When the rare earth mononitrides (RENs) first burst onto the scientific scene in the middle of last century, there were feverish dreams that their strong magnetic moment would afford a wide range of applications. For decades research was frustrated by poor stoichiometry and the ready reaction of the materials in ambient conditions, and only recently have these impediments finally been overcome by advances in thin film fabrication with ultra-high vacuum based growth technology. Currently, the field of research into the RENs is growing rapidly, motivated by the materials demands of proposed electronic and spintronic devices. Both semiconducting and ferromagnetic properties have been established in some of the RENs which thus attract interest for the potential to exploit the spin of charge carriers in semiconductor technologies for both fundamental and applied science. In this review, we take stock of where progress has occurred within the last decade in both theoretical and experimental fields, and which has led to the point where a proof-of-concept spintronic device based on RENs has already been demonstrated. The article is organized into three major parts. First, we describe the epitaxial growth of REN thin films and their structural properties, with an emphasis on their prospective spintronic applications. Then, we conduct a critical review of the different advanced theoretical calculations utilised to determine both the electronic structure and the origins of the magnetism in these compounds. The rest of the review is devoted to the recent experimental results on optical, electrical and magnetic properties and their relation to current theoretical descriptions. These results are discussed particularly with regard to the controversy about the exact nature of the magnetic state and conduction processes in the RENs.Comment: 34 pages, 14 figure

We report an interplay between magnetism and charge transport in the ferromagnetic semiconductor GdN, pointing to the formation of magnetic polarons centred on nitrogen vacancies. The scenario goes some way to resolving a long-standing disagreement between the measured and predicted Curie temperature in GdN. It further constitutes an extension of concepts that relate closely to the behaviour of ferromagnetic semiconductors generally, and EuO in particular.PACS numbers: 75.50. Pp, Intrinsic ferromagnetic semiconductors, which offer the freedom to dope into specific conducting channels without destroying their magnetic behaviour, are of obvious technological interest. From a fundamental point of view they are again interesting; it is a substantial challenge to understand the interplay between their magnetic and transport properties. Among the earliest discovered, and even now the most studied, is EuO, which shows a magnetoresistance as large as thirteen orders of magnitude across the metal-insulator transition at the Curie temperature (T C ) [1][2][3], the largest in any compound. The strong transport-magnetism interplay is further emphasised by the enhanced T C seen in electron-doped samples [4,5]. Debate continues about whether the ferromagnetic transition is homogeneous [2,6,7] or whether it involves magnetic polarons nucleating around magnetic impurities [3,[8][9][10][11][12].GdN, the prototypical rare-earth nitride compound, provides a rich set of comparisons with EuO. Divalent Eu and trivalent Gd share the same half-filled 4f shell, with S = 7/2, L = 0, and a net moment of 7 µ B . They share also the same rock salt structure, their reported T C are both near 70 K [13][14][15][16], and GdN also shows a strong magnetoresistance at T C [13,17]. Theoretical treatments of reproduce the measured electronic band features well, showing agreement as regards its semiconductor nature [13,14], the direct band gap [22][23][24], and features in the conduction-band density of states [13,25]. Even more important for device development is that GdN, unlike EuO, has a dispersive valence band of delocalised nitrogen states, which raises the possibility that it can support both n− and p−type conduction. Its potential in realistic spintronics has already been demonstrated by its use in a spin filter [26].In contrast the ferromagnetic exchange mechanism is still poorly understood. The atomic-like nature of the 4f electrons necessitates indirect exchange, but those levels lie too far below the Fermi level to call on the third-order perturbation theory applied to EuO [4,27,28]. The validity of a proposed exchange channel involving the excited Gd 4f8 level is uncertain [29]; in particular note these levels are similarly far from Fermi level [25]. Small energy differences are found among various spin orderings determined within the LDSA+U treatment that has successfully reproduced the band structure, but they lead to an estimated T C below 25 K [30], far below the experimental values. There is even a 1980 report [31], raised again re...

A precise measurement of p̄p elastic scattering in the Coulomb-strong interaction interference region was performed at the CERN Sp̄pS Collider at a centre-of-mass energy of 541 GeV. The ratio of the real to the imaginary part of the forward elastic scattering amplitude was found to be ρ = 0.135 ± 0.015. The slope of the exponential fall off of the strong interaction part was also measured to be b = 15.5 ± 0.1 GeV−2