We report HfCo7 nanoparticles with appreciable permanent-magnet properties (magnetocrystalline anisotropy K1 ≈ 10 Mergs/cm3, coercivity Hc ≈ 4.4 kOe, and magnetic polarization Js ≈ 10.9 kG at 300 K) deposited by a single-step cluster-deposition method. The direct crystalline-ordering of nanoparticles during the gas-aggregation process, without the requirement of a high-temperature thermal annealing, provides an unique opportunity to align their easy axes uniaxially by applying a magnetic field of about 5 kOe prior to deposition, and subsequently to fabricate exchange-coupled nanocomposites having Js as high as 16.6 kG by co-depositing soft magnetic Fe-Co. This study suggests HfCo7 as a promising rare-earth-free permanent-magnet alloy, which is important for mitigating the critical-materials aspects of rare-earth elements.
We report a facile synthesis of hard magnetic L10-FePtAu nanoparticles by coreduction of Fe(acac)3, Pt(acac)2 (acac = acetylacetonate), and gold acetate in oleylamine. In the current reaction condition, NP sizes are controlled to be 5.5 to 11.0 nm by changing the amount of Au doping. When the Au composition in the NPs is higher than 14%, the hard magnetic NPs are directly obtained without any annealing. The highest coercivity of 12.15 kOe at room temperature could be achieved for the NPs with 32% Au doping, which is much higher than the coercivities reported by the previous studies on solution-synthesized FePt nanoparticles. The reported one-pot synthesis of L10-FePtAu NPs may help to build superstrong magnets for magnetic or data-storage applications.
Nanostructured Mn y Ga ribbons with varying Mn concentrations including Mn 1.2 Ga, Mn 1.4 Ga, Mn 1.6 Ga, and Mn 1.9 Ga were prepared using arc-melting and melt-spinning followed by a heat treatment. Our experimental investigation of the nanostructured ribbons shows that the material with y ¼ 1.2, 1.4, and 1.6 prefers the tetragonal L1 0 structure and that with y ¼ 1.9 prefers the D0 22 structure. We have found a maximum saturation magnetization of 621 emu/cm 3 in Mn 1.2 Ga which decreases monotonically to 300 emu/cm 3 as y reaches 1.9. Although both the L1 0 -and D0 22 -Mn y Ga samples show a high Curie temperature (T c ) well above room temperature, the value of T c decreases almost linearly from 702 K for Mn 1.9 Ga to 551 K for Mn 1.2 Ga. All the ribbons are metallic between 2 K and 300 K but the Mn 1.2 Ga also shows a resistance minimum near 15 K. The observed magnetic properties of the Mn y Ga ribbons are consistent with the competing ferromagnetic coupling between Mn moments in the regular L1 0 -MnGa lattice sites and antiferromagnetic coupling with excess Mn moments occupying Ga sites. V C 2013 AIP Publishing LLC. [http://dx
The structural, magnetic, and electron transport properties of Mn55−xFexBi45 (x = 0, 2, 4, 5, 8, 11, 13, 16) films prepared by multilayer deposition and annealing using e-beam evaporation have been investigated. Fe doping has produced a significant change in the magnetic properties of the samples including the decrease in saturation magnetization and magnetocrystalline anisotropy and increase in coercivity. Although the magnetization shows a smooth decrease with increasing Fe concentration, the coercivity jumps abruptly from 8.5 kOe to 22 kOe as Fe content changes from 4% to 5%, but the change in coercivity is small as the concentration goes beyond 5%. The temperature dependence of resistivity shows that the samples with low Fe concentration (≤4%) are metallic, but the resistivity increases unexpectedly as the concentration reaches 5%, where the resistance increases with decreasing temperature below 300 K. First-principle calculations suggest that the observed magnetic properties can be understood as the consequences of competing ferromagnetic and antiferromagnetic exchange interactions between the interstitial atom and the rest of the MnBi lattice.
The growth of new magnetic materials on suitable insulating substrates is an important part of the development of spin-electronics devices for memory or information processing. Epitaxial thin films of Mn2PtSn were grown on a MgO [001] substrate by magnetron co-sputtering of the constituents. Structural, magnetic, and electron-transport properties were investigated. The epitaxial Mn2PtSn film has an inverse tetragonal structure with the c-axis aligned in the plane of the MgO substrate. The lattice constants determined using XRD and TEM analysis are c = 6.124 Å and a = b = 4.505 Å. The orientation of Mn2PtSn c-axis which is 45° away from the a-axis of MgO has resulted in a small lattice mismatch of about 2.8%. The measured saturation magnetization is 5.3 μB/f.u., which is smaller than the first-principles calculated value of 6.4 μB/f.u. for ferromagnetic spin arrangement. Magnetization measurements determined the bulk magnetocrystalline anisotropy constant Kv of about 11.3 Merg/cm3 (1.13 MJ/m3). The electron-transport behavior is similar to that of normal magnetic metals. These results indicate that Mn2PtSn may have promising applications in spintronic devices.
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