Possible room temperature ferromagnetism in Ca-doped AlP: First-principles study

doi:10.1016/j.jmmm.2013.04.052

Journal of Magnetism and Magnetic Materials

Volume 342, September 2013, Pages 35-37

https://doi.org/10.1016/j.jmmm.2013.04.052 Get rights and content

Highlights

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“d⁰ ferromagnetism” has been found in Ca-doped AlP.
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Unpaired t₂ state of P atoms has an important impact on magnetic properties.
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Room temperature T_C may be expected in Ca-doped AlP.

Abstract

Based on first-principle calculations, we have studied the electronic and magnetic properties of AlP with aluminium vacancy and calcium doping. It was found that while Al vacancy and Ca impurity themselves are nonmagnetic, they generate holes residing in P $2 p$ orbitals that lead to magnetic moments in AlP. The coupling between two Al vacancies in AlP are always antiferromagnetic because of half-filled t₂ level. However, the coupling becomes ferromagnetic with large magnetic energy when vacancies are replaced by nonmagnetic Ca atoms. Moreover, the presence of Ca dopants reduces the formation energy of Al vacancy. These results suggest that Ca-doped AlP is a promising room temperature ferromagnetic semiconductor free of magnetic precipitates, and it may find applications in the field of spintronics.

Introduction

The realization of materials that combine semiconducting behavior with robust magnetism has long been a dream of material physics [1]. Dilute magnetic semiconductors (DMS), which are semiconductors doped with magnetic 3d transition-metal (TM) ions [2], [3], [4], are thought to be ideal materials in this field. For practical applications, ferromagnetism (FM) of DMS must be achieved above room temperature. In the past decade, many efforts have been made toward III–V semiconductors based DMS both theoretically and experimentally, and ferromagnetism above room temperature has been observed [5], [6]. Despite of these successes, however, the origin of the observed ferromagnetism is still controversial. Because these dopants are intrinsically magnetic, they can segregate to form precipitates or clusters in the host semiconductors, which may also contribute to the observed ferromagnetism. For example, embedded cluster induced ferromagnetism in Cr-doped AlN has been confirmed by Cui et al. [7]. New classes of DMS which are free of magnetic precipitates are desirable. Recently, defect-induced ferromagnetism has been observed in undoped oxides [8], [9], [10] and III nitrides [11], [12], which do not contain magnetic 3d TM ions. This type of “d⁰ ferromagnetism” provides a new avenue for searching high temperature ferromagnetic semiconductors. In this work, defect- and doping-induced so-called “d⁰ ferromagnetism” in AlP is investigated by the first-principles calculations.

Section snippets

Methods

The calculations were performed using full-potential linearized augmented plane wave method implemented in the WIEN2K package [13]. The accuracy of the basis set is determined by RK_max=7 and the k-space integration by a mesh of 500 k-points in the full Brillouin zone. All the calculations were carried out with the GGA-PBE [14] scheme for exchange-correlation energy. A 64-atom 2×2×2 supercell is used. For each case the atomic positions are fully relaxed. The concentration of a defect at growth

Results and discussion

Vacancy induced antiferromagnetism. First, we study the ferromagnetism of neutral Al vacancy (V_Al) which is created by removing one Al atom from a 2×2×2 supercell of AlP. The calculated spin-polarization energy $E^{PM - FM}$ (energy difference between the non-polarized and spin-polarized states) is about 102.7 meV, suggesting that the spin-polarized states are more stable. In order to investigate the origin of the spin polarization, Fig. 1 shows the spin-resolved total and partial density of states

Conclusions

In summary, Al vacancy and Ca doping induced magnetism in AlP is carefully studied using DFT-based first-principles electronic structure methods. It shows that AlP containing Al vacancy is antiferromagnetic with high formation energy because of exactly half-filled 2p states of anion neighbors of the vacancy site. However, it becomes ferromagnetic with low formation energy upon unpaired 2p electrons are partly saturated by Ca doping. The large magnetic energy and low formation energy demonstrate

Acknowledgments

This work is partly supported by the National Natural Science Foundation of China under Grant nos. 61006051 and 61177050. The author acknowledges the computational support provided by the Peiliang's Group of Solid States Electronics at China Jiliang University.

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Since the first fabrication of (In, Mn)As diluted magnetic III–V compound semiconductors reported, much effort has been made to find ferromagnetic semiconductors. Mn-doped zinc-blende AlP has more stable ferromagnetic state than Mn-doped AlN, but has received little attention due to its indirect band-gap. Note that, a direct band-gap in AlP nanotubes or strained-single layer AlP film were demonstrated by theoretical calculations. We therefore investigate the magneto-optical properties of Mn-doped AlP by density functional theory within the generalized approximation + U (GGA + U). After Mn doping, an unexpected optical absorption in the visible range was observed compared with pure AlP. The absorption onset exhibited blue shift at highest Mn concentrations (MnP). The high optical adsorption and bandgap tenability in the visible optical range make Mn-doped AlP highly desirable for magneto-optical and lighting applications.
Room-temperature ferromagnetism in alkaline-earth-metal doped AlP: First-principle calculations
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Possible room temperature ferromagnetism in Ca-doped AlP: First-principles study

Highlights

Abstract

Introduction

Section snippets

Methods

Results and discussion

Conclusions

Acknowledgments

Solid State Communications

Science

Applied Physics Letters

Nature Materials

Physical Review B

Applied Physics Letters

Journal of Applied Physics

Physical Review Letters

Applied Physics Letters

Applied Physics Letters

Physical Review Letters