RESUMEN
A magnetic tunnel junction with a perpendicular magnetic easy-axis (p-MTJ) is a key device for spintronic non-volatile magnetoresistive random access memory (MRAM). Co-Fe-B alloy-based p-MTJs are being developed, although they have a large magnetisation and medium perpendicular magnetic anisotropy (PMA), which make it difficult to apply them to a future dense MRAM. Here, we demonstrate a p-MTJ with an epitaxially strained MnGa nanolayer grown on a unique CoGa buffer material, which exhibits a large PMA of more than 5 Merg/cm(3) and magnetisation below 500 emu/cm(3); these properties are sufficient for application to advanced MRAM. Although the experimental tunnel magnetoresistance (TMR) ratio is still low, first principles calculations confirm that the strain-induced crystal lattice distortion modifies the band dispersion along the tetragonal c-axis into the fully spin-polarised state; thus, a huge TMR effect can be generated in this p-MTJ.
RESUMEN
The magnetic properties of as-grown Ga1-xMnxAs have been investigated by the systematic measurements of temperature and magnetic field dependent soft x-ray magnetic circular dichroism (XMCD). The intrinsic XMCD intensity at high temperatures obeys the Curie-Weiss law, but a residual spin magnetic moment appears already around 100 K, significantly above the Curie temperature (T_{C}), suggesting that short-range ferromagnetic correlations are developed above T_{C}. The present results also suggest that the antiferromagnetic interaction between the substitutional and interstitial Mn (Mn_{int}) ions exists and that the amount of the Mn_{int} affects T_{C}.
RESUMEN
The chemical states of the ZnGeP(2):Mn interface which shows ferromagnetism above room temperature have been studied by photoemission spectroscopy. Mn deposition on the ZnGeP2 substrate heated to 400 degrees C induced Mn substitution for Zn and then the formation of metallic Mn-Ge-P compounds. Depth profile studies have shown that Mn 3d electrons changed their character from itinerant to localized along the depth, and in the deep region, dilute divalent Mn species (<5% Mn) was observed with a coexisting metallic Fermi edge of non-Mn 3d character. The possibility of hole doping through Mn substitution for Ge and/or Zn vacancy is discussed.
RESUMEN
To clarify the effects of nifedipine and enalapril on cardiac autonomic nervous function during postural changes, power spectral analysis of heart rate variability and humoral factors was performed during tilt tests before and after 3 months of drug administration. The study group consisted of 29 elderly patients with hypertension (mean age, 69 yr), who were divided into two groups: 15 patients received nifedipine (group N) and 14 received enalapril (group E). In group N, systolic blood pressure was significantly decreased and the percent changes in low-frequency coefficient of component variance, normalized low-frequency: high-frequency ratio, and plasma norepinephrine concentration were significantly altered by nifedipine administration. Group E, in contrast, showed no significant decrease in SBP, and only the percent change in high-frequency coefficient of component variance increased significantly after enalapril administration. These results suggest that cardiac autonomic nervous function is markedly impaired during the tilt test after long-term treatment with nifedipine, whereas it is well-maintained after long-term treatment with enalapril.
Asunto(s)
Inhibidores de la Enzima Convertidora de Angiotensina/efectos adversos , Sistema Nervioso Autónomo/efectos de los fármacos , Bloqueadores de los Canales de Calcio/efectos adversos , Enalapril/efectos adversos , Hipertensión/fisiopatología , Nifedipino/efectos adversos , Anciano , Anciano de 80 o más Años , Inhibidores de la Enzima Convertidora de Angiotensina/uso terapéutico , Presión Sanguínea/efectos de los fármacos , Bloqueadores de los Canales de Calcio/uso terapéutico , Método Doble Ciego , Enalapril/uso terapéutico , Femenino , Frecuencia Cardíaca/efectos de los fármacos , Hormonas/sangre , Humanos , Hipertensión/tratamiento farmacológico , Masculino , Persona de Mediana Edad , Nifedipino/uso terapéutico , Pruebas de Mesa InclinadaRESUMEN
To clarify the effect of the calcium antagonist Nifedipine and the ACE inhibitor Enalapril on cardiac autonomic activity, power spectral analysis of heart rate variability (PSA) was conducted in 39 elderly patients with essential hypertension (mean age: 63: +/- 11 years) before and after treatment. Twenty patients were treated with 10-20 mg of Nifedipine (N group) and 19 with 5 mg of Enalapril (E group) for 3 months. beta-blocker (Atenolol 12.5 mg) was added to Nifedipine in 12 patients of the N group for 1 month, and the modified effect of Atenolol on cardiac autonomic activity was also evaluated. Blood pressures were significantly reduced in both N and E groups after the treatment. The low frequency component (LF) in PSA, which was considered to be a quantitative marker of cardiac sympathetic activity, increased significantly and the high frequency component (HF), which was a marker of cardiac parasympathetic activity, significantly decreased with increase of PNA levels in N group after the treatment. However, the LF decreased significantly after addition of Atenolol. On the other hand, there was little significant change in LF and PNA in E group. These results suggest that Nifedipine increased cardiac sympathetic activity and that Enalapril had little influence on the cardiac sympathetic tone, while both antihypertensive agents significantly reduced blood pressure itself.