Hiroki Yamazaki

Magnetic relaxation in Ni wires

Abstract The magnetic relaxation in Ni wires has been investigated using a SQUID magnetometer. The magnetization M exhibited logarithmic dependence on time. The distribution of energy barriers was estimated from the temperature dependence of magnetic viscosity S = d M /d(log t ). Thermal excitation explains the field dependence of S - T curves except below 20 K. Below 20 K, macroscopic quantum tunneling and/or the interaction between Ni wires must be considered.

Reaction of N-acyl-α-methoxyamines with organozinc reagents. A convenient method for the synthesis of homoallylamines and β-amino esters

The reaction of N-acyl-α-methoxyamines with allyl-, propargyl-, and benzylzinc bromides and Reformatsky reagents proceeds in THF at room temperature. Homoallyl- and homopropargylamines and β-amino esters are synthesized in good yields.

Single crystal susceptibility of the S=1 one-dimensional Heisenberg antiferromagnet AgVP2S6

Abstract A reliable single crystal susceptibility data is reported to reveal the ground state property of the S = 1 one-dimensional Heisenberg antiferromagnet AgVP2S6. The observed susceptibilities for the parallel and perpendicular direction to the chain axis fall down rapidly as the temperature is lowered down to about 50 K, revealing a non-magnetic singlet ground state nature of the system. The results are interpreted quantitatively within the framework of the Haldane prediction, giving the quantum gap of E g k B ≈ 250 K which should be compared with 320 K from neutron scattering.

Correlation between the superconducting and structural properties in MgB2 thin films prepared by molecular-beam epitaxy

Superconducting MgB2 films were prepared on an Al2O3(0001) substrate by codeposition of Mg and B using the molecular-beam epitaxy technique and the effects of the growth conditions on the structural and the superconducting properties were extensively investigated. The superconducting transition temperature Tc shows a peak as a function of the deposition-rate ratio of Mg to B2 and the stoichiometric composition is likely realized at the Tc peak. The optimum substrate temperature Ts was found to be 330 °C. Detailed structural characterizations indicate the strong suppression of structural coherence in the stoichiometric and Mg-rich films. This accounts for the fact that optimized Tc (26.6 K) is still lower than bulk Tc like in previous molecular-beam epitaxy studies. We argue that such structural disorder originates from epitaxial strain due to the lattice mismatch between the film and the substrate.

Ferromagnetic resonance of evaporated Fe/Cu/Fe trilayers

Abstract A series of evaporated Fe(10 A)/Cu( d )/Fe(30 A) trilayers with Au buffer- and overlayer, where d = 10−68 A , is investigated by means of ferromagnetic resonance at room temperature. Comparison of the resonance fields calculated on a two-magnetization model and the observed resonance fields yields exchange coupling J as a function of d . A singularity in J in the vicinity of d = 20 A and a weak antiferromagnetic coupling for d > 40 A are observed. The problem of the systematic deviations of the observed resonance fields from the calculated resonance fields is encountered. A gradual change in the anisotropy fields in Fe layers as d increases can explain the deviations. Another explanation based on effective magnetization is also presented by way of trial.

Theoretical study of penetration reaction of fluorine atoms and ions into hydrogen-terminated Si(111) thin film

Abstract The interaction of fluorine atoms and ions with hydrogen-terminated Si(111) thin film has been studied using periodic ab initio electronic structure calculations. Penetration of fluorine atoms into the Si surface is found to be quite easy, and an interstitial fluorine atom can be situated directly behind the SiH bond while the original lattice structure, as well as the SiH bond itself, remains intact. The fluorine atom in this position is negatively charged by accumulating electron charges from the nearest silicon atoms. The penetration reaction of the fluorine ions into the Si surface is also found to be easy.

Interplay between superconductivity and ferromagnetism in epitaxial Nb(110)/Au(111)/Co(0001) trilayers

Epitaxially grown multilayer systems offer the possibility to study the influence of ferromagnetism on superconductivity in a controlled way. In this paper, we explore how the superconducting properties of high quality epitaxially grown superconductor/normal-metal/ferromagnet trilayers evolve as a function of the exchange splitting in the ferromagnet and the thickness of the normal-metal layer. We report results for Nb(110)/Au(111)/Co(0001) and make a detailed comparison with earlier results for Nb(110)/Au(111)/Fe(110). We use quantitative fast Fourier transform analysis to confirm the existence of a long-period (2.1 nm) oscillation in the superconducting transition temperature

Structural and magnetic properties of FeF2(001)/ZnF2(001) and FeF2(110)/ZnF2(110) superlattices

{T}_{\text{c}}

Interplay between superconductivity and ferromagnetism in epitaxial Nb

as a function of the Au-layer thickness

Competing magnetic anisotropies in Er/Tb multilayers

{t}_{\text{Au}}