Observation of spin-glass behavior in homogeneous (Ga,Mn)N layers grown by reactive molecular-beam epitaxy

Abstract

We present a detailed study of the magnetic properties of ͑Ga,Mn͒N layers grown directly on 4H-SiC substrates by reactive molecular-beam epitaxy. X-ray diffraction and transmission electron microscopy demonstrates that homogeneous ͑Ga,Mn͒N alloys of high crystal quality can be synthesized by this growth method up to a Mn-content of 10-12 %. Using a variety of magnetization experiments ͑temperature-dependent dc magnetization, isothermal remanent magnetization, frequency and field dependent ac susceptibility͒, we demonstrate that insulating ͑Ga,Mn͒N alloys represent a Heisenberg spin-glass with a spin-freezing temperature around 4.5 K. We discuss the origins of this spin-glass characteristics in terms of the deep-acceptor nature of Mn in GaN and the resulting insulating character of this compound.

Spin-glass-like behavior of Ge:Mn

“…Sample Ge 0.96 Mn 0.04 Such a FC-ZFC difference is often interpreted as a fingerprint for spin glass systems. [7,16] Another explanation is provided by a blocking transition of superparamagnetic particles.…”

“…Furthermore, χ ′ (T ) curves for different measuring frequencies overlap for temperatures higher than the peak temperature. Such a behavior is observed in many spin glass and disordered magnetic systems [7,19,26,27,28,29].…”

“…Reasonable results are obtained in different systems by fitting with logarithmic [7], power law [37], as well as stretched exponential [38] time dependencies.…”

“…As an example, the observation of a spin glass phase in Mn-doped II-VI DMSs like Zn 1−x Mn x Te, [4] Cd 1−x Mn x Te, [5,6] and Cd 1−x Mn x Se (x > 0.2) [6] has been reported more than two decades ago. Recently, spin glass behavior was discovered for the III-V diluted magnetic semiconductors Ga 1−x Mn x N with a spin freezing temperature of T f = 4.5 K (x ≈ 0.1) [7] and Te-doped Ga 1−x Mn x As with T f = 30 K (x = 0.085). [8] As the first ferromagnetic group-IV DMS, Park et al reported in 2002 the growth of Ge 1−x Mn x with T C up to 116 K for x = 0.033.…”

“…For the sample Ge 0.96 Mn 0.04 studied here, [7] and C 1 = 0.005 for Cu:Mn. [31] For superparamagnetic particles, Dormann et al distinguish three different types of dynamical behavior, depending on the interparticle interaction strength: (1) non-interacting particles for 0.10 < C 1 < 0.13 (theory), (2) weak interaction regime (inhomogeneous freezing) with 0.03 < C 1 < 0.06, and (3) medium to strong interaction regime (homogeneous freezing) at 0.005 < C 1 < 0.02.…”