Magnetic and structural properties ofGexMn1−xfilms: Precipitation of intermetallic nanomagnets

Abstract

We present a comprehensive study relating the nanostructure of Ge0.95Mn0.05 films to their magnetic properties. The formation of ferromagnetic nanometer sized inclusions in a defect free Ge matrix fabricated by low temperature molecular beam epitaxy is observed down to substrate temperatures TS as low as 70 • C. A combined transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) analysis of the films identifies the inclusions as precipitates of the ferromagnetic compound Mn5Ge3. The volume and amount of these precipitates decreases with decreasing TS. Magnetometry of the films containing precipitates reveals distinct temperature ranges: Between the characteristic ferromagnetic transition temperature of Mn5Ge3 at approximately room temperature and a lower, TS dependent blocking temperature TB the magnetic properties are dominated by superparamagnetism of the Mn5Ge3 precipitates. Below TB, the magnetic signature of ferromagnetic precipitates with blocked magnetic moments is observed. At the lowest temperatures, the films show features characteristic for a metastable state.

Tadpole shaped Ge0.96Mn0.04 magnetic semiconductors grown on Si

“…24 however, showed extensive experimental evidence that the GeMn exhibits a spin-glasslike behavior with two transition temperatures T f = 12 K and T b = 250 K. Their origins were attributed to the blocking or freezing transitions of two different kinds of superparamagnetic precipitates. Similarly, Ahlers et al 15 provided a detailed analysis on magnetic behaviors of the Mn 5 Ge 3 precipitates and lattice-coherent nanoclusters, which explained the blocking temperatures at 250 and 12 K, respectively. Likewise, we also observed two transition temperatures at T b1 ϳ 22 K ͑nanoclusters͒ and T b2 ϳ 250 K ͑Mn 5 Ge 3 ͒ as shown in the ZFC process ͓Fig.…”

“…3 When 250 K Ͻ T Ͻ 300 K, the precipitates are expected to react freely on an externally applied magnetic field like a superparamagnet. 15 So this temperature region corresponds to a superparamagnetic regime. ͑c͒ The ZFC curve shows another T b of ϳ22 K ͑T b1 ϳ 22 K͒.…”

Diluted manganese on the bond-centered site in germanium

“…However, the origin of ferromagnetism in this system, grown with molecular beam epitaxy ͑MBE͒ or by Mn implantation, is not yet fully understood and has been related to Mn-rich precipitates, such as Mn 5 Ge 3 and Mn 11 Ge 8 , as well as to magnetic coupling between diluted Mn impurities. [3][4][5][6] The ͑ferro-͒ magnetic behavior of diluted Mn atoms is expected to depend on their lattice site, which makes this property crucial for a correct understanding of magnetism in this system.…”

Comparison of the magnetic properties of GeMn thin films through Mn L-edge x-ray absorption

“…4 Increasing the fabrication temperature beyond 60°C additionally leads to the precipitation of nanometer-sized inclusions of the intermetallic compound Mn 5 Ge 3 in the Ge matrix. 8 This is shown in trast corresponding to self-assembled Ge 1−x Mn x nanoclusters. In addition several approximately round regions, indicated by the white dashed circles, are visible.…”

“…Mn 5 Ge 3 is a magnetically hard compound 5 with a Curie temperature near room temperature 6 and a hexagonal lattice structure. 7 Proper control of the epitaxy conditions in the GeMn material system allows the deposition of layers containing only Ge 1−x Mn x nanoclusters, Mn 5 Ge 3 precipitates or both, 8 which is of interest for composite magnetic semiconductor applications.…”