Free-Standing and Single-Crystalline Fe_1–<i>x</i>Mn_<i>x</i>Si Nanowires with Room-Temperature Ferromagnetism and Excellent Magnetic Response

High-aspect-ratio Fe_1–xMn_<i>x</i>Si nanowires with room-temperature ferromagnetism were synthesized by a chemical vapor deposition (CVD) method in one step. This is the first report of ternary silicide nanowires using magnetic Mn ions to partially replace metal sites in the host matrix. Here we report the excellent magnetic characteristics of Fe_1‑<i>x</i>Mn_<i>x</i>Si nanowires, which exhibit strong ferromagnetism at room temperature and high magnetoresistance (MR) variation. As-synthesized Fe_1–<i>x</i>Mn_<i>x</i>Si nanowires show a hyperbranched morphology and a spin-disorder behavior. The strong spin interaction in Fe_1‑<i>x</i>Mn_<i>x</i>Si nanowires, induced by the substitution of Fe sublattices for magnetic Mn ions, was revealed in the hysteresis loops. The magnetization versus magnetic field (<b>M</b>–<b>H</b>) curves of Fe_1–<i>x</i>Mn_<i>x</i>Si nanowires are much less sensitive to the temperature variation from 10 to 300 K than those of FeSi nanowires. Remarkably, the excellent MR performance, −41.6% at 25 K with a magnetic field of 9 T, was demonstrated in an individual Fe_0.88Mn_0.12Si nanowire

Ferromagnetic Germanide in Ge Nanowire Transistors for Spintronics Application

To explore spintronics applications for Ge nanowire heterostructures formed by thermal annealing, it is critical to develop a ferromagnetic germanide with high Curie temperature and take advantage of the high-quality interface between Ge and the formed ferromagnetic germanide. In this work, we report, for the first time, the formation and characterization of Mn₅Ge₃/Ge/Mn₅Ge₃ nanowire transistors, in which the room-temperature ferromagnetic germanide was found through the solid-state reaction between a single-crystalline Ge nanowire and Mn contact pads upon thermal annealing. The atomically clean interface between Mn₅Ge₃ and Ge with a relatively small lattice mismatch of 10.6% indicates that Mn₅Ge₃ is a high-quality ferromagnetic contact to Ge. Temperature-dependent <i>I</i>–<i>V</i> measurements on the Mn₅Ge₃/Ge/Mn₅Ge₃ nanowire heterostructure reveal a Schottky barrier height of 0.25 eV for the Mn₅Ge₃ contact to <i>p</i>-type Ge. The Ge nanowire field-effect transistors built on the Mn₅Ge₃/Ge/Mn₅Ge₃ heterostructure exhibit a high-performance <i>p</i>-type behavior with a current on/off ratio close to 10⁵, and a hole mobility of 150–200 cm²/(V s). Temperature-dependent resistance of a fully germanided Mn₅Ge₃ nanowire shows a clear transition behavior near the Curie temperature of Mn₅Ge₃ at about 300 K. Our findings of the high-quality room-temperature ferromagnetic Mn₅Ge₃ contact represent a promising step toward electrical spin injection into Ge nanowires and thus the realization of high-efficiency spintronic devices for room-temperature applications

Electrical Probing of Magnetic Phase Transition and Domain Wall Motion in Single-Crystalline Mn₅Ge₃ Nanowire

In this Letter, the magnetic phase transition and domain wall motion in a single-crystalline Mn₅Ge₃ nanowire were investigated by temperature-dependent magneto-transport measurements. The ferromagnetic Mn₅Ge₃ nanowire was fabricated by fully germaniding a single-crystalline Ge nanowire through the solid-state reaction with Mn contacts upon thermal annealing at 450 °C. Temperature-dependent four-probe resistance measurements on the Mn₅Ge₃ nanowire showed a clear slope change near 300 K accompanied by a magnetic phase transition from ferromagnetism to paramagnetism. The transition temperature was able to be controlled by both axial and radial magnetic fields as the external magnetic field helped maintain the magnetization aligned in the Mn₅Ge₃ nanowire. Near the magnetic phase transition, the critical behavior in the 1D system was characterized by a power-law relation with a critical exponent of α = 0.07 ± 0.01. Besides, another interesting feature was revealed as a cusp at about 67 K in the first-order derivative of the nanowire resistance, which was attributed to a possible magnetic transition between two noncollinear and collinear ferromagnetic states in the Mn₅Ge₃ lattice. Furthermore, temperature-dependent magneto-transport measurements demonstrated a hysteretic, symmetric, and stepwise axial magnetoresistance of the Mn₅Ge₃ nanowire. The interesting features of abrupt jumps indicated the presence of multiple domain walls in the Mn₅Ge₃ nanowire and the annihilation of domain walls driven by the magnetic field. The Kurkijärvi model was used to describe the domain wall depinning as thermally assisted escape from a single energy barrier, and the fitting on the temperature-dependent depinning magnetic fields yielded an energy barrier of 0.166 eV