A successive multi-phase transitions in polycrystalline BaFe2As2: Emergence of C4 phase

We report magnetization and resistivity studies on polycrystalline BaFe2As2 prepared by solid-state reaction, in the temperature range of 5–350 K, upto the field of 9 T. Low-field susceptibility exhibits multi-phase transitions with two new magnetic phase transitions beside the well-known transition at [Formula: see text] K from paramagnetic/antiferromagnetic-tetragonal/orthorhombic transitions. The phase at [Formula: see text] K is attributed to the phase transition from antiferromagnetic-orthorhombic (C2-phase) to antiferromagnetic-tetragonal phase (C4-phase), while the phase transition at higher temperatures remains unsolved. Making an analogy to the antiferromagnetic nanosized particles, we suggest that BaFe2As2 consists of smaller but similar nanosized clusters. We have analyzed the magnetization data using the modified Langevin function on the basis of thermally activated induced uncompensated spins (thermoinduced moments). The nanosized clustering in this compound is evidenced by the exchange bias and coercivity stemming from the exchange coupling interactions between weak ferromagnetic bulk magnetization in clusters and spin-glass-like phase interface layers surrounding the clusters. We also observe that annealing enhances the superconductivity, similar to the effect of pressure on the superconductivity. We find that an exponential term well describes the resistivity of this compound due to magnon-assisted interband electron–phonon scattering between the bands with [Formula: see text] and [Formula: see text] orbitals forming two-hole pockets around the zone center and one electron pocket around the zone corner. We have also obtained the Kadowaki–Woods ratio ([Formula: see text] cm (K mol/mJ)[Formula: see text] and the Sommerfeld–Wilson ratio ([Formula: see text]) for BaFe2As2, both ratios are much larger than those ([Formula: see text]/[Formula: see text] cm (K mol/mJ)2, [Formula: see text]) for Kondo lattice systems, indicating the existence of a weak ferromagnetic correlation between Fe moments. It appears that magnon-mediated pairing is responsible for superconductivity. Finally, we observe zero resistance at [Formula: see text] K in amorphous BaFe2As2, which gives a new insight into the superconductivity under very high pressure.

Soft Ferromagnetic Bulk Metallic Glass with Potential Self-Healing Ability

A new concept of soft ferromagnetic bulk metallic glass (BMG) with self-healing ability is proposed. The specific [Fe36Co36B19.2Si4.8Nb4]100−x(Ga)x (x = 0, 0.5, 1 and1.5) BMGs prepared by copper mold casting were investigated as a function of Ga content. The Ga-containing BMGs still hold soft magnetic properties and exhibit large plastic strain of 1.53% in compression. Local melting during shearing produces molten droplets of several µm size throughout the fracture surface. This concept of local melting during shearing can be utilized to produce BMGs with self-healing ability. The molten regions play a vital role in deflecting shear transformation zones, thereby enhancing the mechanical properties.

Current-driven magnetization switching in ferromagnetic bulk Rashba semiconductor (Ge,Mn)Te

Multiferroic materials with both ferroelectric and ferromagnetic orders provide a promising arena for the electrical manipulation of magnetization through the mutual correlation between those ferroic orders. Such a concept of multiferroics may expand to semiconductor with both broken symmetries of spatial inversion and time reversal, that is, polar ferromagnetic semiconductors. Here, we report the observation of current-driven magnetization switching in one such example, (Ge,Mn)Te thin films. The ferromagnetism caused by Mn doping opens an exchange gap in original massless Dirac band of the polar semiconductor GeTe with Rashba-type spin-split bands. The anomalous Hall conductivity is enhanced with increasing hole carrier density, indicating that the contribution of the Berry phase is maximized as the Fermi level approaches the exchange gap. By means of pulse-current injection, the electrical switching of the magnetization is observed in the (Ge,Mn)Te thin films as thick as 200 nm, pointing to the Rashba-Edelstein effect of bulk origin. The efficiency of this effect strongly depends on the Fermi-level position owing to the efficient spin accumulation at around the gap. The magnetic bulk Rashba system will be a promising platform for exploring the functional correlations among electric polarization, magnetization, and current.

Establishing the Glass Forming Ability of Ferromagnetic Bulk Amorphous Alloys Using a Mathematical Model Based on the Chemical Composition

This paper presents a mathematical model that describes the influence of the chemical composition on the glass forming ability of ferromagnetic alloys. Glass forming ability is given by the difference between the glass transition temperature and the primary crystallization temperature of the alloy. The glass forming ability is better as long this difference has a higher value. These temperatures were determined using differential thermal analysis.

The Effect of Co Addition on Glassy Forming Ability and Soft Magnetic Properties of Fe-Si-B-P Bulk Metallic Glass

We Successfully Prepared the Rod Glassy Samples of (Fe1-xCox)76Si9B10P5 (x = 0~0.4) Bulk Metallic Glass (BMG) with the Diameters up to 3.0 mm by Substituting Fe for a Small Amount of Co Element. A Certain Amount of Co Substitution for Fe Contributes to the Increase of the Glass-Forming Ability (GFA) while Maintaining Good Mechanical Properties (the Fracture Strength up to 3700 MPa). This Co-Added Ferromagnetic Bulk Glassy Alloy System Also Exhibits a Higher Saturation Magnetization of 1.49 T and Lower Coercive Force (Hc, 1.2 A/m). The Fe-Based BMGs with Alloying a Small Amount of Co Element Demonstrate Excellent Combination of High GFA, Good Soft-Magnetic Properties as Well as High Strength.

EFFECT OF COPPER ADDITIVES ON IRREVERSIBLE MELTING IN [{(Fe0.5Co0.5)0.75B0.2Si0.05}96Nb4]100-xCux, x ≤ 3, ALLOYS

Iron and cobalt based ferromagnetic bulk amorphous alloys have received considerable interest nowadays in view of their useful properties for wide spread applications in magnet technology, shape memory alloys, high frequency communications at low power loss, and other devices. In this purview, here we report synthesis and thermal properties of bulk amorphous alloys [{( Fe 0.5 Co 0.5)0.75 B 0.2 Si 0.05}96 Nb 4]100-x Cu x (x = 0, 1, 2, and 3). A copper mould casting of molten alloy was used to obtain a vitrified alloy in form of thin rods (1–2 mm diameter). Amorphous structure retains at a cooling rate as low as 100 K/s in argon atmosphere. Heat out-put measured in terms of a differential scanning calorimetric signal during heating and cooling cycles of these alloys demonstrate irreversibility in a compositional dependent melting point, which follows the glass transition temperature and successive crystallization. The irreversibility persists in this specific example of the bulk amorphous alloys even on sufficiently slow heating or cooling rates such as 0.33 K/s in argon. The copper inclusion tailors the melting point, the enthalpy of the fusion, and other thermodynamic parameters. Results are analyzed in corroboration to the magnetic properties.