Due to their striking magnetic properties, magnetic iron nitride-based (FexN and GayFexN) compounds are attracting attention as building blocks for high-density magnetic recording write heads and media. We have recently demonstrated that we can control the aggregation of GaxFe4-xN nanocrystals (NCs) embedded in a III-nitride matrix. By tuning the growth parameters, and consequently the stoichiometry of the NCs, we can dictate the magnetic response of the system to be either ferromagnetic or antiferromagnetic [1,2]. Here we report on the influence of Mn co-doping on the magnetic properties of self-assembled planar arrays of GaxFe4-xN:Mn NCs embedded in GaN. The samples, fabricated by means of metal organic vapor phase epitaxy (MOVPE) according to a protocol already reported [1], have all the same nominal Fe content and differ for the Mn nominal content. The samples are characterized by transmission electron microscopy and x-ray diffraction. We have measured, by SQUID, hysteresis loops at different temperatures in the 5-300 K range, the thermal dependence of the magnetization at different values of the applied magnetic field (in zero-field-cooling and field-cooling modes) and the field-dependent isothermal and demagnetized remanence, allowing the construction of the Delta_M plots. In all the investigated samples, the magnetic analysis reveals the presence of a ferromagnetic component and of a paramagnetic one. The former, assigned to the Ga x Fe 4-x N:Mn NCs, decreases with increasing the Mn content in the samples, whereas the latter increases and is ascribable to diluted Fe and/or Mn ions in the GaN matrix. The whole of the results indicates that Mn acts so as to hinder the formation and/or the growth of the NCs. The magnetothermal behavior of the samples is well explained considering that magnetically relaxing NCs coexist with non-relaxing ones. The magnetic moments of the larger NCs are thermally stable in the spanned temperature range, also due to the fact that dipolar interactions favor the formation of magnetic aggregates. The magnetic moments of the smaller NCs undergo a superparamagnetic-like relaxation. We can consider that, at low-temperature, the small NCs are part of the magnetic aggregates, as their moments are blocked under the action of dipolar interactions that compete with their magnetic anisotropy. With increasing temperature, the moments of the small NCs relax almost independently, thus leaving the magnetic aggregates. [1] A. Navarro-Quezada et al. Appl. Phys. Lett. 101 (2012) 081911 [2] A. Grois et al., Nanotechnol. 25 (2014) 395704
Magnetic properties of phase-separated GaxFe4-xN:Mn in a GaN matrix
L. Del Bianco;F. Spizzo;
2017
Abstract
Due to their striking magnetic properties, magnetic iron nitride-based (FexN and GayFexN) compounds are attracting attention as building blocks for high-density magnetic recording write heads and media. We have recently demonstrated that we can control the aggregation of GaxFe4-xN nanocrystals (NCs) embedded in a III-nitride matrix. By tuning the growth parameters, and consequently the stoichiometry of the NCs, we can dictate the magnetic response of the system to be either ferromagnetic or antiferromagnetic [1,2]. Here we report on the influence of Mn co-doping on the magnetic properties of self-assembled planar arrays of GaxFe4-xN:Mn NCs embedded in GaN. The samples, fabricated by means of metal organic vapor phase epitaxy (MOVPE) according to a protocol already reported [1], have all the same nominal Fe content and differ for the Mn nominal content. The samples are characterized by transmission electron microscopy and x-ray diffraction. We have measured, by SQUID, hysteresis loops at different temperatures in the 5-300 K range, the thermal dependence of the magnetization at different values of the applied magnetic field (in zero-field-cooling and field-cooling modes) and the field-dependent isothermal and demagnetized remanence, allowing the construction of the Delta_M plots. In all the investigated samples, the magnetic analysis reveals the presence of a ferromagnetic component and of a paramagnetic one. The former, assigned to the Ga x Fe 4-x N:Mn NCs, decreases with increasing the Mn content in the samples, whereas the latter increases and is ascribable to diluted Fe and/or Mn ions in the GaN matrix. The whole of the results indicates that Mn acts so as to hinder the formation and/or the growth of the NCs. The magnetothermal behavior of the samples is well explained considering that magnetically relaxing NCs coexist with non-relaxing ones. The magnetic moments of the larger NCs are thermally stable in the spanned temperature range, also due to the fact that dipolar interactions favor the formation of magnetic aggregates. The magnetic moments of the smaller NCs undergo a superparamagnetic-like relaxation. We can consider that, at low-temperature, the small NCs are part of the magnetic aggregates, as their moments are blocked under the action of dipolar interactions that compete with their magnetic anisotropy. With increasing temperature, the moments of the small NCs relax almost independently, thus leaving the magnetic aggregates. [1] A. Navarro-Quezada et al. Appl. Phys. Lett. 101 (2012) 081911 [2] A. Grois et al., Nanotechnol. 25 (2014) 395704I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
