Magnetic and structural properties of GeMn films: precipitation of intermetallic nanomagnets

TL;DR

This study investigates the nanostructure and magnetic properties of GeMn films, revealing ferromagnetic Mn_5Ge_3 precipitates formed during low-temperature growth, which influence the films' superparamagnetic and ferromagnetic behavior.

Contribution

It provides detailed insights into the formation, composition, and magnetic effects of Mn_5Ge_3 nanoinclusions in GeMn films fabricated at low temperatures.

Findings

Precipitates identified as Mn_5Ge_3 ferromagnetic compound

Precipitate volume decreases with lower substrate temperature

Magnetic behavior varies with temperature, showing superparamagnetism and ferromagnetism

Abstract

We present a comprehensive study relating the nanostructure of Ge_0.95Mn_0.05 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 T_S as low as 70 deg. Celsius. 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 Mn_5Ge_3. The volume and amount of these precipitates decreases with decreasing T_S. Magnetometry of the films containing precipitates reveals distinct temperature ranges: Between the characteristic ferromagnetic transition temperature of Mn_5Ge_3 at approximately room temperature and a lower, T_S dependent blocking temperature T_B the magnetic properties are dominated by superparamagnetism of the Mn_5Ge_3 precipitates. Below T_B, 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.