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Amorphous MoSe2 has been fabricated hydrothermally, and the degree of amorphousness was tuned by post-annealing procedures. Large room temperature ferromagnetism (RTFM) has been achieved for the amorphous MoSe2 which weakens during crystallization and phase transition from the 1T to the 2H structure. Theoretical calculations indicate that the amorphous MoSe2 exhibits higher magnetization compared with the crystalline 1T and 2H phases and that the magnetization mainly originates from the d orbitals of Mo atoms. This study provides insights into the RTFM for the amorphous transition metal dichalcogenides (TMDs) and provides amorphousness as a new option to tailor the magnetization of the TMDs for future spintronic applications.

TiO2 films have been grown on Si(100) substrates via pulsed laser deposition. Amorphousness has been achieved for films

The unitary deformation of single-phase ferromagnets by a magnetic field, i.e., either positive or negative linear magnetostriction, allows only monotonous control. Here we report a proof-of-principle ferromagnetic composite Fe73Ga27, for which the magnetostriction sign changes from positive to negative by increasing the magnetic field strength. Based on the transformation from body-centered-cubic (BCC) to face-centered-cubic (FCC) phases in this binary system, Fe73Ga27 composite is prepared by aging the BCC averaged precursor for 3 days at 803 K. Magnetic measurements indicate that the BCC phase exhibits smaller magnetocrystalline anisotropy constant than the FCC phase. The offset effect between BCC and FCC phases produces positive net magnetostriction at low magnetic fields but negative net magnetostriction at high magnetic fields. By tuning the field strength, such composites can mediate compressive and tensile strains to other functional materials, e.g., piezoelectric material or optic-fibers, which is beneficial to design multifunctional devices.

Defects-induced local symmetry breaking has led to unusual properties in nonferromagnetic ferroelastic materials upon suppressing their martensitic transformation. Thus, it is of interest to discover additional properties by local symmetry breaking in one important class of the ferroelastic materials, i.e., the ferromagnetic shape memory alloys. In this letter, it is found that local symmetry breaking including both tetragonal nano-inclusions and anti-phase boundaries (APBs), suppresses martensitic transformation of a body-centered-cubic Fe50Mn23Ga27 alloy, however, does not affect the magnetic ordering. Large electrical resistivity is retained to the low temperature ferromagnetic state, behaving like a half-metal ferromagnet. Lower ordering degree at APBs and local stress fields generated by the lattice expansion of tetragonal nanoparticles hinder the formation of long-range-ordered martensites. The half-metal-like conducting behavior upon suppressing martensitic transformation extends the regime of ferromagnetic shape memory materials and may lead to potential applications in spintronic devices.

Soluting rare earth atoms Tb or Dy into body centered cubic (BCC) Fe-Ga through rapid cooling significantly enhances the magnetostriction due to strong localized magnetocrystalline anisotropy. Origin of the local strong anisotropy, however, awaits comprehensive microstructural investigation. In this letter, formation of tetragonal nanoparticles with c/a ∼ 0.979 has been found in the giant magnetostrictive ribbons Fe82.89Ga16.88Tb0.23 due to local symmetry breaking of the BCC lattice using high resolution transmission electronic microscopy. First principal calculations suggest that random replacement of Tb atoms for Fe or Ga in the ordered DO3 superlattice is beneficial in the formation of such tetragonal symmetry. Exchange couplings between the nearest Tb-Fe or Tb-Tb pairs of the tetragonal nanoparticles might generate strong localized magnetocrystalline anisotropy, leading to extraordinary magnetostriction enhancement.

The recently reported morphotropic phase boundary (MPB) in a number of giant magnetostrictive materials (GMMs) has drawn considerable interest to the local symmetry/structure near MPB region of these materials. In this letter, by in-situ X-ray diffraction and AC magnetic susceptibility measurements, we show that Tb0.3Dy0.7Fe2, the typical composition of Terfenol-D GMMs, has coexistence of rhombohedral and tetragonal phases over a wide temperature range in the vicinity of MPB. High resolution transmission electron microscopy provides direct evidence for local rhombohedral symmetry of the ferromagnetic phase and reveals regular-shaped nanoscale domains below 10 nm. The nano-sized structural/magnetic domains are hierarchically inside a single micron-sized stripe-like domain with the same average magnetization direction. Such domain structures are consistent with the low magnetocrystalline anisotropy and easy magnetic/structural domain switching under magnetic field, thus generating large magnetostriction at low field.

The present work investigates quantitatively the effect of induced anisotropy axis on magnetostriction of Terfenol-D, exploring a possible method of tailoring flexibly magnetostriction for a particular purpose. It is found that the induced anisotropy axis shows significant effect on the initial domain state, magnetization process, and thus the magnetostriction. Magnetostriction behaviors for a specific induced anisotropy axis are discussed and compared with the experimental observations. The critical case for the expected 90° domain alignments has been also analyzed quantitatively. Diagrams of domain state evolutions are established, shining some light on understanding magnetostriction tunability and developing magnetostrictive material.

We report a systematic study of the crystallinity dependence of room-temperature ferromagnetism (RTFM) in pure MgO thin films prepared by pulsed laser deposition. A sequential transition from ferromagnetism to diamagnetism as a function of deposition temperature is observed. All the samples deposited from room temperature (RT) to 200 °C show clear RTFM, and the magnetization decreases monotonically with the increase of the substrate temperature, whereas the MgO film grown at 300 °C shows diamagnetism behavior like bulk MgO sample. The maximum saturation magnetization of 8 emu/cm3 is obtained for the MgO film deposited at RT, which degrades dramatically after crystallization under the annealing in both vacuum and air atmosphere. Further photoluminescence and X-ray photoelectron spectroscopies reveal that the ferromagnetism in the MgO thin films is correlated directly with the Mg vacancies.

We investigated the correlation between magnetization and oxygen vacancies in Zn0.95Co0.05O nanoparticles. Enhanced magnetizations were found in SiO2 nanopowders and carbon nanotubes (CNTS) treated Zn0.95Co0.05O, which are attributed to minimizing nanoparticle size and increasing oxygen vacancy concentration. After oxygen annealing, the magnetization of both non-treated Zn0.95Co0.05O and CNTS treated Zn0.95Co0.05O decreased sharply with the filling of the oxygen vacancies, while the SiO2 treated Zn0.95Co0.05O was influenced little as the amorphous SiO2 shell prevents the diffusion of oxygen into magnetic particles. It demonstrated that the ferromagnetism comes from the interfacial oxygen deficiency and is tunable by changing the oxygen vacancies.

The transport properties of graphene strips under tensile strain have been theoretically investigated. For the armchair-edge graphene nanoribbons (GNRs) with width N=3m−1, the additional negative differential resistance (NDR) undergoes a process from occurring to enhancement and then disappearance with increasing tensile strain. The changes in the additional NDR may be originated from the suppression of strain-mediated channel states for the variations in degenerate energy bands near Fermi level. The strain-induced NDR behaviors of the GNRs present the possibility of the potential applications in electromechanical nanodevices such as stress-controlled Goto pair for digital signal restoration.

The effect of Na concentration on the room-temperature ferromagnetism in Na and Co codoped ZnO diluted magnetic semiconductor (DMSs) was investigated. The ferromagnetic state was found to be stable below 5% doping of Na due to the exchange interaction via electron trapped oxygen vacancies (F-center) coupled with the magnetic Co ions. With large Na doping of up to 10%, a sharp reduction in the magnetization was observed, showing that the oxygen vacancy mediated antiferromagnetic state becomes predominant. The observed correlation between the Na concentration, the carrier concentration, and the magnetization demonstrated the effect of the defect in controlling the ferromagnetism in the ZnO-based DMS system.

Magnetic heat treatment has been carried out on a giant magnetostrictive alloy Tb0.36Dy0.64(Fe0.85Co0.15)2 with ⟨110⟩ crystal orientation. A dramatic improvement in magnetostriction along and perpendicular to the crystal axis (defined as λ‖ and λ⊥, respectively) occurs when cooling the sample through the Curie temperature TC under 240kA∕m applied perpendicular to its axis. When the applied annealing field was parallel to the crystal axis, the magnetostrictive behavior becomes “anomalous;” negative λ‖ and positive λ⊥ are obtained in low fields, accompanied with relatively low values in high fields. A single-{111}-twin model has been suggested to explain such differential magnetostrictive response.