Kazuaki Fukamichi

Itinerant electron metamagnetism in YCo2

Abstract The magnetization measurement of an exchange-enhanced Pauli paramagnet YCo2 has been made at 10 K in pulsed ultra-high magnetic fields up to 94 T to examine the existence of itinerant electron metamagnetism. The field induced phase transition from a paramagnetic to a ferromagnetic state has been observed for the first time at about 70 T, indicating a clear evidence for the existence of metamagnetism.

Itinerant electron metamagnetism in YCo2 and LuCo2

The magnetization curves have been measured for YCo 2 and LuCo 2 in ultra-high magnetic fields up to 100 T to examine the occurrence of itinerant electron metamagnetism. The metamagnetic transition has successfully been observed for the first time in both materials at about 70 T.

Spin Dynamics in the Amorphous Invar Alloy of Fe86B14

The spin waves in an amorphous Invar alloy Fe 86 B 14 11 , have been studied by inelastic neutron scattering. Well defined magnon groups were detected around (0, 0, 0) up to q =0.12 A -1 for various temperatures below T ≤0.9 T c . The spin waves show the dispersions \( \hbar \omega _{q}(T)=E_{0}(T)+D(T)q^{2}\) with D ( T ) varying with temperature according to D ( T )= D (0)(1- a T 5/2 ) with D (0)=118 ±6 (meV A 2 ). The spin wave stiffness at 0 K, D (0), thus determined is almost twice as large as the value D M (0)=68 ±2 (meV A 2 ) determined for the same sample by a magnetization measurement. The spin wave linewidth \( \varGamma \) varies with wave vector q as \(\varGamma=aq^{2}\) and it shows only limited temperature dependence. All of these features are quite similar to those found in the crystalline Invar alloys as Fe 65 Ni 35 and Fe 3 Pt.

Giant Magnetoresistance in Cu–Co Alloys Produced by Liquid Quenching

Giant magnetoresistance (GMR) in Cu-Co alloys produced by liquid quenching has been confirmed. A supersaturated solid solution was obtained in a quenched state and fine-grained magnetic precipitates in fcc Cu-rich matrix were obtained upon annealing. It has been found that Cu80Co20 alloy annealed at 500°C for 1 h exhibits a giant magnetoresistance ratio as large as 4% at room temperature.

Itinerant electron metamagnetism and spin fluctuations in nearly ferromagnetic metals Y(Co1-xAlx)2

High-field magnetisation- and temperature-dependent susceptibility of Laves phase inter-metallic compounds Y(Co1-xAlx)2 are investigated in the strongly exchange-enhanced paramagnetic region (0<or=x<or=0.11) in pulsed magnetic fields up to 100 T. In the whole concentration range, a sharp metamagnetic transition is observed in the low-temperature magnetisation process, while the low-field susceptibility exhibits a maximum at finite temperatures. The transition field Bc and the temperature of the susceptibility maximum Tmax obtained as a function of x indicate a linear relationship, i.e. Bc/Tmax=constant. The result clearly suggests that the susceptibility maximum of the nearly ferromagnetic metals is strongly correlated with itinerant electron metamagnetism.

High field magnetization of the Laves phase compounds M(Co1−xAlx)2 (M = Y, Lu)

Abstract Magnetization measurements have been carried out on the Laves phase compounds M(Co 1− x Al x ) 2 (M = Y, Lu) up to 42 T. Sharp metamagnetic transitions with small hysteresis are found in Y(Co 1− x Al x ) 2 , while broad transitions with large hysteresis are found in Lu(Co 1− x Al x ) 2 . The results suggest that the former compounds are magnetically homogeneous but the latter inhomogenous.

Neutron Diffraction and Isotropic Volume Expansion Caused by Deuterium Absorption into La(Fe0:88Si0:12)13

The crystal structures and magnetic properties of La(Fe 0.88 Si 0.12 ) 13 D 1.5 and La(Fe 0.88 Si 0.12 ) 13 H 1.6 have been investigated. The powder neutron diffraction declared that the compound La(Fe 0.88 Si 0.12 ) 13 D 1.5 has a cubic NaZn 13 -type structure of the F m \bar3 c space group in analogy with La(Fe 0.88 Si 0.12 ) 13 . The deuterium atoms in the compound La(Fe 0.88 Si 0.12 ) 13 D 1.5 occupy the interstitial 24 d site surrounded by two La atoms and four icosahedral clusters. The x-ray diffraction data of La(Fe 0.88 Si 0.12 ) 13 H 1.6 are also consistently explained by the same site of hydrogen atom. The deuterium or hydrogen absorption brings out a notable increase of the Curie temperature T C . The neutron diffraction of the compound La(Fe 0.88 Si 0.12 ) 13 D 1.5 shows that the magnetic structure is ferromagnetic and the average magnetic moment per Fe is about 2.2 µ B , almost the same as that of La(Fe 0.88 Si 0.12 ) 13 . Such behaviors can be explained as characteristic magnetovolume effect...

The structure of short- and medium-range order of Fe-rich amorphous Fe-La alloys

The ferromagnetic state of iron-rich amorphous FexLa1-x alloys (a-FexLa1-x) is known to become unstable with increasing iron concentration and at x=0.9 a cusp characteristic of a spin glass appears in the AC susceptibility. In order to elucidate the correlations between the magnetic properties and the structure, the authors measured both large-angle and small-angle X-ray scatterings for a-FexLa1-x(0.65<or=x<or=0.9) alloys. From large-angle scattering measurements, interatomic distances and partial coordination numbers between Fe-Fe, Fe-La and La-La atoms were determined. The Fe-Fe interatomic distances for these alloys are all very close to the critical value (=2.54 AA) at which an antiferromagnetic exchange competes with a ferromagnetic one. The Fe-Fe coordination number of 8.6 for a-Fe0.9La0.1was found to be close to 8.8 for crystalline (Fe0.86Al0.14)13La alloy where the ferromagnetic ordering collapses and the antiferromagnetic one dominates. The small-angle scattering for a-Fe0.9La0.1 shows pronounced high intensity in contrast to those for others (x=0.7 and 0.8). This fact suggests that inhomogeneous regions exist in a-Fe0.9La0.1. From the correlation function gamma (r) and Q-invariant 2 pi 2 gamma (0), the authors conjecture that the inhomogenous regions consist of iron clusters whose size is widely distributed and their volume fraction is estimated to be about 2%. The correlations of iron clusters with the spin glass state of a-Fe0.9La0.1 are discussed.

Giant Magnetoresistance in Bulk Cu-Rich Co–Cu, Co–Ni–Cu and Fe–Ni–Cu Granular Alloys

Magnetoresistance has been investigated for bulk Cu-rich Co–Cu and Co–Ni–Cu and Fe–Ni–Cu granular alloys prepared by aging and plastic deformation. Giant magnetoresistance (GMR) is observed in these bulk alloys in the process of phase separation and anisotropy in GMR for Fe5Ni15Cu80 alloy aged at 500° C for 170 min is obtained by compression.

Mictomagnetism and Magnetic After-Effect in Fe–Hf Amorphous Alloys

Magnetization in high magnetic fields, thermomagnetization curves at low fields, hysteresis loops after field cooling and magnetic after-effect in the initial magnetization region have been investigated for Fe–Hf amorphous alloys containing 7.5–39 at.%Hf. The present results indicate the mictomagnetism or the Fe-rich alloys and the normal ferromagnetism of the alloys containing above 20 at.%Hf. The magnetic after-effect in the mictomagnetic alloys is explained on the basis of the thermal fluctuation theory using a domain wall pinning model.