An investigation of the antiferromagnetic transition of CrN

Abstract

The preparation of nitrides of chromium has been studied in detail. Oxygen free samples of Cr1.000Nx, x ranging from 0.997 to 0.980, have been prepared by equilibrating at temperatures from 850 to 1048 °C in one atmosphere pressure of nitrogen. Results of the temperature dependences of expansivity, lattice parameters, magnetic susceptibility and electrical resistivity of CrN of various compositions are reported. The antiferromagnetic → paramagnetic transformation in CrN exhibits temperature hysteresis and is shown to be a transformation of the first kind. The transformation temperature of Cr1.000N0.997 is 286 °K.

Epitaxial suppression of the metal-insulator transition in CrN

“…The data clearly shows a 0.14% increase of lattice constant at 270-284 K, indicating a phase transition for the polycrystalline CrN layer. The 0.14% increase is within previously reported values of 0.08% 7 and 0.24%, 11 where the relatively large difference between these studies is likely due to impurities, particularly for bulk samples, and substrate induced stress for the thin film studies.…”

“…3,4 Electronic transport studies report controversial results for CrN, including (i) values for the resistivity ρ at room temperature range over more than two orders of magnitudes, from 1.7×10 -3 to 3.5×10 -1 Ωcm, 3,[5][6][7][8][9][10] even when only considering the most reliable data for single crystal CrN layers; (ii) the temperature dependence of ρ shows metallic behavior with dρ/dT > 0 in some studies, 6,7,11 but an increase in ρ with decreasing temperature in other reports, 3,5,9,12 which has been attributed to the presence of a band gap 5 or carrier localization due to crystalline defects 13 or N-vacancies; 14 (iii) some studies report a discontinuity in ρ(T) at 260-280 K, 3,6,7,14 which is associated with a magnetic and structural phase transition from a paramagnetic NaCl structure at room temperature to a low-temperature antiferromagnetic orthorhombic P nma phase 11,15 with a 0.56-0.59% higher density, 11 and a 25% lower bulk modulus, 16 while other reports show no evidence for a phase transition in the ρ(T)-curves. 5,7,9 Electronic structure calculations suggest that magnetic stress relief couples magnetic ordering with the structural phase transition, 17 and that CrN exhibits a band gap if the Hubbard Coulomb interaction term is sufficiently large.…”

“…11 In addition, the CrN peak intensity also decreases with decreasing temperature, which may be due to local strain fields associated with the suppressed phase transition. The change of the CrN lattice constant vs T is plotted in Fig.…”

A comparative study of transport properties in polycrystalline and epitaxial chromium nitride films

“…3,4 Considerable experimental and theoretical work have demonstrated that CrN undergoes a magnetic and structural phase transition from a paramagnetic NaCl structure at room temperature to a low-temperature antiferromagnetic orthorhombic P nma phase at N eel temperature of 273-286 K. [5][6][7] A variety of electrical transport properties in CrN have been observed, such as, a semiconducting behavior with dq/dT < 0, [8][9][10][11] a metallic behavior with dq/dT > 0, [12][13][14] and continuous and discontinuous q(T) curves at 260-280 K. [8][9][10][11][12][13]15 These differences in electrical transport properties have been attributed to the sensitivity of the transport properties to N stoichiometry. 12,15 In addition, the discontinuity in q(T) curves has usually been observed in CrN powders or polycrystalline CrN films, rather than in epitaxial films, suggesting that the epitaxial constraints could affect the transition. 14,16 Therefore, it is necessary to carry out a comparative study of the electrical transport properties of polycrystalline and epitaxial CrN films with different N concentrations in order to clarify the conductance mechanism.…”

Influence of nitrogen growth pressure on the ferromagnetic properties of Cr-doped AlN thin films

“…26 Even if this kind of small cluster existed, one would expect to observe superparamagnetism, instead of the ferromagnetism as we show here. In addition, CrN or Cr 2 N clusters, if present, would not contribute to the observed ferromagnetism, because CrN is antiferromagnetic and Cr 2 N is not ferromagnetic between 85 and 500 K. 27 Thus, the presence of Cr clusters cannot be the source of the enhanced ferromagnetism in AlCrN films grown at low nitrogen pressures.…”