Ferromagnetism in Mn-implanted epitaxially grown Ge on Si(100)

Abstract

We have studied ferromagnetism of Mn-implanted epitaxial Ge films on silicon. The Ge films were grown by ultra high vacuum chemical vapor deposition using a mixture of germane (GeH 4 ) and methylgermane (CH 3 GeH 3 ) gases with a carbon concentration less than 1at%, and observed surface rms roughness of about 0.5 nm, as measured by atomic force microscopy.Manganese ions were implanted in epitaxial Ge films grown on Si (100) wafers to an effective concentration of about 16at%, 12at%, 6at% and 2at%. SQUID measurements showed that only the three highest Mn concentration samples are ferromagnetic, while the fourth sample, with [Mn]=2at%, is paramagnetic. X-ray absorption spectroscopy (XAS) and X-ray Magnetic Circular Dichroism (XMCD) measurements indicate that localized Mn moments are ferromagnetically coupled below the Curie temperature. Isothermal annealing of Mnimplanted Ge films with [Mn]=16at% at 300 o C for up to 1200 seconds decreases the magnetization but does not change the Curie temperature, suggesting that the amount of the magnetic phase slowly decreases with time at this anneal temperature. Furthermore, transmission electron microscopy (TEM) and synchrotron grazing incidence x-ray diffraction (GI-XRD) experiments show that the Mn-implanted region is amorphous, and we believe that it is this phase that is responsible for the ferromagnetism. This is supported by our observation that high temperature annealing leads to recrystallization and transformation of the material into a paramagnetic phase. * samaresh@physics.utexas.edu † banerjee@ece.utexas.edu 2

Spin glass dynamics at the mesoscale

“…(23) and (24), the larger t eff w , the larger the thermoremanent magnetization, M TRM (t = 0, T q ), remaining when the magnetic field is removed. That is, the fractional change E Z /∆(t eff w , T q ) diminishes as t eff w increases.…”

“…This picture was invoked in a previous publication [4] to explain the time dependence of zero-field cooled magnetization (ZFC) of (thicker) film of a-Ge:Mn [23], but at the quench temperature T q . This paper extends their treatment to (thinner) films of Cu:Mn [8 -11], and to temperatures below and above T q .…”

Temperature chaos in a Ge:Mn thin-film spin glass

“…Previous experiments have shown this insulating system to exhibit spinglass properties [19,20], not unlike Eu x Sr 1−x S [21], an insulating canonical spin glass system. Further, the behavior of the field cooled magnetization is very similar to that found for the thinnest Cu:Mn films by G.G.…”

“…The experiments were performed on thin amorphous Ge:Mn (11 at.% Mn) films of thickness 155Å [18,19]. Previous experiments have shown this insulating system to exhibit spinglass properties [19,20], not unlike Eu x Sr 1−x S [21], an insulating canonical spin glass system.…”

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

“…A comparative experimental study on the local structures and magnetic interactions of Mn atoms in crystalline and amorphous Ge is important to understand the effect of defects on the distribution * Correspondence: lcolakerol@gtu.edu.tr mechanism of dopants. Despite past intensive studies, controversial issues still remain in the distribution of magnetic moments in Mn-doped crystalline and amorphous Ge thin films [12][13][14][15][16]. We have applied a surface driven approach for the incorporation of Mn into Ge.…”