Full-Potential Study of Half-Metallic Ferromagnetism in CdTMO2 (TM=Fe, Co and Ni)

S. Amari, S. Méçabih, B. Abbar, B. Bouhafs

Laboratoire de Modélisation et de Simulation en Sciences des Matériaux,Département de Physique Université Djillali Liabès, Sidi Bel-Abbes, Algérie

Correspondence to: S. Méçabih, Laboratoire de Modélisation et de Simulation en Sciences des Matériaux,Département de Physique Université Djillali Liabès, Sidi Bel-Abbes, Algérie.

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Abstract

In this work, we present an ab initio calculation for the structural, electronic and magnetic properties of CdTMO₂ (TM=Fe, Co and Ni) compound. The calculations are performed by a developed full-potential augmented plane wave plus local orbitals (FP-L/APW+lo) method within the spin density functional theory. As exchange-correlation potential we used the generalized gradient approximation GGA form and GGA+U (where U is the Hubbard correlation terms). We have performed total energy calculations of these compounds in the chalcopyrite structure. We present a comparative study between the electronic structures, total and partial densities of states and local moments calculated within GGA and GGA+U. Furthermore, we predict the values of spin-exchange splitting energies Δ_x(d) and Δ_x(p-d) and exchange constants N_0α and N_0β produced by the transition metal 3d states. Our calculations show the half-metallic behavior of these ferromagnetic compounds. 

http://article.sapub.org/10.5923.j.ajcmp.20120202.01.html 

3.2. Electronic Band Structure and Density of States

 The exchange constants N₀α and N_0β show the contribution of the valence and conduction bands in the process of exchange and splitting, and can be related to the spin splitting at the gamma symmetry point of a band structure. The effect of the sp-d exchange on the band structure of a host semiconductor in the mean-field approximation is discussed in[21]. These parameters, N₀α and N₀β, are calculated directly from the conduction band-edge spin-splitting and valence band-edge spin-splitting of CdTMO₂ (TM=Fe, Ni and Co)using the following relations[21,22]:

where is half of the spin magnetic moment of TM ions and x is TM concentration. The calculated values of N₀α and N_0β are presented in Table 3. We can deduce the effective d-band exchange splitting Δ_xd which is defined as the separation between the corresponding spin up and spin down peaks. Another important exchange splitting energy is of the top of the valence bands for spin up and spin down. Our results are listed in Table 3. One can notice that the GGA+U values are very large than GGA results. This is due to the fact that the GGA+U extensively influenced the TM-d states.

 

3.3. Magnetic Properties

The calculated total and local magnetic moments for CdTMO₂ (TM=Fe, Ni and Co) calculated using GGA and GGA+U are presented in Table 2. The main source of magnetization in these materials is the unfilled transition metal-3d states. The nature of attraction in these diluted magnetic semiconductors can be described by the sp-d exchange splitting. The results show that the total magnetic moments generally come from the TM ions with a small contribution of Cd and O sites. Those magnetic moments are parallel to the TM ions; this may be understood as the tunneling of spin-up impurity states into the neighboring atoms. The p–d hybridization reduces the total magnetic moments of the TM atoms from its free space charge value and produces small local magnetic moments on the non-magnetic Cd and O sites. When we used the GGA+U, we see that the magnetic moments of TM ions increase while those of Cd and O decrease.