New diluted ferromagnetic semiconductor with Curie temperature up to 180 K and isostructural to the ‘122’ iron-based superconductors

Abstract

Diluted magnetic semiconductors have received much attention due to their potential applications for spintronics devices. A prototypical system (Ga,Mn)As has been widely studied since the 1990s. The simultaneous spin and charge doping via hetero-valent (Ga 3 þ ,Mn 2 þ ) substitution, however, resulted in severely limited solubility without availability of bulk specimens. Here we report the synthesis of a new diluted magnetic semiconductor (Ba 1 À x K x )(Zn 1 À y Mn y ) 2 As 2 , which is isostructural to the 122 iron-based superconductors with the tetragonal ThCr 2 Si 2 (122) structure. Holes are doped via (Ba 2 þ , K 1 þ ) replacements, while spins via isovalent (Zn 2 þ ,Mn 2 þ ) substitutions. Bulk samples with x ¼ 0.1 À 0.3 and y ¼ 0.05 À 0.15 exhibit ferromagnetic order with T C up to 180 K, which is comparable to the highest T C for (Ga,Mn)As and significantly enhanced from T C up to 50 K of the '111'-based Li(Zn,Mn)As. Moreover, ferromagnetic (Ba,K)(Zn,Mn) 2 As 2 shares the same 122 crystal structure with semiconducting BaZn 2 As 2 , antiferromagnetic BaMn 2 As 2 and superconducting (Ba,K)Fe 2 As 2 , which makes them promising for the development of multilayer functional devices.

Theory of Mn-doped II-II-V semiconductors

“…Figure 2(b) shows M theor (x, y) for three values of y (dash-dotted lines) and compares it with the experiment of Ref. [19]. While there is some qualitative agreement, the magnetization suppression is noticeably underestimated, especially for small x.…”

“…Ref. [19] conjectured that this may be due to the formation of nearest neighbor Mn 2 singlets. We will show below that a simple, random statistical distribution of singlets, as initially suggested, cannot explain the Mn and K concentration dependency of the magnetization, while a distribution in thermodynamic equilibrium at temperatures consistent with experimental synthesis can.…”

“…We then show using thermodynamic arguments that singlet formation is responsible for the reduced magnetization in Ref. [19]. We also address the different terminologies used for the effective magnetic interaction between the Mn d and As p states, such as double exchange [11], the Zener p − d model [22], and the RKKY interaction [23][24][25].…”

“…The recent discovery of the I-II-V and II-II-V DMS compounds [17][18][19] provides a way to overcome these difficulties. In contrast to the II-VI and III-V compounds, in the II-II-V ones hole and spin doping are controlled separately.…”

“…In (Ba 0.7 K 0.3 )(Zn 0.85 Mn 0.15 ) 2 As 2 , a T C ∼ 220 K [20] is already higher than ∼ 190 K [3] attained in GaAs:Mn. Unlike GaAs, both p-and n-doped II-II-Vs can be ferromagnetic [19,21], and a coercive field ∼ 10 4 Oe in (Ba,K)(Zn,Mn) 2 As 2 at 2 K [19] is two orders of magnitude larger than in GaAs:Mn. Apart from potential applications [5], the II-II-V DMS are well suited for theoretical study, because (1) the Mn 2+ is isovalent with Zn, (2) charge is doped into the Ba sublayer, spatially and electronically disconnected from the active (Zn,Mn) 2 As 2 layers, and (3) interstitial locations for Mn ions are energetically precluded.…”