the first time the effect of resonant reabsorption of phonons propagating through thick Ni films. The predictions of the theory are in very good agreement with experiment.

ISSN:0021-8979    

DOI:10.1063/1.326804

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

The results of an electron paramagnetic resonance (EPR) study of the effects of cold‐working (rolling and polishing) on the EPR spectrum of Er in Au are reported. Pellets of dilute alloys of Au doped with Er were prepared in an arc furnace. From the pellets, samples were made by rolling at room temperature. The resonance experiments were carried out at X‐band and at temperatures between 1.65 and 4.2 K. Heating of the rolled samples reduced the EPR linewidth and intensity and increased the asymmetry parameter (the A/B ratio). Gradual deformation by successive rolling resulted in almost complete recovery of the linewidth and A/B ratio to values observed before heating. No appreciable variations were detected in the g‐factor, hyperfine structure constant or the Korringa relaxation rate. Results are interpreted in terms of segregation of Er ions to subgrain boundaries. The EPR of magnetic impurities in metals appears to be a promising technique for the study of interactions between the magnetic impurities and the defects produced by cold‐working.

ISSN:0021-8979    

DOI:10.1063/1.326805

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

We have performed electron paramagnetic resonance measurements in single crystals of Cd1−xMnxTe at 9 GHz between 1.6 and 290 K for a wide range of manganese content (0.0005?x?0.60). The temperature of the order‐disorder transition, Tc, and the critical exponent &agr;, were determined from the temperature dependence of the EPR linewidth. At x=0.2 we find a discontinuity in Tcsuggestive of a percolation critical point.

ISSN:0021-8979    

DOI:10.1063/1.326806

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

We analyze low‐temperature nuclear magnetic resonance in quasi‐one dimensional planar magnets. For configurations in which the static field is perpendicular to the hard axis we calculate the nuclear relaxation times T1and T2using linearized magnon theory. The dominant T2process is associated with the raman scattering of the long wavelength magnons. Longitudinal relaxation is brought about by a three‐magnon process. We also calculate the temperature and field dependence of the magnetization which is then matched with experimental data to determine the region of applicability of the theory in the field‐temperature plane. Our calculated values of T1and T2are compared with data obtained from CsNiF3and with the corresponding zero‐field predictions. Reasonable agreement is obtained between experiment and theory.

ISSN:0021-8979    

DOI:10.1063/1.326807

出版商:AIP    

年代:1979

数据来源: AIP

摘要:

We report some experimental results on the ferromagnetic relaxation in single crystals of In‐substituted BiCa VIG. These crystals, grown in our laboratory exhibit very attractive properties from the practical point of view, e.g. low anisotropy, low resonance linewidth and low saturation magnetization. We measured the temperature dependence of the resonance linewidth &Dgr;H at X‐band from liquid He to room temperature. It was found that there was a low‐temperature peak in &Dgr;H near 12 K. This is quite different from the results reported for many other garnets. We suggest that this is due to the ’’intra‐ionic slow relaxation’’ mechanism of the valence‐change vanadium ions in In‐BiCaVIG. The linewidth &Dgr;H was also measured as function of frequency from 0.5 GHz to 10 GHz and the Sparks‐Loudon‐Kittel two‐magnon linewidth peak was observed. In this frequency range, &Dgr;H had a general tendency to increase linearly with increasing frequency except in the vicinity of the peak.

ISSN:0021-8979    

DOI:10.1063/1.326808

出版商:AIP    

年代:1979

数据来源: AIP