Effect of processing parameters on the structure and magnetic properties of Nd60Fe30Al10 alloy

Although rapidly solidified Nd–Fe–Al alloys exhibit hard magnetic properties they so far have not found any practical application, however, their study has great scientific meaning. Investigations of the Nd–Fe–Al alloys enable one to evaluate the effect of magnetic interactions, between nanoscale precipitates, having different structure and properties, on the macroscopically observed phenomena. The evolution of microstructure in the course of annealing is generally unclear. Most of the reported data were obtained for different materials, using various processing methods, which makes their comparison difficult. It was shown that different fabrication methods (melt spinning, suction casting) generate different properties. On the other hand, for the particular processing method the structure and magnetic properties are highly affected by the processing variables.

In this study the samples fabricated by two methods were compared. Melt spinning, with the roll speed 5–30 m/s, and casting into moulds having bore diameters 1, 3, 6 and 12 mm were used. The alloy composition was kept constant Nd₆₀Fe₃₀Al₁₀. Strong dependence of the magnetic properties on quenching rate was proved. Application of the appropriate processing variables for both the methods (roll speed or rode diameter) enables one to obtain comparable quenching rates and thus overall similar magnetic properties. However, for the cylindrical specimens different cooling rates for the surface and core produces a structural gradient, which leads to variation of the magnetic properties on the sample cross-section. The structural and property gradients were evaluated using SEM and magnetic measurements, respectively.     

Permanent magnet assembly producing a strong tilted homogeneous magnetic field: towards magic angle field spinning NMR and MRI

We introduce a cylindrical permanent magnet design that generates a homogeneous and strong magnetic field having an arbitrary inclination with respect to the axis of the cylinder. The analytical theory of 3 D magnetostatics has been applied to this problem, and a hybrid magnet structure has been designed. This structure contains two magnets producing a longitudinal and transverse component for the magnetic field, whose amplitudes and homogeneities can be fully controlled by design. A simple prototype has been constructed using inexpensive small cube magnets, and its magnetic field has been mapped using Hall and NMR probe sensors. This magnet can, in principle, be used for magic angle field spinning NMR and MRI experiments allowing for metabolic chemical shift profiling in small living animals.     

Magnetostructural Correlations in Tetrairon(III) Single‐Molecule Magnets

Tunable single‐molecule magnets : The spin‐level landscape in a series of Fe^III₄ single‐molecule magnets with propeller‐like structure was analyzed by means of high‐frequency EPR spectroscopy. The zero‐field splitting parameter D of the ground S=5 spin state correlates strongly with the pitch of the propeller γ (see picture), and thus provides a simple link between molecular structure and magnetic behavior.

     

上海光源真空波荡器Sm2Co17永磁铁的实验研究

对国产Sm2Co17永磁铁(XG30/20)研制工艺进行了改进,对三种成型-烧结设计所得到的永磁铁样品(65 mm27 mm7.2 mm)进行了测试与分析,结果表明,磁性能有所改善,磁矩一致性和稳定性良好,获得了国产真空波荡器Sm2Co17永磁铁的优化成型-烧结设计和磁场分布规律数据,对永磁铁实验研究结果原理进行了解释。     

高温超导磁体临界电流的磁矢量分析法及其验证

临界电流是高温超导磁体的关键参数,文中提出了一种名为"磁矢量分析法"的高温超导临界电流计算方法。这种方法以高温超导带材性能测试结果为依据,以有限元仿真软件为手段,通过对计算高温超导磁体内部电磁感应强度矢量的分布,采用插值运算来确定高温超导磁体的临界电流。通过在77K温度下进行1:1的磁体实验,磁矢量分析法的可行性得到了验证。     

Enhancing the blocking temperature in single-molecule magnets by incorporating 3d-5d exchange interactions

We report the first single-molecule magnet (SMM) to incorporate the [Os(CN)(6)](3-) moiety. The compound (1) has a trimeric, cyanide-bridged Mn(III)-Os(III)-Mn(III) skeleton in which Mn(III) designates a [Mn(5-Brsalen)(MeOH)](+) unit (5-Brsalen=N,N'-ethylenebis(5-bromosalicylideneiminato)). X-ray crystallographic experiments reveal that 1 is isostructural with the Mn(III)-Fe(III)-Mn(III) analogue (2). Both compounds exhibit a frequency-dependent out-of-phase χ'(T) alternating current (ac) susceptibility signal that is suggestive of SMM behaviour. From the Arrhenius expression, the effective barrier for 1 is found to be Δ(eff)/k(B)=19 K (τ(0)=5.0×10(-7) s; k(B)=Boltzmann constant), whereas only the onset (1.5 kHz, 1.8 K) of χ'(T) is observed for 2, thus indicating a higher blocking temperature for 1. The strong spin-orbit coupling present in Os(III) isolates the E'(1g(1/2))(O(h)*) Kramers doublet that exhibits orbital contributions to the single-ion anisotropy. Magnetic susceptibility and inelastic neutron-scattering measurements reveal that substitution of [Fe(CN)(6)](3-) by the [Os(CN)(6)](3-) anion results in larger ferromagnetic, anisotropic exchange interactions going from quasi-Ising exchange interactions in 2 to pure Ising exchange for 1 with J(parallel)(MnOs)=-30.6 cm(-1). The combination of diffuse magnetic orbitals and the Ising-type exchange interaction effectively contributes to a higher blocking temperature. This result is in accordance with theoretical predictions and paves the way for the design of a new generation of SMMs with enhanced SMM properties.