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ABSTRACT: We investigated the origin of perpendicular magneto-crystalline anisotropy (MCA) in L1(0)-ordered FeNi alloy using first-principles density-functional calculations. We found that the perpendicular MCA of L1(0)-FeNi arises predominantly from the constituent Fe atoms, which is consistent with recent measurements of the anisotropy of the Fe orbital magnetic moment of L1(0)-FeNi by means of x-ray magnetic circular dichroism. Analysis of the second-order perturbation of the spin-orbit interaction indicates that spin-flip excitations between the occupied majority-spin and unoccupied minority-spin bands make a considerable contribution to the perpendicular MCA, as does the spin-conservation term for the minority-spin bands. Furthermore, the MCA energy increases as the in-plane lattice parameter decreases (increasing the axial ratio c/a). The increase in the MCA energy can be attributed to further enhancement of the spin-flip term due to modulation of the Fe d(xy) and d(x(2) - y(2)) orbital components around the Fermi level under compressive in-plane distortion.
Journal of Physics Condensed Matter 02/2013; 25(10):106005. · 2.55 Impact Factor
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ABSTRACT: We investigated the spin-dependent transport properties of Fe/MgAl2O4/Fe(001)
magnetic tunneling junctions (MTJs) on the basis of first-principles
calculations of the electronic structures and the ballistic conductance. The
calculated tunneling magnetoresistance (TMR) ratio of a Fe/MgAl2O4/Fe(001) MTJ
was about 160%, which was much smaller than that of a Fe/MgO/Fe(001) MTJ
(1600%) for the same barrier thickness. However, there was an evanescent state
with delta 1 symmetry in the energy gap around the Fermi level of normal spinel
MgAl2O4, indicating the possibility of a large TMR in Fe/MgAl2O4/Fe(001) MTJs.
The small TMR ratio of the Fe/MgAl2O4/Fe(001) MTJ was due to new conductive
channels in the minority spin states resulting from a band-folding effect in
the two-dimensional (2-D) Brillouin zone of the in-plane wave vector (k//) of
the Fe electrode. Since the in-plane cell size of MgAl2O4 is twice that of the
primitive in-plane cell size of bcc Fe, the bands in the boundary edges are
folded, and minority-spin states coupled with the delta 1 evanescent state in
the MgAl2O4 barrier appear at k//=0, which reduces the TMR ratio of the MTJs
significantly.
03/2012;
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ABSTRACT: We study electronic and transport properties of Co2MnSi/Co2MnAl/MgO(001) junctions on the basis of the first-principles density functional calculations. We found that an insertion of thin Co2MnAl layers into a Co2MnSi/MgO junction can eliminate interface states in the minority-spin gap and provide a 100% spin-polarization at the interface. A transfer of electrons from the minority- to majority-spin states of interfacial Mn atoms plays an important role to recover the half-metallic gap in the MnAl-terminated interface. Furthermore, the magnetic tunnel junction with Co2MnSi/(Co2MnAl)n/MgO(001) (n=1~3) retains coherent tunneling of the Δ1-band electrons in parallel magnetization, which is in contrast to that with Co2MnSi/(Co2CrAl)n/MgO(001) where the tunneling of the Δ1-band electrons is reduced significantly at the Co2CrAl layer.
Journal of Physics Conference Series 02/2010; 200(5):052016.
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ABSTRACT: The interface between the half-Heusler alloy CoFeSi and Si is investigated by using first-principles density-functional calculations. Although CoFeSi has not been fabricated yet, its formation energy turns out to be negative. Within the generalized gradient approximation, CoFeSi shows nearly half-metallic properties, and its lattice constant is about 5.38 Å; this value is relatively close to the lattice constant of Si. We here chiefly investigate the CoFeSi/Si (110) interface, and find that the half-metallic properties are almost preserved at a specific (110) interface. Furthermore, the interfacial structure which leads to the high spin polarization has the lowest energy of the (110) interfacial patterns examined in this work. The half-metallicity at the interfaces is similarly observed in the densities of states projected onto delocalized sp states, and this suggests the relevance of the high spin polarization to transport properties.
Journal of Physics Condensed Matter 02/2009; 21(6):064244. · 2.55 Impact Factor
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ABSTRACT: We investigate and discuss the effects of interfacial oxidation on electronic structures and tunnel conductance of the Co(2)MnSi/MgO/Co(2)MnSi(001) magnetic tunnel junction (MTJ) on the basis of first-principles calculations. It is found that the MnSi termination tends to be oxidized compared with the Co termination because of the relaxation of atomic positions in the MnSi-terminated interface. Furthermore, we found that the single oxide layer inserted on both sides of the junction greatly decreases the tunnel conductance of the MTJ in parallel magnetization. We concluded that the relaxation of the Mn atomic position in the oxidized junction reduces the coupling of the Δ(1) states between the Co(2)MnSi electrode and the MgO barrier and causes significant interfacial scattering of the majority-spin electrons with Δ(1) symmetry at the oxidized layer.
Journal of Physics Condensed Matter 02/2009; 21(6):064245. · 2.55 Impact Factor
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ABSTRACT: We have carried out electronic structure and transport calculations for magnetic tunnel junctions (MTJ) composed of MgO and a half-metallic full Heusler alloy Co(2)MnSi on the basis of the density functional theory and the Landauer formula. We find that the density of states of Co atoms at the Co(2)MnSi/MgO(001) interface shifts toward the higher energy side due to the reduced symmetry, leading to a reduction of the spin polarization at the interface. Furthermore, we show that the majority-spin transmittance as a function of the in-plane wavevector [Formula: see text] has a broad peak centred at [Formula: see text] due to the tunnelling from the Δ(1) channel of Co(2)MnSi, while the transmittance from the Δ(5) channel is three orders of magnitude smaller than that of the Δ(1) channel. These results indicate that coherent tunnelling through the Δ(1) band is dominant also in an MTJ with Co(2)MnSi and an MgO barrier, like in Fe/MgO/Fe(001) MTJ and related systems.
Journal of Physics Condensed Matter 09/2007; 19(36):365228. · 2.55 Impact Factor
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ABSTRACT: We investigate the effect of O or Be co-doping on the exchange interaction between Cr spins in (Ga, Cr)N by means of first-principles calculations based on the density-functional theory. The ferromagnetic exchange interactions are reduced by doping Be around Cr. On the other hand, O doping reduces the ferromagnetic interaction remarkably only for the case of Cr-O-Cr complex formation. The enhancement of the ferromagnetic exchange interaction cannot be achieved by doping O or Be impurities. However, the O and Be impurities can help the clustering of Cr atoms due to the enhancement of the attractive interaction between Cr atoms.
Journal of Physics Condensed Matter 09/2007; 19(36):365238. · 2.55 Impact Factor
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ABSTRACT: We perform the first-principles density functional calculations of Co-based full-Heusler alloys, exploring 25 possible combinations of Co <sub>2</sub>YZ ( Y= Ti , V, Cr, Mn, and Fe; Z= Al , Ga, Si, Ge, and Sn) in order to clarify the stability for the Co-related atomic disorder, because this type of disorder is considered to degrade the spin polarization of Co <sub>2</sub>YZ . We found that the disorder between Co and Y atoms correlates with the total valence electron charges around Y atom, because a difference in valence electron charges between Co and Y atoms leads to a different shape of the local potential at each site. This means that Ti-based alloys are better than Cr-, Mn-, and Fe-based alloys in preventing the atomic disorder between Co and Y atoms. From our results, we propose stable Co-based full-Heusler alloys with excellent prospects for half-metallic ferromagnets.
Journal of Applied Physics 05/2006; · 2.17 Impact Factor
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ABSTRACT: We evaluated the prevalence and risk factors for erectile dysfunction (ED) and interest in ED treatment among Japanese men being treated for type 2 diabetes mellitus. Patients (40-79 years; n=1118) completed the 5-item version of the International Index of Erectile Function (IIEF-5), and questions related to interest in ED pharmacotherapy, subjective symptoms of diabetes, and general quality of life. A separate survey completed by physicians examined the relationships between age, diabetic treatments (insulin or oral), symptoms of diabetes (poor glycemic control, microangiopathy), complications of diabetes (hypertension, ischemic heart disease, cerebrovascular disease), and ED. The prevalence of ED in patients with diabetes was 90%, a rate double that of non-diabetic individuals. Multivariate analyses revealed that age, insulin therapy, microangiopathy, hypertension, history of cerebrovascular or cardiovascular disease, leg dysesthesia, dysuria, insomnia, and anorexia all represented significant risk factors for ED. Half of all respondents were interested (29%) or would consider pharmacotherapy for ED (21%). These findings suggest that ED is a significant problem in Japanese men with diabetes, and that specific risk factors increase the prevalence of ED. Furthermore, the survey results expose national attitudes toward treatment of ED.
Diabetes Research and Clinical Practice 11/2005; 70(1):81-9. · 2.75 Impact Factor
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ABSTRACT: Zinc-blende half-metallic ferromagnets are promising materials in order to open up a new world of semiconductor spintronics.
We design a new class of half-metallic ferromagnets, the zinc-blende transition-metal mono-pnictides, using ab-initio calculations
based on the density-functional theory. The calculations show that the total-energy difference between the ferromagnetic and
the antiferromagnetic states for the zinc-blende CrAs is the largest among all the studied compounds and the highly spin-polarized
electronic band structure is almost unaffected from the spin-orbit interaction.We further study the properties of zinc-blende
CrAs/GaAs multilayers theoretically and show that they keep a high spin polarization. Experimental realization of the previously
nonexistent zinc-blende CrAs thin film has been achieved by molecular-beam epitaxy. The crystallographic analysis is presented
together with the magnetic properties of the epitaxial film. The morphological structure and the magnetic properties change
sensitively depending on the substrate temperature during the growth. The room-temperature saturation magnetization of the
film grown under optimum conditions reaches about 3 μB per formula unit, which agrees with the theoretically predicted value
and reflects the half-metallic behavior. The epitaxial growth of multilayers consisting of 2–4 monolayers of CrAs and 2–4
monolayers GaAs with atomically flat surfaces and interfacess is demonstrated.
09/2005: pages 293-311;
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ABSTRACT: We perform first-principles density functional calculations for Mn doped group-IV (Ge, Si) based diluted magnetic semiconductors. It is found that the ferromagnetic spin configuration is stabilized when two Mn atoms are located along the [110] direction in Ge and Si hosts due to the strong ferromagnetic exchange interaction between Mn impurities. Furthermore, our results show that a ferrimagnetic Mn cluster is more stable than the ferromagnetic Mn configuration along the [110] direction, indicating that Mn impurities tend to gather and create undesired magnetic clusters in Ge and Si hosts. We conclude that the vicinal Ge(111) and Si(111) surfaces play an important role in the growth process of Mn doped Ge and Si in obtaining a ferromagnetically stable Mn configuration.
Journal of Physics Condensed Matter 11/2004; 16(48):S5735. · 2.55 Impact Factor
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ABSTRACT: We have investigated theoretically the effects of atomic disorder on the electronic and magnetic structures of the full-Heusler alloy Co <sub>2</sub>( Cr <sub>1-x</sub> Fe <sub>x</sub>) Al using the first-principles density functional calculation with the Korringa–Kohn–Rostoker coherent-potential approximation. It was found that Co <sub>2</sub>( Cr <sub>0.6</sub> Fe <sub>0.4</sub>) Al preserves the high spin polarization even in the disordered B2 structure, where (Cr,Fe) and Al randomly occupy octahedral sites of the alloy. On the other hand, the disorder between Co and (Cr,Fe) considerably reduces the spin polarization. Furthermore, the total magnetic moment of Co <sub>2</sub>( Cr <sub>0.6</sub> Fe <sub>0.4</sub>) Al decreases with increasing disorder between Co and (Cr,Fe) due to the antiferromagnetic coupling of the antisite Cr with the ordinary site Cr. These results indicate that control of the disorder between Co and (Cr,Fe) is crucial in order to obtain highly spin polarized full-Heusler alloys Co <sub>2</sub>( Cr <sub>1-x</sub> Fe <sub>x</sub>) Al . © 2004 American Institute of Physics.
Journal of Applied Physics 07/2004; · 2.17 Impact Factor
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ABSTRACT: We investigate the properties of interfaces between highly spin-polarized zinc-blende (ZB) CrAs and GaAs using first-principles density functional calculations. It is found that the local spin polarization at the Fermi level is very high even at ZB-CrAs/GaAs interface and then exhibits gradual decay from the interface to the inside of GaAs, reflecting their ideal structural matching. We further study the properties of ZB-CrAs/GaAs multilayer where two-monolayer ZB-CrAs and two-monolayer GaAs stack alternately. The multilayer shows high spin polarization throughout its entire region. Since the spin polarization is found insensitive to Cr-Ga substitutional disorder, both ZB-CrAs and ZB-CrAs/GaAs multilayer may work as efficient filter for spin-polarized current injection into GaAs. © 2004 American Institute of Physics.
Journal of Applied Physics 05/2004; 95(11):6518-6520. · 2.17 Impact Factor
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ABSTRACT: To measure the prevalence of erectile dysfunction (ED) in community-based populations in Brazil, Italy, Japan, and Malaysia and to study its association with the demographic characteristics, medical conditions, and health-related behavior.
In each country, a random sample of approximately 600 men aged 40 to 70 years was interviewed using a standardized questionnaire. All the data were self-reported. ED was assessed by the participants' "ability to attain and maintain an erection satisfactory for sexual intercourse," and the men were classified as not having ED if they answered "always" and as having mild, moderate, or complete ED if they answered "usually," "sometimes," or "never," respectively.
The age-adjusted prevalence of moderate or complete ED was 34% in Japan, 22% in Malaysia, 17% in Italy, and 15% in Brazil. The overall age-specific prevalence of moderate or complete ED was 9% for men aged 40 to 44 years, 12% for 45 to 49 years, 18% for 50 to 54 years, 29% for 55 to 59 years, 38% for 60 to 64 years, and 54% for those 65 to 70 years. The increased risk of ED was associated with diabetes, heart disease, lower urinary tract symptoms, heavy smoking, and depression and increased by 10% per year of age. It was inversely associated with education, physical activity, and alcohol drinking.
ED is an international problem, the prevalence and severity of which increases with age. Despite national variations in prevalence, uniform associations were found between ED and medical conditions and lifestyle habits.
Urology 02/2003; 61(1):201-6. · 2.43 Impact Factor
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Masafumi Shirai
Nippon rinsho. Japanese journal of clinical medicine 07/2002; 60 Suppl 6:107-11.
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Masafumi Shirai
Nippon rinsho. Japanese journal of clinical medicine 07/2002; 60 Suppl 6:226-8.
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Masafumi Shirai
Nippon rinsho. Japanese journal of clinical medicine 07/2002; 60 Suppl 6:91-6.
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Masafumi Shirai
Nippon rinsho. Japanese journal of clinical medicine 07/2002; 60 Suppl 6:200-2.
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Masafumi Shirai
Nippon rinsho. Japanese journal of clinical medicine 07/2002; 60 Suppl 6:271-5.
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Masafumi Shirai
Nippon rinsho. Japanese journal of clinical medicine 07/2002; 60 Suppl 6:276-9.
