Spin-glass-like behavior of Ge:Mn

TL;DR

This study investigates the magnetic properties of Ge:Mn dilute magnetic semiconductors, revealing spin-glass-like frozen states at low temperatures through magnetization and susceptibility measurements.

Contribution

It provides detailed experimental evidence of spin-glass behavior in Ge:Mn, a dilute magnetic semiconductor, highlighting its non-conventional magnetic state at low temperatures.

Findings

Freezing temperatures of 12K and 15K for different Mn concentrations.

Frequency-dependent susceptibility peaks indicating spin-glass dynamics.

Magnetization relaxation effects consistent with a frozen magnetic state.

Abstract

We present a detailed study of the magnetic properties of low-temperature-molecular-beam-epitaxy grown Ge:Mn dilute magnetic semiconductor films. We find strong indications for a frozen state of Ge_{1-x}Mn_{x}, with freezing temperatures of T_f=12K and T_f=15K for samples with x=0.04 and x=0.2, respectively, determined from the difference between field-cooled and zero-field-cooled magnetization. For Ge_{0.96}Mn_{0.04}, ac susceptibility measurements show a peak around T_f, with the peak position T'_f shifting as a function of the driving frequency f by Delta T_f' / [T_f' Delta log f] ~ 0.06, whereas for sample Ge_{0.8}Mn_{0.2} a more complicated behavior is observed. Furthermore, both samples exhibit relaxation effects of the magnetization after switching the magnitude of the external magnetic field below T_f which are in qualitative agreement with the field- and zero-field-cooled magnetization measurements. These findings consistently show that Ge:Mn exhibits a frozen magnetic state at low temperatures and that it is not a conventional ferromagnet.