Neutron scattering study of structural and magnetic properties of hexagonal MnTe

Abstract

Single crystals of hexagonal MnTe (in NiAs structure) have been grown by the physical vapour transport method and investigated by neutron scattering techniques. Lattice parameters and magnetic intensity of Bragg peaks characteristic of the antiferromagnetic order of the first kind have been measured by elastic neutron scattering in the temperature range from T = 10 K to the Néel temperature T N = 310 K. A smooth temperature dependence of the lattice parameter values a and c as well as of the c/a ratio has been found. A brief survey of phonon and magnon modes has been performed at room temperature by inelastic neutron scattering, yielding acoustic phonon branches along a* and c* directions at frequencies below 3 THz and the presence of the magnon mode, already strongly damped due to the vicinity of the magnetic phase transition.

X-ray photoelectron study of NiAs-type MnTe

“…Furthermore, the crystals were subjected to the high temperature annealing (within 900-950 • C) in Te vapour (see Refs. [2,10] and references therein). X-ray diffraction (XRD) measurements of the obtained samples [2] indicated their single-phase structure (H-MnTe) in a form of large grain polycrystals (of order of 1 mm in diameter).…”

“…In fact, MnS, MnSe and MnTe are antiferromagnetics with the respective Neel temperatures (T N ) equal 152 K [7], 247 K [8] and 307 K [9] (see also Refs. [5,10]). Due to the above mentioned peculiarities, H-MnTe has been classified as a "crossroads" material (see Refs.…”

“…the reference list in Ref. [10]). Nevertheless, appearance of the so-called diluted magnetic semiconductors (DMSs) [12] in the late 1970s and their further widespread studies [12][13][14] induced a revival of interest in hexagonal MnTe.…”

Are values of parameters describing magnetic properties of crystal really fixed?

“…MnTe crystallizing in NiAs structure is a good example of such semiconductor. Only due to an increase of Mn Te bond length between 4.2 K (the liquid helium temperature) and 295 K in this compound (see, e.g., [36]) the expected change of the exchange integral should be as high as J 1 /J 1 ≈ 0.07. For Ga 1−x Mn x As which exhibit the ferromagnetic properties up to 170 K the expected difference between the low and high temperature values of the exchange integral J is much smaller ( J /J ≈ 0.002).…”

“…The bulk MnTe (crystallizing in NiAs structure) exhibits T N = 310 K [36], whereas T N = 284 K was observed for MnTe layer with the same structure grown on Al 2 O 3 substrate [37]. The T N value determined by the temperature dependence of the magnon frequency (which is given by the combination of the exchange integrals) observed by Raman scattering for zinc blende (ZB) modification of MnTe is also different for thin layers of this compound grown on GaAs and Cd 1−x Zn x Te substrates, as it was shown in [38].…”