Interlayer magnetic coupling interactions of two ferromagnetic layers by spin polarized tunneling

Magnetic interactions involving ferromagnetic layers separated by an insulating barrier have been studied experimentally on a fully epitaxial hard-soft magnetic tunnel junction: Fe/MgO/Fe/Co. For a barrier thickness below 1 nm, a clear antiferromagnetic interaction is observed. Moreover, when reducing the MgO thickness from 1 to 0.5 nm, the coupling strength increases up to J=-0.26 erg.cm(-2). This behavior, well fitted by theoretical models, provides an unambiguous signature of the interlayer exchange coupling by spin-polarized quantum tunneling.     

Interfacial resonance state probed by spin-polarized tunneling in epitaxial Fe/MgO/Fe tunnel junctions

The direct impact of the electronic structure on spin-polarized transport has been experimentally proven in high-quality Fe/MgO/Fe epitaxial magnetic tunnel junctions, with an extremely flat bottom Fe/MgO interface. The voltage variation of the conductance points out the signature of an interfacial resonance state located in the minority band of Fe(001). When coupled to a metallic bulk state, this spin-polarized interfacial state enhances the band matching at the interface and therefore increases strongly the conductivity in the antiparallel magnetization configuration. Consequently, the tunnel magnetoresistance is found to be positive below 0.2 V and negative above. On the other hand, when the interfacial state is either destroyed by roughness-related disorder or not coupled to the bulk, the magnetoresistance is almost independent on the bias voltage.     

Two-body photodisintegration of 3He and 4He in the Δ(1236) region

Differential cross sections for the reactions ³He(γ, p)d and ⁴He(γ, p)t were measured at proton c.m. angles of 60° and 90° for photon energies ranging from 150–450 MeV with an average resolution of 8 MeV. Bremsstrahlung was used as the photon source; deuterons/tritons were analyzed in a magnetic spectrometer whereas coincident protons were detected in a plastic scintillator telescope. The experimental method includes a calibration by means of ¹H(γ, π⁰)p differential cross section measurement at 90° c.m. in the same photon energy range. The ³He and ⁴He two-body photodisintegration differential cross sections show a monotonically decreasing variation with photon energy. In addition, partial data on the differential cross section of the reaction ⁴He(γ, n)τ at 90° and 120° neutron c.m. angle are given.     

Study of the γD → ppπ− reaction in the Δ(1236) region for well defined kinematical conditions

The γD → ppπ^? reaction cross section, in the Δ(1236) region, is measured in a counter experiment with high statistical accuracy. Particular emphasis is put on the accurate determination of the complete kinematics. For low values of the undetected nucleon momentum (p_r, ≈ 50 MeV/c), the validity of the spectator nucleon model is experimentally checked and the γn → pπ^? elementary reaction cross section is extracted and compared with other experimental data. When the recoiling nucleon momentum increases (p_r ≈ 150 MeV/c), significant departures from the spectator nucleon model are found. Presumably they are the signature of final state interaction effects.     

The nuclear magnetic moment of theI=2 80.56 keV Mössbauer level of166Er

A value for the nuclear magnetic moment of theI=2 (80.56 keV) level of¹⁶⁶Er has been obtained by comparing measurements made by the Mössbauer effect on¹⁶⁶Er with NMR measurements on the ground state of¹⁶⁷Er in the same matrix. From measurements on ErFe₂, ErAl₂ and ErZn we obtain the value _N (¹⁶⁶Er; 80.56 keV)=0.650±0.010 n.m. This result is slightly higher than previously proposed values.     

TmTO3 (T = Al, Fe, CrandV). A 169Tm Mössbauer study of magnetic and crystal field properties

¹⁶⁹Tm Mössbauer measurements are reported for the distorted perovskite compounds TmAlO₃, TmFeO₃, TmCrO₃ and TmVO₃ and have been analyzed to provide information concerning the crystal field and magnetic properties of the Tm³⁺ ion. Tm³⁺ has no magnetic moment in TmAlO₃ and low temperature saturated moments of 0.09, 0.8 and 2.1μ_B in TmFeO₃, TmCrO₃ and TmVO₃, respectively. In TmFeO₃ and TmCrO₃ the magnitudes and directions of the Tm³⁺ moments are examined in terms of previously proposed magnetic structural models. In TmVO₃, the crystal field properties are very different to those in the ferrite and chromite and a reorientation of the Tm³⁺ magnetic moments, accompanied by a sharp increase in their size, is observed near 10 to 15 K.     

Magnetic properties and domain structure of epitaxial (001) Fe/Pd superlattices

The magnetic properties of well-characterized (001)Fe/Pd superlattices prepared by molecular beam epitaxy are presented. The saturation magnetization is enhanced due to the polarization of the Pd interface, and analysis of hysteresis loops indicate low coercive fields, abrupt magnetic reversals, and ferromagnetic coupling between the Fe layers for all Pd thickness investigated (10–50 Å). It is also found that deposition on a stationary substrate can create a weak uniaxial in-plane anisotropy, which, for one of the two easy directions of Fe, causes a spontaneous rotation of the magnetization by 90° at low fields. This effect is clearly demonstrated by optical Kerr-effect imaging of the magnetic domain structure, and can be mistaken for antiferromagnetic coupling with very weak coupling fields. The strength of this uniaxial anisotropy is found to oscillate rapidly with Pd thickness, suggesting that it is very sensitive to the microstructure.