There is currently widespread interest in the development of novel semiconductors which are ferromagnetic above room temperature. Much of this work has been stimulated by predictions of high temperature ferromagnetism in p-type semiconductors doped with Mn [1]. For GaN, ZnO, and diamond the above room temperature T_c has been predicted, providing simultaneous incorporation of 5% of Mn and 3x10²⁰ holes per cm³ can be achieved. Despite the p-type doping alone, the other big issue in preparation of transition metals rich compounds is an avoiding their inhomogeneous distribution, clustering and precipitations of foreign chemical/magnetic phases. Concerning oxides, several reports on Co, Fe and Mn enriched ZnO, or even in pure, normally nonmagnetic dielectric layers of HfO₂ and VO₂, showed evidence for ferromagnetic behaviour. But there are other that have found no ferromagnetic order originating from the semiconductor itself. Our results decidedly conform to the latter findings in that sense, that occasionally observed ferromagnetic coupling can be attributed to precipitations, in-situ or ex-situ contaminations, not mentioning technical flaws during experimental procedure.
Diametrically different situation is met in arsenides. Here recent advances of MBE resulted in routine fabrication of high and homogenous Mn concentration. Since the same Mn contributes also a hole to the system, carrier mediated ferromagnetism can be easily born. In canonical ferromagnetic semiconductor (Ga,Mn)As T_c above 170 K and a uniform magnetisation corresponding full atomic Mn magnetic moment has been observed. The hole density and Mn concentration dependence of T_c, magnetic anisotropy and other micromagnetic properties are astoundingly well reproduced by model theoretical calculation [1], indicating that (Ga,Mn)As may be the best understood ferromagnet.

[1] T. Dietl et al., Science 287, 1019 (2000), T. Dietl et al., Phys. Rev. B 63, 195205 (2001).

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