The use of antiferromagnetic materials in spintronic devices has been proposed as an attractive alternative to ferromagnets, but only a few suitable materials are known. Here, the authors synthesize a new antiferromagnet (AFM)—tetragonal epitaxial CuMnAs—and show that it is ideal for spintronic applications.

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Tetragonal phase of epitaxial room-temperature antiferromagnet CuMnAs

The dependence of exchange bias on antiferromagnet thickness has been measured in FeF 2 /Fe and MnF 2 /Fe bilayers. The two fluoride systems have identical crystal structures, similar lattice constants, but anisotropy fields that differ by a factor of 20. Hence, by comparing the antiferromagnetic layer thickness dependence of the exchange bias in the two systems we are able to directly establish the effect of the antiferromagnet anisotropy. We find that the critical antiferromagnet thickness for the onset of exchange biasing is an order of magnitude smaller for the more anisotropic fluoride, confirming the often-used assumption that the anisotropy dictates the critical thickness. By measuring the temperature dependence of the exchange bias and the structural morphology of the layers we are able to prove that the effects we observe are not due to the blocking-temperature thickness dependence or the onset of discontinuity in thin antiferromagnet lavers.

Effect of anisotropy on the critical antiferromagnet thickness in exchange-biased bilayers

c(2 x 2)CO ON Ni(100): Photoemission orientation determination

Hydrogen fuel receives worldwide attention for the zero emission and high energy density. Production of hydrogen by electrochemical water splitting requires efficient electrocatalysts to boost the hydrogen evolution reaction (HER). Transition metal phosphides are regarded as promising substitutes for precious metals as HER electrocatalysts. This review focuses on the recent progress with respect to the advantages, common synthetic approaches and enhancement strategies of Fe, Co and Ni-based phosphides, with important works in each section elaborately introduced for researchers in the relevant area. After the rational design and fabrication, Fe, Co and Ni-based phosphides can become highly efficient, durable and cost-effective electrocatalysts, and thereby exhibit a great potential for the scale-up production of hydrogen fuel.

A review of the electrocatalysts on hydrogen evolution reaction with an emphasis on Fe, Co and Ni-based phosphides

We report a comprehensive study of magnetic properties of Ni3TeO6. The system crystallizes in a noncentrosymmetric rhombohedral lattice, space group R3. There are three differently coordinated Ni atoms in the unit cell. Two of them form an almost planar honeycomb lattice, while the third one is placed between the layers. Magnetization and specific heat measurements revealed a single magnetic ordering at T-N = 52 K. Below TN the susceptibility with the magnetic field parallel to the c axis drops towards zero while the perpendicular susceptibility remains constant, a characteristic of antiferromagnetic materials. Neutron diffraction confirmed that the system is antiferromagnet below T-N with ferromagnetic ab planes stacked antiferromagnetically along the c axis. All Ni moments are in the S = 1 spin state and point along the c axis.

/pdf/ni3teo6-a-collinear-antiferromagnet-with-ferromagnetic-2s8ixbma6l.pdf

Ni3TeO6-a collinear antiferromagnet with ferromagnetic honeycomb planes

Susceptibility, resistivity and thermal expansion measurements have been performed on single crystals of FeP. The temperature ranges were 4.2 K-300 K, 15 K-300 K and 95 K-300 K respectively. The susceptibility measurements show a magnetic transition at 120 K, which is due to an antiferromagnetic ordering in the ab-plane. Above TN there is a considerable amount of anisotropy. The susceptibility curves representing the three principal directions have maxima around 220 K. The magnetic structure is interpreted in terms of a linear chain model. This interpretation of the experimental results is based on the theoretical work by Kallel et al. Resistivity measurements, carried out with the van der Pauw method, give an anisotropic resistivity tensor. The resistivity vs. temperature curves have points of inflexion at 115 K. The thermal expansion coefficient of the b-axis is much larger than the coefficients of the other axes.

Magnetic Susceptibility Resistivity and Thermal Expansion Measurements on FeP

SQUID magnetometer measurements of the magnetic susceptibility (χ|| and χ⊥) of MnF2 have been carried out in the temperature interval 4.2 to 300 K, with special emphasis paid to the region in the immediate vicinity of the Neel point. By combining our data with specific heat data from Teaney (Phys. Rev. Lett. 14, 898, 1965) we have checked the validity of Fisher's relation between the magnetic specific heat Cm and the magnetic parallel susceptibility χ||. Fisher's relation states: Cm/R K ∂/∂T (χ||T) where K is a factor of proportionality nearly independent of temperature. We find that Fisher's relation is well obeyed in the temperature interval: 2 × 10-4 < | T/TN - 1| < 6 × 10-2

http://iopscience.iop.org/article/10.1088/0031-8949/20/1/019/pdf

Critical Behaviour of the Magnetic Susceptibility of MnF2 Near the Néel Point

Crystalline anisotropy energy of uniaxial antiferromagnets evaluated from low field torque data

Magnetocrystalline anisotropy of MnF2 deduced from static torque

A magnetometer for measuring torques in the range 10-10 Nm -5·10-4 Nm (10-3 dyncm -5·103 dyncm) is described. Torque compensation is achieved by feedback from a photodetector into a PID regulator system which generates a current through a compensation coil located in the field of permanent magnets. Stability criteria for the regulator system are discussed. The apparatus permits continuous measurement of the torque as a function of angle with simultanuous registration of the data on x-y-recorder and on paper tape for computer analysis. Measurements can be made in the temperature range 4.2 K to 400 K.

Uno Gäfvert

Papers

Magnetic Susceptibility Resistivity and Thermal Expansion Measurements on FeP

Critical Behaviour of the Magnetic Susceptibility of MnF2 Near the Néel Point

Crystalline anisotropy energy of uniaxial antiferromagnets evaluated from low field torque data

Magnetocrystalline anisotropy of MnF2 deduced from static torque

A Torque Magnetometer with Proportional-Integrating-Differentiating (PID) Compensation