Field-free magnetization reversal by spin-Hall effect and exchange bias

As the first magnetic random access memories are finding their way onto the market, an important issue remains to be solved: the current density required to write magnetic bits becomes prohibitively high as bit dimensions are reduced. Recently, spin–orbit torques and the spin-Hall effect in particular have attracted significant interest, as they enable magnetization reversal without high current densities running through the tunnel barrier. For perpendicularly magnetized layers, however, the technological implementation of the spin-Hall effect is hampered by the necessity of an in-plane magnetic field for deterministic switching. Here we interface a thin ferromagnetic layer with an anti-ferromagnetic material. An in-plane exchange bias is created and shown to enable field-free S HE-driven magnetization reversal of a perpendicularly magnetized Pt/Co/IrMn structure. Aside from the potential technological implications, our experiment provides additional insight into the local spin structure at the ferromagnetic/anti-ferromagnetic interface.

Future information storage technology may exploit electrical currents to write the states of ferromagnetic nanoelements via spin torque effects. Here, the authors demonstrate such behaviour promoted by exchange bias from an interfaced antiferromagnet, which may help overcome practical device limitations.

Dual antiferromagnetic coupling at La0.67Sr0.33MnO3/SrRuO3 interfaces

We have studied the magnetic hysteresis cycle of La0.67Sr0.33MnO3/SrRuO3 antiferromagnetically coupled bilayers, by magnetometry and polarized neutron reflectometry. A positive exchange bias as well as an unusual asymmetry are observed on the magnetic reversal process of the La0.67Sr0.33MnO3 layer. Through an extended Stoner-Wohlfarth model comprising the magnetic anisotropy of both layers, we give experimental evidence that this asymmetry originates from two different but well-defined antiferromagnetic coupling strengths at the interface between the two magnetic oxides. The possible origin of this dual coupling is discussed in view of our experimental results.

[The importance of quantitative left ventriculography in coronary heart disease (author's transl)]

Regional impairment of left ventricular contraction in chronic stage of coronary artery disease is best demonstrated by using left ventriculography. Moreover, left ventricular volumes and ejection fraction can be computed from this angiography. Changes in these volumetric parameters are closely related to the degree of left ventricular dysfonction and to the adaptation mechanisms due to ventricular asynergy. Since left ventricular dysfonction has a high prognostic value in coronary artery disease (CAD), left ventricular volumes and ejection fraction should be measured as a routine of angiographic evaluation of CAD.

[The treatment of cardiac insufficiency using vasodilators (author's transl)]

Clinical applications involve heart failure during the acute phase of myocardial infarction, with the possibility of reducing the degree and extent of the perinecrotic ischaemic zone of the infarction. Treatment of this type would seem also to be particularly valuable in the provisional management of acute or sub-acute regurgitating valvular lesions: mitral insufficiency and interventricular communication secondary to an acute infarction, mitral and/or aortic regurgitation due the endocarditis. Finally, the results of oral vasodilators in the context of chronic refractory heart failure would seem ot be encouraging in the short term but their influence on long term prognosis is not known.

[The treatment of congestive heart failure by using vasodilators. I. Physiological basis. Different vasodilators (author's transl)]

The use of vasodilators represents a new approach in the treatment of heart failure. These drugs have the property of causing vasodilatation of either arterial or venous predominance or balanced between these two vascular beds. Arterio-dilators (phentolamine, hydralazine) increase stroke volume and cardiac output by decreasing ventricular afterload. Veno-dilators (nitroglycerine) have little effect on cardiac output but decrease ventricular filling pressure, thereby relieving pulmonary venous hypertension. Mixed vasodilators (Sodium nitroprussideate, trimetaphan) combine these two groups of properties in various degrees. The majority of these drugs can only be administered intravenously, with careful haemodynamic surveillance.

Pharmacokinetics of lidocaine after prolonged intravenous infusions in uncomplicated myocardial infarction

The kinetics of the elimination of lidocaine upon discontinuation of lidocaine infusions lasting more than 24 h were studied in 12 patients with uncomplicated myocardial infarctions. In this group of patients the mean half-life of the elimination phase was found to be 3.22 h. This is significantly different from the half-life of 100 min that has been reported after bolus injections or infusions lasting less than 12 h. This longer half-life should be taken into consideration in estimating the duration of toxicity and the rate of administration of the drug during and after intravenous infusions lasting 24 h or more.

External counterpulsation: coronary hemodynamics and use in treatment of patients with stable angina pectoris

External pressure counterpulsation (ECP) has been reported to improve the clinical status of patients with angina pectoris. To document the mechanisms for such an improvement left ventricular oxygen consumption and lactate metabolism, coronary sinus blood flow, and cardiac index were studied in 10 patients with angina pectoris 1) prior to and during ECP; and 2) during right atrial pacing before and after 4 consecutive 2-hour sessions of ECP treatment. During ECP peak early and mean arterial diastolic pressures were significantly raised above control values by 32 and 13% respectively. However, coronary sinus blood flow, left ventricular oxygen consumption and left ventricular lactate extraction, mean systolic arterial pressure and cardiac index were not significantly altered by ECP. Right atrial pacing at 140 beats/min increased coronary sinus blood flow 70% over control values and induced angina and ischemic ST segment changes in 8 patients before and after 4 consecutive treatments of ECP. ECP treatment did not significantly modify the above metabolic and hemodynamic responses at rest or during atrial pacing. Although 5 patients reported improvement in angina symptoms the effect was transitory. No significant improvement over pre ECP-treatment exercise angina threshold was observed immediately following or at 1 and 3 months post treatment. This method of noninvasive circulatory assistance appears to be of doubtful value in the management of patients with stable angina pectoris.

Hemodynamic findings in Friedreich's ataxia

Thirteen patients with classical Friedreich's ataxia underwent cardiac catheterization with recordings of retrograde cardiac pressures, measurements of cardiac output and calculation of the left ventricular volumes and mass. The cardiomyopathy in Friedreich's ataxia falls into the hypertrophic group of cardiomyopathies with decreased compliance of ventricular myocardium, varying degrees of concentric and asymmetric hypertrophy and outflow tract obstruction. Although there is no clear parallel between the degree of abnormal hemodynamic findings and the degree of neurological impairment, severely handicapped patients may present a diffusely hypertrophied and hypokinetic left ventricular myocardium.

Cardiological signs and symptoms in Friedreich's ataxia

The cardiovascular signs and symptoms were recorded in 36 patients with typical Friedreich's Ataxia (Group Ia, Ib). Seventeen patients were asymptomatic and this did not correlate with the severity of the disease. No pathognomonic clinical constellation was found to reveal the underlying cardiomyopathy.

Influence of left ventricular function on survival 3 to 4 years after aortocoronary bypass

Preoperative left ventricular ejection fraction (EF) was calculated using single plane cineventriculography in 93 patients in whom aortocoronary bypass surgery was performed before July 1970. Preoperative EF (mean plus or minus SEM) was 0.29 plus or minus 0.04 in 9 patients deceased between 2 and 35 mth after operation, significantly lower (p less than 0.001) than EF of 84 patients having survived 3 yr or more (0.55 plus or minus 0.02). The 3- to 4-yr mortality in these patients was 22.2% when preoperative EF was less than 0.50 and 1.75% when it was greater than or equal to 0.50 (p less than 0.01). Likewise, late mortality rose to 43.7% when EF was less than 0.40, compared to 2.6% when it was greater than or equal to 0.40 (p less than 0.005). In 21 patients in this series, left ventricular volumes and EF showed no significant difference before, approximately one year and between 3 and 4 yr after operation. This included 9 patients with normal or near normal contraction and 12 patients with impaired ventricular contraction preoperatively. Thus, in this study, preoperative EF was a major determinant of long-term prognosis after aortocoronary bypass and EF was not improved between 3 and 4 yr postoperatively. These data suggest, then, that in order to enhance survival after aortocoronary bypass, patients should be operated on before significant myocardial damage has occurred.