On origin of room temperature ferromagnetism in wide gap semiconductors

The emerging field of semiconductor spintronics would be dramatically boosted if a semiconductor exhibiting room-temperature ferromagnetism could be found. Here, we discuss the recent stage of the research, paying particular attention to the understanding of observed room temperature ferromagnetism in wide band semiconductors, GaMnN and ZnMnO. Since the spinodal decomposition has been observed in these structures, we consider the possibilities to influence density fluctuations of the alloys to obtain ferromagnetic semiconductors with required functionalities. We contrast these compounds with (In,Mn)As and (Ga,Mn)As, where the ferromagnetism is well understood, albeit well below room temperature

Experimental probing of the interplay between ferromagnetism and localisation in (Ga,Mn)As

The question whether the Anderson-Mott localisation enhances or reduces magnetic correlations is central to the physics of magnetic alloys. Particularly intriguing is the case of (Ga,Mn)As and related magnetic semiconductors, for which diverging theoretical scenarios have been proposed. Here, by direct magnetisation measurements we demonstrate how magnetism evolves when the density of carriers mediating the spin-spin coupling is diminished by the gate electric field in metal/insulator/semiconductor structures of (Ga,Mn)As. Our findings show that the channel depletion results in a monotonic decrease of the Curie temperature, with no evidence for the maximum expected within the impurity-band models. We find that the transition from the ferromagnetic to the paramagnetic state proceeds via the emergence of a superparamagnetic-like spin arrangement. This implies that carrier localisation leads to a phase separation into ferromagnetic and nonmagnetic regions, which we attribute to critical fluctuations in the local density of states, specific to the Anderson-Mott quantum transition.Comment: 8 pages, 3 figure

Genetic Architecture of a Reinforced, Postmating, Reproductive Isolation Barrier between Neurospora Species Indicates Evolution via Natural Selection

A role for natural selection in reinforcing premating barriers is recognized, but selection for reinforcement of postmating barriers remains controversial. Organisms lacking evolvable premating barriers can theoretically reinforce postmating isolation, but only under restrictive conditions: parental investment in hybrid progeny must inhibit subsequent reproduction, and selected postmating barriers must restore parents' capacity to reproduce successfully. We show that reinforced postmating isolation markedly increases maternal fitness in the fungus Neurospora crassa, and we detect the evolutionary genetic signature of natural selection by quantitative trait locus (QTL) analysis of the reinforced barrier. Hybrid progeny of N. crassa and N. intermedia are highly inviable. Fertilization by local N. intermedia results in early abortion of hybrid fruitbodies, and we show that abortion is adaptive because only aborted maternal colonies remain fully receptive to future reproduction. In the first QTL analysis of postmating reinforcement in microbial eukaryotes, we identify 11 loci for abortive hybrid fruitbody development, including three major QTLs that together explain 30% of trait variance. One of the major QTLs and six QTLs of lesser effect are found on the mating-type determining chromosome of Neurospora. Several reinforcement QTLs are flanked by genetic markers showing either segregation distortion or non-random associations with alleles at other loci in a cross between N. crassa of different clades, suggesting that the loci also are associated with local effects on same-species reproduction. Statistical analysis of the allelic effects distribution for abortive hybrid fruitbody development indicates its evolution occurred under positive selection. Our results strongly support a role for natural selection in the evolution of reinforced postmating isolation in N. crassa

Solving the problem of ambiguous paralogy for marker loci : microsatellite markers with diploid inheritance in allohexaploid Mercurialis annua (Euphorbiaceae)

Mercurialis annua is a wind-pollinated annual showing a remarkable sexual-system variation, with hexaploid populations being either monoecious or androdioecious. Hexaploid M. annua is most likely a product of hybridization between diploid M. huetii and tetraploid M. annua; therefore, we developed microsatellite loci by isolating simple sequence repeat (SSR) sequences from the diploid progenitor, cross-amplification tests in M. huetii/M. annua species complex followed by selection of loci amplifying only in M. huetii and hexaploid M. annua, and testing polymorphism in 1 hexaploid population. This protocol resulted in 10 unlinked, polymorphic loci amplifying 4–10 alleles per locus. Due to specific amplification of the diploid part of the genome originating from M. huetii, these loci produce codominantly scored, diploid data for allohexaploid species, thereby simplifying data collection and subsequent analyses. Sequencing of the hexaploid polymerase chain reaction product for all 10 loci and aligning it with M. huetii SSR library sequence confirmed orthology of the characterized loci. Inheritance tests in 4 hexaploid crosses confirmed diploid Mendelian segregation of the new loci

Balance between inbreeding and outcrossing in a nannandrous species, the moss Homalothecium lutescens.

Epiphytic dwarf males on the females present a possible solution to the problem of short fertilization distances in mosses. However, leptokurtic spore dispersal makes dwarf males likely to be closely related to their host shoot, with an accompanying risk of inbreeding. The capacity of a female to harbour a high number of different dwarf males suggests that there may be mechanisms in place that counteract inbreeding, such as polyandry and post-fertilization selection. We have genotyped sporophytes, female host shoots and dwarf males in four populations of the moss Homalothecium lutescens. We found no evidence of selective sporophyte abortion based on level of heterozygosity. The occurrence of entirely homozygous sporophytes together with significantly positive inbreeding coefficients in three of the populations (mean FIS between 0.48 and 0.64) suggest frequent mother-son mating events. However, 23% of all sampled sporophytes had a higher level of heterozygosity compared with the mean expected heterozygosity at the population level. Polyandry was frequent, on average 59% of the sporophytes on a female shoot were sired by distinct fathers. In conclusion, sporadic fertilizations by dwarf males originating from nonhost female shoots appear to counteract strong inbreeding.Heredity advance online publication, 2 September 2015; doi:10.1038/hdy.2015.79