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.

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.

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.

Effects of renal substitutive programs on amino acid patterns in chronic uremia.

Abnormalities in the amino acid patterns are a constant finding in chronic renal failure and can be regarded as one of the typical biochemical alterations of uremia. This paper evaluates the long-term effects of various artificial substitutive treatments and renal transplantation on plasma and tissue amino acid patterns in chronically uremic patients. Fifty-three patients were included in the study: 35 on artificial treatments (9 on hemodialysis, 9 on hemofiltration, 4 on hemoperfusion, 6 on continuous ambulatory peritoneal dialysis, and 7 on intermittent peritoneal dialysis) and 18 with well-functioning renal transplants. Complete plasma aminograms were performed in all patients before starting the treatment, and repeated every 3 months up to 1 year (artificial therapies) and 3 years (renal transplantation). The amino acid composition of the bone was also determined in 8 dialysis patients and 9 transplant patients. None of the artificial therapies was associated with normal plasma patterns either in the short- or in the long-term, whereas successful renal transplantation led to normalization of the plasma profile within 2 to 4 months in all patients. However, bone amino acid composition remained altered both in artificially treated and in transplanted patients.

Effect of ibopamine on the progression of chronic renal failure.

Persistent changes in the slope of the reciprocal of serum creatinine concentration against time after medical intervention are likely to reflect the influence of therapy on progression of chronic renal failure. This observation allowed us to demonstrate the ability of ibopamine, a new orally active dopamine-related drug, to improve renal function or at least to slow its deterioration in 20 patients studied over a period of 6 months. We also noted that the therapeutic response to the drug varied considerably according to the nature of the underlying nephropathy, with maximal benefit being observed in nonglomerular diseases.

Serum CA 19-9 and CA 50 antigens in hemodialysis patients.

Serum concentrations of monoclonal antibody-defined tumor markers CA 19-9 and CA 50 were measured in 64 uncomplicated hemodialysis patients (Group 1) and in 8 hemodialysis patients with cancer (Group 2) in comparison with corresponding CEA determinations. From our results in Group 1 patients it appears that both CA 19-9 and CA 50 maintained an excellent specificity in these patients. As to the sensitivity of these tests, our findings in Group 2 patients are comparable with those reported in patients with cancer and normal renal function. It is concluded that, unlike CEA, these new tumor markers maintain their clinical value in chronic renal failure.

Elevated acute phase reactants in hemodialysis patients.

The incidence of elevated acute phase reactants, measured by nephelometry, was examined in 69 otherwise uncomplicated hemodialysis patients in comparison with 30 healthy subjects. Increased C-reactive protein was found in 40.6% of the patients (p less than 0.001 vs controls) and the degree of increase was correlated with the duration of hemodialysis. Haptoglobin was increased in 33.3% (p less than 0.01 vs controls). High levels of alpha-1-acid glycoprotein and alpha-1-proteinase inhibitor were present in 15.9% and 2.9%, respectively; these frequencies were not significantly different from controls. No differences between pre- and postdialysis values were observed. It is concluded that, unlike C-reactive protein, both alpha-1-acid glycoprotein and alpha-1-proteinase inhibitor maintain an excellent specificity in hemodialysis patients. Vice versa, haptoglobin may be unreliable as an acute phase reactant in these patients because of the unacceptably high false-positive rate.

Effect of different dialyzer membranes on serum angiotensin-converting enzyme during hemodialysis.

The effects of different dialyzer membranes on serum concentration of angiotension-converting enzyme (ACE) and white blood cells during hemodialysis were examined on a cross-over basis in 20 chronically uremic patients. Hemodialysis with cuprophane membranes was associated with a significant (p less than 0.001) fall in the mean leukocyte count during the 1st hour of treatment. The use of polymethylmethacrylate membranes resulted in a more attenuated form of leukopenia and with polyacrylonitrile membranes no change was observed during hemodialysis. Hemodialysis with each membrane caused a comparable, significant (p less than 0.005) increase in serum ACE, independent of the degree of leukopenia but significantly (p less than 0.001) correlated with the increases in serum proteins. We conclude that this increase in serum ACE concentration after hemodialysis does not reflect acute damage of the pulmonary vascular endothelium during treatment and most probably is a result of hemoconcentration. Therefore, serum ACE analysis is not an indicator of dialyzer membrane biocompatibility.

Regular hemoperfusion in regular dialysis treatment. A long-term study.

The capacity of activated charcoal to remove toxins from the blood is well established. Its poor biocompatibility, inability to remove urea, electrolytes and water, and high cost have so far been the major objection to a wider use of charcoal with chronic uremic patients. The availability of a charcoal coated by a new highly hydrophilic methacrylate based on membrane enabled us to keep 18 uremic patients on a combined hemodialysis-hemoperfusion schedule for 4-52 weeks. Investigations concerned patients in whom relapsing signs of uremia occurred despite technically adequate dialysis, and other cases where dialysis was both technically and clinically adequate. In the first group of patients, the combined programme led to an improvement of the dialysis resistant clinical signs, while certain positive metabolic effects were also observed. In the second group, the hemodialysis-hemoperfusion treatment allowed a reduction of about 30% in time of treatment per week. Tolerance of the new coated charcoal was good throughout treatment in terms both of biocompatibility and of side effects.

Red blood cell volume distribution width (RDW) in uraemic patients on chronic haemodialysis.

Red blood cell volume distribution width (RDW) was obtained with the Coulter counter in 60 haemodialysis patients and 55 normal individuals. RDW tended to be higher in the former and the degree of increase was to some extent correlated with the underlying nephropathy. Although RDW failed to correlate with conventional tests of iron status, it was observed that iron administration could produce a decrease toward normal in RDW and a parallel increase in haemoglobin when the initial RDW was increased. In contrast, the response to iron was negligible in the patients with normal RDW basally. It was concluded that high RDW is an acceptable indicator of iron deficiency in haemodialysis patients.

Immune response to a recombinant hepatitis B vaccine in hemodialysis patients.

A 20-microgram dose of a recombinant hepatitis B vaccine was given at 0, 1, 2 and 6 months to 24 hemodialysis patients. From month 7 (i.e., 1 month after the fourth injection), 58.3% (14/24) of the patients had developed protective levels of antibodies against hepatitis B surface antigen (anti-HBs). In patients responding to vaccination, the fourth injection led to an abrupt rise of the anti-HBs titres which reached their maximum 2 months later, that is, in month 8. At that time, the geometric mean titre of anti-HBs was 145.79 mlU/ml. Eighteen months after the start of vaccination, 50% (12/24) of the patients were maintaining protective levels of anti-HBs antibodies. It is noteworthy that these results could be obtained with a considerably lower dosage than previously recommended.

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.

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.

[Osteo-articular amyloidosis caused by dialysis. Clinical and radiologic aspects]. / Amiloidosi osteoarticolare da dialisi. Aspetti clinici e radiologici.

Twenty-nine patients who had received chronic hemodialysis for more than 5 years provided the material for the present study. In 12 of them (41%) there were radiological findings of dialysis related amyloidosis, mainly destructive spondyloarthropathy of the cervical spine (n = 11) and geodes of the shoulder (n = 5). When compared with negative patients, these patients were significantly older (p less than 0.001 and had been dialyzed for longer periods of time (p less than 0.01). Moreover, in such patients there was an higher incidence of carpal tunnel syndrome (p less than 0.025) and shoulder pain (p less than 0.001). Our results confirm that osteoarticular amyloidosis is a frequent long-term complication of chronic hemodialysis and underline the correlation between clinical and radiological findings.

[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.

[Significance of serum levels of beta-2-microglobulin in dialysis patients]. / Significato dei livelli sierici di beta-2-microglobulina nei pazienti in dialisi.

beta 2M has been shown to be a major constituent of the amyloid deposits developing in uremic patients undergoing long-term hemodialysis. In this study, serum levels of beta 2M were determined in 67 hemodialysis patients and a mean +/- SD concentration of 57.8 +/- 18.5 mg/L was obtained. There was no difference in the concentration of the substance between the patients with evidence of dialysis-related amyloidosis and those without it. Moreover, no correlation between beta 2M levels and duration of hemodialysis was found. Interestingly, the patients with residual diuresis had a significantly lower mean beta 2M concentration than the anuric patients (35.0 +/- 13.1 vs 62.8 +/- 15.8 mg/L, p less than 0.001). Not surprisingly, a significant decrease in the predialysis serum concentration of the substance was obtained after changing treatment from cuprophan hemodialysis to hemodialysis with high-permeable membranes (delta beta 2M = -16.1 +/- 14.4 mg/L at month 6, p less than 0.01). These results suggest the possible long-term use of these membranes to reduce risk of dialysis-related amyloidosis.

[Subclinical neuropathies and paraproteinemias]. / Neuropatie subcliniche e paraproteinemie.

The relationship between monoclonal gammapathies and peripheral nerve involvement is well known. The pathogenesis of neuropathy has been ascribed to infiltrative, compressive, ischemic or haemorrhagic phenomena, to an amyloid storage or to antibody autoaggression toward neural antigens. Forty-five patients suffering from monoclonal gammapathy of uncertain significance (MGUS), multiple myeloma (MM), MG IgM, were submitted to a neurophysiological examination. 10 pts. were excluded because of neurotoxic drugs, diabetes or alcohol abuse. The investigation included SCV of median, ulnar, and sural n., MCV and F wave of peroneal n., H reflex, and computerized analysis of recruitment pattern. A subclinical neuropathy was found in 11 of 35 pts. (30%) without any neurological symptom. A CTS was found in 4 patients. The high rate of subclinical neuropathy in asymptomatic pts. is underlined by the Authors, while the presence of subclinical neuropathy in cases of MGUS needs further studies.