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Evidence of Ferromagnetism in the Diluted Magnetic Semiconductor Cuga Mn Te

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Evidence of Ferromagnetism in the Diluted Magnetic Semiconductor Cuga Mn Te Res Dev Material Sci Research & Development Copyright © José inRF CRIMSON PUBLISHERS C Wings to the Research Material Science ISSN: 2576-8840 Research Article Evidence of Ferromagnetism in the Diluted Magnetic Semiconductor CuGa1-xMnxTe 2 José RF1,2*, Carlos Durante R1,3 and Jaime AC1 1Departamento de Física, Venezuela 2Escuela de Ing Industrial, Venezuela 3Escuela de Ciencias Físicas y Matemáticas, Ecuador *Corresponding author: José RF, Departamento de Física, Escuela de Ing Industrial, Venezuela Submission: October 28, 2018; Published: November 30, 2018 Abstract We report on experimental and theoretical evidence of a ferromagnetic phase in the diluted semiconductor CuGa1-xMnxTe 2 using the Ferromagnetic The samples were synthesized by direct fusion of the stoichiometric mixture of the elements, with Mn composition from x=0.05 to 0.25. The data were Resonance (FMR) technique. The FMR spectra were studied as functions of temperature (T) manganese concentration (x) and magnetic field orientation. critical point at about 230K, which is associated with a transition from the ferromagnetic to paramagnetic state. This behaviour is explained assuming interpreted in the framework of a phenomenological model for single domain βuniaxial grains. The temperature variation of the resonance field shows a an effective magnetization following the exponential law MT( ) / M (0)=( 1 − T / TC ) grains with G-factor greater than 3.0.. , with β≈0.40. The resonance field as a function of the field angle displays a well-defined uniaxial symmetry at high Mn concentrations. This uniaxial field is Mn concentration dependent and is due to the formation of ovoid Mn Keywords: Magnetic semiconductors; Magnetic anisotropies; Ferromagnetic resonance; Diluted ferromagnets Introduction connected to point defects responsible for the magnetic ion shelter Diluted magnetic semiconductors (DMS) are alloys in which and p-type carrier concentration induced by holes generation [12]. a magnetic ion is randomly distributed into the solid host and Experimentally, several techniques are available for studying the have been the subject of extensive experimental and theoretical magnetic properties of DMS. Ferromagnetic Resonance (FMR) has work during the last decades [1-5]. The fundamental magnetic, proven to be one of the ideal techniques to study anisotropies and electronic and optical properties of these systems are quite magnetic ordering in magnetic materials [13]. This is because the different from their pure semiconductor counterpart, and over resonance spectrum is very sensitive to properties such as local the last years, it has been shown that these properties are greatly anisotropies, magnetic interactions between intrinsic defects, and magnetic and structural inhomogeneities in the sample. magnetic moments of the ions, leading to strong magnetotransport influenced by the presence of charged carriers and the localized and magnetooptical effects. These phenomena have been widely Ternary I-III-VI2 alloys are well known by their potential studied and understood in Mn-based DMS in which the magnetic applications in the photovoltaic cells, light-emitting-diodes (LEDs), moments of the Mn ions interact antiferromagnetically [6]. More and in nonlinear optical devices [14]. The most studied are those recently, a new generation of transition metal-based compounds such as ZnGeP [7], ZnGeSiN [8], and CuAlS [9], has been attracting [15] and energy gap near to the optimum range for conversion 2 2 2 of the family Cu-III-VI, which possess high absorption coefficient attention because of several exciting new properties such as spin of solar energy [16]. Although this, the capability of diluted injection, carrier induced ferromagnetism, optically controlled magnetic semiconductors of the type I-III-VI2 as candidates for magnetic order, etc. These materials have opened a door into the issue. The aim of this work is addressed to test the ferromagnetic ferromagnetic/semiconductor hybrid structures is an unexplored hybrid structures for applications in spintronics and spin-related properties of the I-III-VI2 diluted magnetic semiconductor CuGa1- field of new magnetic materials and ferromagnetic/semiconductor devices [10,11]. The main features of these alloys are the presence of xMnxTe 2, by means of Ferromagnetic Resonance (FMR). The paper vacancies, interstitial atoms, and anti-site atoms, and it is expected is organized as follows. In the section II the experimental methods that when diluted into the solid matrix, the magnetic ion interacts used to interpret the experimental data. In section IV, our results are briefly described. Section III is devoted to the theoretical model Theoretically, the origin of ferromagnetic ordering in DMS could be are discussed and analyzed. In section V the main results of this with these defects forming pairs with low configuration energy. work are summarized. Volume - 9 Issue - 2 Copyright © All rights are reserved by José RF. 980 Res Dev Material Sci Copyright © José RF Experimental 2 ω 1 = θ ϕϕ−+2 ϕ +2 ϕ −+ 2 H0sin 0 cos( 0HK ) 2MN1 cos 02 N sin 03 N Eθθ Samples of the I-III-VI2 diluted magnetic semiconductor CuGa1- γ sin θ ( ) Mn Te with Mn composition x=0.05 to 0.25 were prepared by ×θ ϕϕ−+ − 2 θ ϕ+ x x 2 H0sin 0 cos( 0HK ) 2MN( 21 N) sin 0 cos2 0Eφφ (4) 2 direct fusion of the stoichiometric mixture of the elements of −θ ϕϕ−+ − θ ϕ+ H0 cos0 sin ( 0HK ) MN( 21 N)sin 2 0 sin 2 0Eθϕ } at least 5N purity in graphite crucibles inside evacuated quartz -6Torr). To minimize the risk of explosion due to Here, E EK are the angular derivatives of the exothermic reaction between the group III element and Te, the anisotropy energy evaluated at the equilibrium positions. Suppose ampoules (≈10 KƟƟ, ϕϕ, EKƟϕ now that our system consisted in arranged single domain uniaxial up to 1100 °C. Kept at this temperature for 24h, the samples were particles (grains) in the form of ellipsoids of rotation (N N =N ; ampoules were heated in a vertical furnace very slowly at 5K/h 1= 2 rocked at regular intervals to achieve a homogeneous mixing of the N3=N|| with saturation magnetization M=N0µ0 0, being µ0 and⊥ liquid phase of the reacting mixture, and then cooled to 500 °C at a V0, the particle moment and particle volume, respectively, and 2 2 /V anisotropy energy given by EK= K sin sin 4 days. To test ferromagnetism in CuGa1-xMnxTe 2 the ferromagnetic in the xy-plane parallel to the plane of the sample ( = rate of 5K/h. At this temperature the ampoules were annealed for ƟƟ ϕ. The field is appliedH resonance spectrometry has been used. The ferromagnetic with the magnetization along the uniaxial axis. At resonance, the Ɵ π/2), Mn concentration, in an x-band VARIAN spectrometer, employing equilibrium angles are resonance field was measured as a function of temperature and magnetization follows approximately0 0 H the external field so the a homemade cylindrical cavity with Q factor of the order of 2000, to the form 2 adjusted in the TE ω Ɵ ≅ π/2, ϕ ≅ϕ so equation (4) is simplified 100 2 = [H0 cosϕH − 2ε M eff − H K sin ϕH ][H0 cosϕH + H K cos2ϕH ] (5) electromagnet mounted onto a 0-360 degrees base that allowed γ mode. The magnetic field is supplied by an us to rotate the sample with respect to the direction of the applied H H H 2 which gives the resonanceHH=−+− field1 for1 any2 orientation, (6) ϕ R 4 2 field. With this, we were able to measure the angular symmetry of 2 of the sample. All spectra were taken at 9.35GHz cavity, and in the where the FMR signal. The magnetic field was applied parallel to the plane temperature range 90 K<T<300 K. The temperature was calibrated 2 ϕ HH1 =KHH[cos 2ϕε −− sin] 2 Meff using a carbon-glass thermometer. 2 HH22=cos2ϕ sin 2 ϕ −− 2 εMH cos2 ϕ( ωγ / ) Theoretical Background 2 K HH eff u H The dynamics of the magnetization in a macroscopic = According to this,0 theH resonance field is uniquely determined0 H ferromagnet is usually described using the Landau-Lifshitz-Gilbert (hard uniaxial axis), such that H ( in the range from ϕ =ϕ =0 (easyR uniaxialR H axis)R to ϕ =ϕ π/2 equation (LLGE) of motion, when the condition 4 M eff (0)≤ H (ϕ )≤ H π/2). In the case dM λ =−×γ (MH )( − MMH ×× ) (1) eff 2 eff π >>HK is2 fulfilled, the FMR field is purely dt M (ωγ/ ) uniaxial and given byHH the≅− simplified − formcos 2ϕ (8) where M is the magnetization; Heff M R KH 2ε M eff E is the magnetic free energy; is a relaxation frequency related where M -N =-∇ E is the effective field, eff || Mn λ = N ⊥is the effective magnetization, Hk is the KOe) is the gyromagnetic ratio for Mn. If our system is considered with the shape of a spheroid (+) or an ovoid (-). Equation (8) is to the viscous damping of the magnetization; and γ=1.4g (GHz/ as a collection of magnetically oriented grains or particles, then the uniaxial field defined as 2K/M, and ε=±1 representing an ellipsoid magnetic free-energy can be expressed as determine the three parameters M , H and g-factor. then compared to the experimentaleff valuesk of the resonance field to 3 θϕ =−•+2∑ 2 + 22θ φ (2) E(,) H M M Nmi i Ksin sin ο i=1 Results and Analysis The FMR spectra of the sample CuGa0.75Mn0.25Te 2 are shown in H , N are the demagnetizing factors of the material, mi the director 0 wherei the first term is the Zeeman energy at a magnetic field cosines of the magnetization M in spherical coordinates, the third Figure 1, for several temperatures and for a fixed field orientation. The FMR absorption is characterized by: (a) sharp low-field peak 0 0), the LLGE signal was detected for temperatures <90K.
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