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A magnetic field driven quantum critical point (QCP) is studied experimentally in the Ce3Al magnetically anisotropic intermetallic compound, which shows both antiferromagnetic (AFM) ordering and heavy–fermion behavior. Measurements of the magnetic susceptibility, the magnetoresistance and the specific heat on a Ce3Al monocrystalline sample performed down to 0.35 K in magnetic fields up to 9 T demonstrate that the QCP is anisotropic regarding the orientation of the magnetic field relative to the magnetically easy direction. External magnetic field drives the AFM transition continuously toward zero temperature when applied in the (a, b) easy plane, reaching the QCP at the critical field B c a , b = 4.6 ± 0.4 T, where a quantum phase transition from the AFM to the paramagnetic state takes place. The magnetoresistance experiments below 1 K indicate that intermediate magnetic states may have formed near the QCP. For the field applied along the c hard direction, the QCP has not been observed within our experimental range of the magnetic field. The anisotropic, magnetic field driven QCP in the Ce3Al results from competition of the exchange interaction with the Zeeman interaction in the presence of a large magnetocrystalline anisotropy. The anisotropy of the QCP is a consequence of the fact that the magnetic anisotropy locks the magnetization into the easy plane and cannot be pulled out of the plane by the available laboratory field. Consequently, only the component of the magnetic field vector that lies in the easy plane participates in the QCP formation. In AFM systems with a large magnetic anisotropy, the magnetic field driven QCP is a continuous variable of the magnetic field vector orientation relative to the easy direction.

Iron and copper are immiscible elements, but can be combined in the presence of a third element such as aluminium or cerium. We varied the additions of immiscible Fe and Cu (ratio y) in the stoichiometric Al20.5Ce41.5(FeyCu1 − y)38 alloys in order to trace their impact on the structure, microstructure, thermal properties and magnetism. By powder X-ray diffraction (PXRD), we found that Fe-rich alloys (0.87 ≤ y ≤ 1) do not completely hinder crystallisation and yield nanocrystalline precipitates. Cu-rich alloys completely vitrify for 0 ≤ y ≤ 0.74 and exhibit a characteristic broad hump in PXRD patterns. DSC shows that Cu-rich alloys exhibit a noticeably lower crystallisation temperature Tx of about 510 K, liquidus temperature Tl at approximately 900 K and a more pronounced drop Δ of the heat flux at the glass transition temperature Tg. These criteria indicate that Cu-rich alloys are better glass formers. Transmission electron microscopy (TEM) shows that the specimens with y = 0 and y = 0.34 are composed of an amorphous matrix with minor impurities of CeO2 nanocrystals, which can only be observed via transmission electron microscopy. However, these nanocrystals do not interfere with the formation of the glassy phase and are therefore inert. Magnetic measurements show that Fe-rich alloys possess higher magnetisation at maximum field (Mmax H), peaking at 3.3 and 3 emu/g for y = 1 and y = 0.87, respectively. From ferromagnetism in the latter two alloys, the behaviour turns to paramagnetism for 0 ≤ y ≤ 0.74. Cryogenic measurements on SQUID show that the sample with y = 0 displays two different temperature regions at 2–50 K and 100–300 K. The first one exhibits nearly pure paramagnetic behaviour with Θ = − 0.7, while the second one shows a highly negative Weiss constant of Θ = − 80.6.

We report on the effect of loading factor and pressure on the density and the magnetic properties of Zn-bonded Nd–Fe–B magnets produced by pulsed-electric-current sintering (PECS). The idea behind this study is to fabricate bonded magnets with a metallic binder in order for the bonded magnet to operate at temperatures higher than 180 °C: the current upper-limit for polymer-bonded magnets. These composites are made of hard-magnetic powder in the form of melt-spun ribbons bonded with the low-melting-point metal Zn. The binder additions were varied from 10 to 30 wt%, and pressures of 50 and 500 MPa were applied. The high-pressure mode with 20 wt% Zn resulted in a 24% increase of J r , compared to the low-pressure mode. The magnetic measurements revealed a maximum remanence of 0.64 T for 10 wt% Zn, while the coercivity is largely unaffected by the processing conditions. The density of the composites was up to 7.0 g/cm 3 , corresponding to 94% of the theoretical density. Compared to commercial polymer-bonded magnets, the Zn-bonded counterparts exhibit a slightly lower J r , but the coercivity is retained. We show that there is a minor diffusion of Zn into the Nd–Fe–B, forming a 1 μm thin transition layer, but it does not harm the magnetic properties. These metal-bonded Nd–Fe–B magnets are ideal for use in high-temperature automotive applications like under-the-hood sensors and other magnet-based devices that are close to the engine.

The present work describes the formation of amorphous alloys in the (Al1−xCex)62Cu25Fe13 quaternary system (0 ≤ x ≤ 1). When the amount of Ce falls in the range 0.67 ≤ x ≤ 0.83, the alloys obtained exhibit a completely amorphous structure confirmed by powder X-ray diffraction. Otherwise, at compositions x = 0.5, 0.58, 0.92 and 1, a primary crystalline phase forms together with an amorphous matrix. The crystallisation temperature (Tx) decreases with increasing Ce content, varying from 593 K for x = 0.5–383 K for x = 1. Composition x = 0.75 is considered as the best glass former, exhibiting a large supercooled liquid region of 40 K width that precedes crystallisation. In order to form bulk amorphous alloys, ribbons with this later composition were consolidated into few millimetre thick discs using pulsed electric current sintering at different temperatures, yet preserving the amorphous structure. Meanwhile, increasing temperature above 483 K triggers crystallisation of a primary phase isostructural ...

We studied the effects of substituting gadolinium in the compound Cu5Gd with Ca by investigating the phase stability and crystal structure of the resulting new compounds. For rapidly quenched materials produced by melt spinning, the crystal structure was always hexagonal P6/mmm, irrespective of the Ca addition (x) in alloys with the formula Cu5Gd1-xCax, indicating good solid solubility under these conditions, which was additionally confirmed by Vegard’s law. Slower cooling upon arc-melting process caused the phase separation into Cu4Gd and CuCa. Using TEM, we investigated rapidly solidified ribbons of Cu5Gd0.5Ca0.5 and observed co-existence of Cu–Ca secondary phase with a matrix phase having the nominal stoichiometric composition. The oxygen level in this sample was found to be within 2–5 at. %, which was attributed to surface oxidation during or after TEM sample preparation. Upon hydrogenation, the crystal structure of all samples changed from hexagonal to cubic (F-43m), which is the thermodynamically stable polymorph of Cu5Gd compound. Strong catalytic activity of water formation from gaseous H2 and O2 was coincidentally discovered during dehydrogenation experiment, thus making this material as potential candidate for zero-platinum oxygen reduction catalyst.

We report on synthesis and characterization of a novel group of compounds based on copper, gadolinium, and calcium. Cu-Ca and Cu-Gd binaries were previously studied while Ca and Gd are known to be immiscible themselves. The effects of substituting Gd with Ca in Cu5Gd1-xCax compounds (0≤x≤1) were studied by investigating the phase stability and crystal structure of the resulting new compounds in five specimens with x = 0, 0.33, 0.50, 0.66, and 1, respectively. The samples produced by melt-spinning had hexagonal P6/mmm structure, irrespective of Ca amount (x), where lattice parameters varied with x linearly. This is an indication of good solid solubility under the preparation conditions. A slower cooling upon arc-melting caused the liquid phase separation into Cu4.5Gd and Cu-Ca compounds. Using TEM, rapidly solidified ribbons (Cu5Gd0.5Ca0.5) were investigated and the formation of a homogeneous ternary phase with a nearly nominal stoichiometric composition and minor amounts of Cu-Ca secondary phase was observed. Using DSC and HT XRD, we found that these systems are stable at least up to 400°C. Upon a 16-hour hydrogenation at 1 bar and 300°C, all specimens absorbed about 0.5 wt.% of hydrogen. This caused changes in structure with the formation of pure Cu and H2Gd1-xCax solid solution.