Efficient Spin Torques in Antiferromagnetic CoO/Pt Quantified by Comparing Field- and Current-Induced Switching.

We achieve current-induced switching in collinear insulating antiferromagnetic CoO/Pt, with fourfold in-plane magnetic anisotropy. This is measured electrically by spin Hall magnetoresistance and confirmed by the magnetic field-induced spin-flop transition of the CoO layer. By applying current pulses and magnetic fields, we quantify the efficiency of the acting current-induced torques and estimate a current-field equivalence ratio of 4×10^{-11} T A^{-1} m^{2}. The Néel vector final state (n⊥j) is in line with a thermomagnetoelastic switching mechanism for a negative magnetoelastic constant of the CoO.

Mechanism of Néel Order Switching in Antiferromagnetic Thin Films Revealed by Magnetotransport and Direct Imaging.

We probe the current-induced magnetic switching of insulating antiferromagnet-heavy-metal systems, by electrical spin Hall magnetoresistance measurements and direct imaging, identifying a reversal occurring by domain wall (DW) motion. We observe switching of more than one-third of the antiferromagnetic domains by the application of current pulses. Our data reveal two different magnetic switching mechanisms leading together to an efficient switching, namely, the spin-current induced effective magnetic anisotropy variation and the action of the spin torque on the DWs.

Spin structure and spin Hall magnetoresistance of epitaxial thin films of the insulating non-collinear antiferromagnet SmFeO3.

We report a combined study of imaging the antiferromagnetic (AFM) spin structure and measuring the spin Hall magnetoresistance (SMR) in epitaxial thin films of the insulating non-collinear antiferromagnet SmFeO3. X-ray magnetic linear dichroism photoemission electron microscopy measurements reveal that the AFM spins of the SmFeO3(1 1 0) align in the plane of the film. Angularly dependent magnetoresistance measurements show that SmFeO3/Ta bilayers exhibit a positive SMR, in contrast to the negative SMR expected in previously studied collinear AFMs. The SMR amplitude increases linearly with increasing external magnetic field at higher magnetic fields, suggesting that field-induced canting of the AFM spins plays an important role. In contrast, around the coercive field, no detectable SMR signal is observed, indicating that the SMR of the AFM and canting magnetization components cancel out. Below 50 K, the SMR amplitude increases sizably by a factor of two as compared to room temperature, which likely correlates with the long-range ordering of the Sm ions. Our results show that the SMR is a sensitive technique for non-equilibrium spin systems of non-collinear AFMs.

Tunable long-distance spin transport in a crystalline antiferromagnetic iron oxide.

Spintronics relies on the transport of spins, the intrinsic angular momentum of electrons, as an alternative to the transport of electron charge as in conventional electronics. The long-term goal of spintronics research is to develop spin-based, low-dissipation computing-technology devices. Recently, long-distance transport of a spin current was demonstrated across ferromagnetic insulators1. However, antiferromagnetically ordered materials, the most common class of magnetic materials, have several crucial advantages over ferromagnetic systems for spintronics applications2: antiferromagnets have no net magnetic moment, making them stable and impervious to external fields, and can be operated at terahertz-scale frequencies3. Although the properties of antiferromagnets are desirable for spin transport4-7, indirect observations of such transport indicate that spin transmission through antiferromagnets is limited to only a few nanometres8-10. Here we demonstrate long-distance propagation of spin currents through a single crystal of the antiferromagnetic insulator haematite (α-Fe2O3)11, the most common antiferromagnetic iron oxide, by exploiting the spin Hall effect for spin injection. We control the flow of spin current across a haematite-platinum interface-at which spins accumulate, generating the spin current-by tuning the antiferromagnetic resonance frequency using an external magnetic field12. We find that this simple antiferromagnetic insulator conveys spin information parallel to the antiferromagnetic Néel order over distances of more than tens of micrometres. This mechanism transports spins as efficiently as the most promising complex ferromagnets1. Our results pave the way to electrically tunable, ultrafast, low-power, antiferromagnetic-insulator-based spin-logic devices6,13 that operate without magnetic fields at room temperature.

Electric field control of magnetic properties and electron transport in BaTiO3-based multiferroic heterostructures.

In this paper, we report on a purely electric mechanism for achieving the electric control of the interfacial spin polarization and magnetoresistance in multiferroic tunneling junctions. We investigate micrometric devices based on the Co/Fe/BaTiO3/La0.7Sr0.3MnO3 heterostructure, where Co/Fe and La0.7Sr0.3MnO3 are the magnetic electrodes and BaTiO3 acts both as a ferroelectric element and tunneling barrier. We show that, at 20 K, devices with a 2 nm thick BaTiO3 barrier present both tunneling electroresistance (TER = 12 ± 0.1%) and tunneling magnetoresistance (TMR). The latter depends on the direction of the BaTiO3 polarization, displaying a sizable change of the TMR from -0.32 ± 0.05% for the polarization pointing towards Fe, to -0.12 ± 0.05% for the opposite direction. This is consistent with the on-off switching of the Fe magnetization at the Fe/BaTiO3 interface, driven by the BaTiO3 polarization, we have previously demonstrated in x-ray magnetic circular dichroism experiments.

[Pre-dialysis arteriovenous fistula results in better patency rate]. / Fistola artero venosa pre-dialisi = migliori risultati.

BACKGROUND: The timing of creation of the first permanent vascular access is crucial to the clinical history of haemodialysis patients. Our strategy is to create vascular access early enough to allow its maturation before the start of the treatment. METHODS: Aim of the study is to evaluate patency of primary A-V fistulas in patients treated between 1985 and 2000 in our dialysis unit. One hundred and thirty A-V fistulas created before haemodialysis treatment (range 10-540 days) and used at its beginning (pre-HD group) are compared with 74 A-V fistulas created and/or used after the start of the haemodialysis treatment (post-HD group). RESULTS: Pre-HD group fistulas resulted in higher patency rate than the post-HD group, immediately at the start of the treatment (94.6% vs. 86.5%, p<0.05), at 6 months (89.2% vs. 75.6%, p<0.025), at 12 months (84.5% vs. 64.6%, p< 0.005), at 24 months (77.2% vs. 54.8%, p< 0.005). CONCLUSIONS: A-V fistula is to be preferred in the choice of primary vascular access for chronic haemodialysis patients. It should be created early enough before the beginning of the treatment (when serum creatinine reaches 6 to 7 mg/dL). This planning avoids central venous catheter placement, preserves vessels and the choice of the best surgical option thus resulting in a better fistula survival.

Effects of different dialysis membranes on lipid and lipoprotein serum profiles in hemodialysis patients.

We measured the serum concentrations of a variety of lipid constituents--total cholesterol, triglycerides, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein cholesterol, apolipoproteins A1 and B, and lipoprotein(a)--in well-matched uremic patients undergoing chronic hemodialysis with either cuprophane (n = 13) or polysulfone (n = 13) membranes. We found that the patients on polysulfone membrane dialysis had significantly higher mean HDL cholesterol and apolipoprotein A1 concentrations than the patients on cuprophane membrane dialysis. There were no significant differences in the other variables studied. Moreover, polysulfone membrane dialysis was associated with a lower prevalence of potentially atherogenic lipid abnormalities such as low HDL cholesterol levels and high total cholesterol/HDL cholesterol rations. We concluded that the use of more physiological dialysis procedure may improve, in the long term, lipid and lipoprotein profiles in hemodialysis patients, though the exact mechanism(s) remains unknown.

Serum lipoprotein(a) and coronary artery disease in uremic patients on chronic hemodialysis.

There is convincing clinical and experimental evidence to support the notion that lipoprotein(a) [Lp(a)] is atherogenic. Patients undergoing chronic hemodialysis have an increased risk of atherosclerotic cardiovascular complications. In the present study, we investigated the possible relation between the alteration, if any, in serum Lp(a) and coronary artery disease in such patients. The mean serum concentration of Lp(a) tended to be higher in the 64 hemodialysis patients than in the 30 normal controls (15.1 +/- 15.2 vs. 9.7 +/- 10.4 mg/dl). However the difference did not reach statistical significance. The prevalence of levels above 30 mg/dl was 14% (9/64) and 10% (3/10), respectively, and the difference was also not statistically significant. Eleven hemodialysis patients with coronary artery disease had a significantly higher mean serum concentration of Lp(a) than the unaffected 53 (33.7 +/- 18.4 vs. 11.1 +/- 11.2 mg/dl, p < 0.001). Elevated levels were present in 63.6% (7/11) and 3.8% (2/53), respectively (p < 0.01). Other parameters of lipid metabolism were not different between the two groups. We observed statistically significant positive correlations of Lp(a) to total cholesterol, LDL cholesterol and apolipoprotein B in controls, in hemodialysis patients as a whole and in those without coronary artery disease. No such correlations were obtained when hemodialysis patients with coronary artery disease were analysed separately. It is concluded that firstly, high serum levels of Lp(a) in hemodialysis patients are strongly associated with coronary artery disease, as well as in the general population; and secondly, abnormalities in the metabolism of Lp(a) may underlie atherogenesis in these patients, independently of alterations in other lipid constituents.

Serum alpha-1-antitrypsin in hemodialysis patients with dialysis arthropathy.

Dialysis arthropathy is the most prominent dialysis-related amyloidosis feature. Alpha-1-antitrypsin (alpha-1-proteinase inhibitor) is the major circulating antiprotease. Twenty-three otherwise uncomplicated hemodialysis patients with well-documented dialysis arthropathy had a significantly (p < 0.05) lower serum mean concentration, 1,960 +/- 410.4 mg/l of alpha-1-antitrypsin than 47 patients with no joint symptoms who had a mean concentration of 2,256.6 +/- 424.5 mg/l. Decreased levels of the substance were detected in 13 (56.5%) of the 23 patients with dialysis arthropathy and in 13 (27.6%) of those 47 with no joint symptoms, the incidence in the former group being significantly (p < 0.05) higher than in the latter. In the dialysis arthropathy group, serum alpha-1-antitrypsin levels correlated inversely (r = -0.54, p < 0.01) with the dialysis duration and directly (r = 0.413, p < 0.05) with the corresponding beta-2-microglobulin determinations. We speculate that reduced antiprotease activity may play a role in amyloidogenesis in the setting of long-term hemodialysis.

Nephrotic-range proteinuria in a patient with high renin hypertension: effect of treatment with an ACE-inhibitor.

A 65-year-old man presented proteinuria in the nephrotic range that occurs in the setting of high renin hypertension. Proteinuria persisted after normalizing blood pressure by nifedipine. In contrast, treatment with an ACE-inhibitor (enalapril) resulted in the prompt resolution of the proteinuria. Interestingly, proteinuria relapsed after removing the ACE-inhibition. These observations suggest a causal relation between the overactivity of the renin-angiotensin system in this patient and his proteinuria.