Room Temperature Ferromagnetic Mn:Ge(001)

Abstract

We report the synthesis of a room temperature ferromagnetic Mn-Ge system obtained by simple deposition of manganese on Ge(001), heated at relatively high temperature (starting with 250 °C). The samples were characterized by low energy electron diffraction (LEED), scanning tunneling microscopy (STM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), superconducting quantum interference device (SQUID), and magneto-optical Kerr effect (MOKE). Samples deposited at relatively elevated temperature (350 °C) exhibited the formation of ~5–8 nm diameter Mn5Ge3 and Mn11Ge8 agglomerates by HRTEM, while XPS identified at least two Mn-containing phases: the agglomerates, together with a Ge-rich MnGe~2.5 phase, or manganese diluted into the Ge(001) crystal. LEED revealed the persistence of long range order after a relatively high amount of Mn (100 nm) deposited on the single crystal substrate. STM probed the existence of dimer rows on the surface, slightly elongated as compared with Ge–Ge dimers on Ge(001). The films exhibited a clear ferromagnetism at room temperature, opening the possibility of forming a magnetic phase behind a nearly ideally terminated Ge surface, which could find applications in integration of magnetic functionalities on semiconductor bases. SQUID probed the co-existence of a superparamagnetic phase, with one phase which may be attributed to a diluted magnetic semiconductor. The hypothesis that the room temperature ferromagnetic phase might be the one with manganese diluted into the Ge crystal is formulated and discussed.

Magnetic properties of Mn doped crystalline and amorphous Ge thin films grown on Si (111)

“…The spin-orbit splitting energy ( ∆ so) value for both films is 11 eV. This energy splitting is lower than that of metallic Mn (11.4) [19]. The decrease of spin-orbit splitting energy indicates that the Mn detected in the films is probably in the cluster form.…”

“…The Mn 2p spectra of a-MnGe and c-MnGe taken after annealing process are shown in Figure 2 and display 2 spin-orbit doublets with lower and higher energies, which can be assigned to the binding energies of Mn 2p 1/2 and Mn 2p 3/2 , respectively. The first doublets at 638.8 and 649.8 eV and the second doublets at 639.9 and 650.9 eV are ascribed to metallic Mn and metallic manganese phases such as Mn 5 Ge 3 [19] and Mn 5 Ge 3−x Si x [20], respectively. It should be noted that the binding energies of Mn 2p related peaks in c-MnGe were negatively shifted compared to those of Mn 2p in a-MnGe, and the intensity of the higher energy component is stronger than that in a-MnGe.…”