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Register a new userTunability of Room Temperature Ferromagnetism in Spintronic Semiconductors through Non-magnetic Atoms
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The implementation and control of room temperature ferromagnetism (RTFM) by adding magnetic atoms to a semiconductors lattice has been one of the most important problems in solid state state physics in the last decade. Herein we report for the first time, to our knowledge, on the mechanism that allows RTFM to be tuned by the inclusion of emph{non-magnetic} aluminum in nickel ferrite. This material, NiFe$_{2-x}$Al$_x$O$_4$ (x=0, 0.5, 1.5), has already shown much promise for magnetic semiconductor technologies, and we are able to add to its versatility technological viability with our results. The site occupancies and valencies of Fe atoms (Fe$^{3+}$ T$_d$, Fe$^{2+}$ O$_h$, and Fe$^{3+}$ O$_h$) can be methodically controlled by including aluminum. Using the fact that aluminum strongly prefers a 3+ octahedral environment, we can selectively fill iron sites with aluminum atoms, and hence specifically tune the magnetic contributions for each of the iron sites, and therefore the bulk material as well. Interestingly, the influence of the aluminum is weak on the electronic structure (supplemental material), allowing one to retain the desirable electronic properties while achieving desirable magnetic properties.
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Nanoparticles of superconducting YBa2Cu3O7-delta (YBCO) (Tc = 91 K) exhibit ferromagnetism at room temperature while the bulk YBCO, obtained by heating the nanoparticles at high temperature (940 degree C), shows a linear magnetization curve. Across the superconducting transition temperature, the magnetization curve changes from that of a soft ferromagnet to a superconductor. Furthermore, our experiments reveal that not only nanoparticles of metal oxides but also metal nitrides such as NbN (Tc = 6 - 12 K) and delta-MoN (Tc ~ 6 K) exhibit room-temperature ferromagnetism.
We report the observation of large magnetocaloric effect near room temperature in antipervoskite SnCMn3. The maximal magnetic entropy change at the first-order ferrimagnetic-paramagnetic transition temperature (TC 279 K) is about 80.69mJ/cm3 K and 133mJ/cm3 K under the magnetic field of 20 kOe and 48 kOe, respectively. These values are close to those of typical magnetocaloric materials. The large magnetocaloric effect is associated with the sharp change of lattice, resistivity and magnetization in the vicinity of TC. Through the measurements of Seebeck coefficient and normal Hall effect, the title system is found to undergo a reconstruction of electronic structure at TC. Considering its low-cost and innocuous raw materials, Mn-based antiperovskite compounds are suggested to be appropriate for pursuing new materials with larger magnetocaloric effect.
A complex interplay of different energy scales involving Coulomb repulsion, spin-orbit coupling and Hunds coupling energy in two-dimensional (2D) van der Waals (vdW) material produces novel emerging physical state. For instance, ferromagnetism in vdW charge transfer insulator CrGeTe$_3$, that provides a promising platform to simultaneously manipulate the magnetic and electrical properties for potential device implementation using few layers thick materials. Here, we show a continuous tuning of magnetic and electrical properties of CrGeTe$_3$ single crystal using pressure. With application of pressure, CrGeTe$_3$ transforms from a FM insulator with Curie temperature, $T_{rm{C}} sim $ 66 K at ambient condition to a correlated 2D Fermi metal with $T_{rm{C}}$ exceeding $sim$ 250 K. Notably, absence of an accompanying structural distortion across the insulator-metal transition (IMT) suggests that the pressure induced modification of electronic ground states are driven by electronic correlation furnishing a rare example of bandwidth-controlled IMT in a vdW material.
In a recent Letter, Berciu and Bhatt have presented a mean-field theory of ferromagnetism in III-V semiconductors doped with manganese, starting from an impurity band model. We show that this approach gives an unphysically broad impurity band and is thus not appropriate for (Ga,Mn)As containing 1-5% Mn. We also point out a microscopically unmotivated sign change in the overlap integrals in the Letter. Without this sign change, stable ferromagnetism is not obtained.
We investigate the magnetocaloric effect (MCE), relative cooling power (RCP) and crystalline structure in Sb substituted CrTe_{1-x}Sb_{x} (0 leq x leq 0.2) alloy. The Rietveld refinement of the XRD pattern of CrTe1-xSbx showed the emerging of pure hexagonal NiAs structure with P63/mmc (194) space group with increasing Sb substitution. We detect a slight increase in the basal plane a-lattice parameter, with a much larger reduction in the c-axis. Magnetic isotherms were measured in the temperature range of 50-400K. The results revealed an increase in the maximum entropy change |S_{M}(T,H)| with Sb-substitutions in the temperature range (~285-325K). Moreover, The RCP values increased by about 33% with 20% Sb substitutions. These findings suggest that CrTe_{1-x}Sb_{x} alloys can be used in room temperature magnetic cooling at fraction of the coast of pure Gd element the porotype magnetic material for magnetic refrigeration.
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