摘要:

An extensive investigation has been made of the antiferromagnetic resonance relaxation by AFMR linewidth observations inMnF2at microwave frequencies (20–75 GHz) and temperatures between 1.5°K and 40°K. At low temperatures (≲ 6°K) temperature independent, Lorentzian resonance lines with halfwidths of as small as 3 Oe for the uniform mode and 0.2 Oe for magnetostatic modes have been seen. They depend in detail on sample shape and orientation, surface preparation and impurity concentrations and allow identification of the primary relaxation mechanism ‐‐ a Tp2‐like two‐magnon scattering into the degenerate spin‐wave manifold via various lattice imperfections — in good agreement with the Loudon‐Pincus theory. The temperature dependent part of the linewidth can be approximately described by a T4power law, presumably arising from magnon‐magnon or magnon‐phonon scattering. The line profile and position of the AFMR were found to be strongly power dependent at moderate microwave power levels. The relaxation time of the longitudinal component of the magnetization, Mz, induced by high power AFMR absorption, has been directly measured between 1.5° and 8°K by detection of the change in the magnetization through the voltage induced in a pick‐up coil. The relation of our observations to those hitherto unexplained AFMR linewidths is discussed.

ISSN:0094-243X    

DOI:10.1063/1.2946971

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Mo¨ssbauer spectroscopy has been used to study single iron atoms (monomers) and groups of iron atoms trapped in a frozen rare‐gas matrix. Matrix isolated Fe(3d64s2) and Fe+(3d7) give two new calibration points for the &psgr;2(0) vs isomer shift relationship. These data yield&Dgr;R/R = − (8.7±0.3) × 10−4for the 14.4 KeV transition in Fe‐57. The observed l/T temperature dependence of the monomer line‐width shows that the direct phonon process is dominant in the spin‐lattice relaxation time. Spin‐lattice relaxation times of the order of2.5 × 10−10 secat 4.2K are obtained by assuming a hyperfine field of1.1 × 106 Oeat the Fe‐57 nucleus due to an iron atom with unquenched orbital momentum. We observe the quadrupole splitting of theI = 3/2excited state of Fe‐57 in the axial field produced by an iron nearest neighbor. At iron atom concentrations above about 5 percent, the magnetic hyperfine field at the Fe‐57 nucleus is very close to the field observed in iron metal.

ISSN:0094-243X    

DOI:10.1063/1.2947010

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The magnetic properties of the neptunium monopnictidesNpN,NpP,NpAs, andNpSb, determined by magnetization and Mo¨ssbauer effect measurements, are summarized. The magnetic structures change from ferromagnetic inNpNto longitudinal wave (LW) inNpPand probably inNpAsto simple antiferromagnetic inNpSb. The systematic variation of the magnetic structure and the existence of LW order indicates that the exchange interaction between the magnetic ions must be long range and oscillatory in real space.

ISSN:0094-243X    

DOI:10.1063/1.2947032

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Neptunium phosphide has theNaCl‐type structure with a lattice parameter ofa = 5.610 A. The compound orders antiferromagnetically at 120°K. Between 120 and 74°K, the magnetic moments are arranged in a longitudinal sinusoidal modulation with the spin direction parallel to the cube axis, and with a constant repeat distance of2.78±0.08unit cells. Below 74°K the spin structure becomes commensurate with the lattice, having a repeat of 3 unit cells, and higher‐order harmonics in the neutron pattern indicate a tendency towards forming a square 3+, 3− wave. At 4.2°K, however, the process is incomplete, the two neptunium magnetic moments being 2.4 and 1.8 &mgr;g. The Mo¨ssbauer spectra at 4.2°K can be explained by assuming two different hyperfine fields of3690±40 kOeand4210±40 kOeat the Np site, with an occupation ratio of two to one. This interpretation is in agreement with the neutron results. Magnetization and resistivity measurements both indicate transitions at 120°K (TN), and 74°K. The resistivity falls sharply at 74°K, and such a change is compatible with the decrease in magnetic scattering that occurs when the ordering becomes commensurate.

ISSN:0094-243X    

DOI:10.1063/1.2947044

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

According to recent theories, a portion of the longitudinal fluctuation in a uniaxial antiferromagnet below Tcis coupled to the energy density fluctuation. Since the latter may be calculated from experimental data, it is of interest to provide an accurate absolute calibration of the critical inelastic neutron scattering data. To do this, we have followed the transverse (magnon) scattering over the equivalent of a full nuclear Brillouin zone, extending in particular from (100) to close to the (200) position. This yields the transverse susceptibility &khgr;⊥(K). The data were corrected for the variation in the Mn2+form factor and the sample absorption. Since the (200) position corresponds to the accurately known uniform susceptibility, all the data may be put on an absolute basis. At 10°K, the ratio of the measured staggered susceptibility to the value inferred from spin‐wave theory (assuming an anisotropy field of 8800 Oe) is0.95 ± 0.04.

ISSN:0094-243X    

DOI:10.1063/1.2947055

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Neutron scattering measurements on both polycrystalline and single crystallineFeCl3were made near the phase transition at liquid helium temperatures. We found magnetic scattering in the ordered state to be consistent with the spiral structure proposed by Cable et al., in which the wave vector of the spiral is parallel to [1450]. The sublattice magnetization within the temperature range from 4.6°K to 7.945°K is described by(1−T/TN)&bgr;with&bgr; = 0.158 ± 0.005andTN = 8.060 ± 0.005°K, however at 7.98°K the magnetization falls nearly to zero from about 50% of its saturation value and displays a hysteresis, thus indicating a first order transition. Critical scattering was observed which indicated a predominantly three dimensional character.

ISSN:0094-243X    

DOI:10.1063/1.2947064

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

The resonance linewidths inEuSandEuSehave been measured at 24 GHz in the temperature interval 1.15–7 7K. The linewidth inEuSis independent of crystallographic orientation and exhibits the expected exchange narrowing, but without the abrupt narrowing at Tcobserved inEuO. The linewidth inEuSeincreases slowly with decreasing temperature to ∼12K exhibiting a broad maximum, decreases rapidly forT < 12K, and is anisotropic below 16K. The observed behaviour suggests an antiferromagnet with fluctuation broadening strongly suppressed by the applied field. The linewidth has been measured as a function of angle for the field in a (110) plane at different temperatures. The variation observed is not simply related to the angular dependence of the anisotropy energy and is not presently understood.

ISSN:0094-243X    

DOI:10.1063/1.2946736

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

An investigation of the far infrared absorption (&ngr;> 6 cm−1) of hematite (&agr;‐Fe2O3) was carried out at 4.2K in magnetic fields up to 60 kOe. The search for the (+H) branch of the antiferromagnetic resonance spectrum was complicated by the occurrence of rather pronounced dimensional resonances arising from electromagnetic interferences. A variety of asymmetric magnetic resonance transmission lines was observed. These are excellent examples of cases recently calculated by Rado in a general consideration of magnetic resonance, linewidths and lineshapes in the far infrared. The interferences were circumvented by the use of a composite wedge‐shaped crystal. From a combination of field‐sweeps and frequency‐sweeps the (+H) branch was well described starting atH=0,&ngr;=212 GHzand increasing linearly in H with the splitting factorg=2.00±0.02. The latter result is that expected for the S‐state ferric ion, and resolves a minor uncertainty from the millimeter microwave results.

ISSN:0094-243X    

DOI:10.1063/1.2946748

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

Investigations of certain chromium chalcogenide spinels have shown that the magnetic anisotropy K1of Cr3+ions is strongly positive and can be explained in terms of the spin Hamiltonian(1). It was hence interesting to find out the contribution from Cr3+to K1in a ferrimagnetic oxide such as YIG.

ISSN:0094-243X    

DOI:10.1063/1.2946754

出版商:AIP    

年代:1973

数据来源: AIP

摘要:

We present the main results of a new calculation on ferromagnetic resonance in magnetostrictive materials with&lgr;100 ≠ &lgr;111. The theory is based on the independent grain approach and is assumed to be valid when the anisotropy field, induced by isotropic planar strain (or stress), is of the same order of magnitude or larger than 4&pgr;M. The absorption spectra, as a function of the applied d.c. field, was calculated by integrating the individual crystallite absorptions and presents singularities when the applied field is equal to H100, H110and H111. The theory is used to explain the absorption spectra observed inNiFe2O4polycrystalline thin films, and the experimental results are compared with both the isotropic strain and stress hypothesis. Finally we determined the theoretical values of H100and H110with the applied field oblique to the film. The calculated curves agree fairly well with the experimental results.

ISSN:0094-243X    

DOI:10.1063/1.2946756

出版商:AIP    

年代:1973

数据来源: AIP