Evidence for temperature dependent moments ordering in ferromagnetic NiMnSb(100)

Abstract

Ristoiu, Delia; Hordequin, Ch.; Nozie`res, J. P.; Pierre, J.; Stadler, Shane; and Idzerda, Y. U., "Evidence for temperature dependent moments ordering in ferromagnetic NiMnSb(100)" (2001). Peter Dowben Publications. 23.

Magnetic, structural, and transport properties of the Heusler alloysCo2MnSiand NiMnSb

“…The second derivative of the (T) curve for NiMnSb is positive at both high and low T, but becomes negative for 60 KϽTϽ120 K. This transition of the second derivative is reflected in the humplike feature of the (T) curve centered at ϳ90 K. A similar shift in the temperature dependence of the resistivity of single-crystal NiMnSb was documented in an earlier paper. 15 In that paper, Borca et al provided evidence of a magnetic phase transition between 80 and 100 K. The observed power-law shift may be attributed to this phase transition. For Co 2 MnSi, 5 K ϳ7 ⍀ cm compares favorably with earlier measurements of single-crystal specimens.…”

“…This value for the longitudinal magnetoresistance at 293 K compares favorably to the earlier results of Borca et al, who ascribed the negative magnetoresistance to the opening of a spin-flip scattering channel above the moment-ordering transition. 15 Figure 6͑b͒ gives a detailed view of the R(H) curve for NiMnSb at low fields. In this unsaturated region, Ϫ100 OeϽH Ͻ100 Oe, we observe a very small anisotropic magnetoresistance of ϳ0.023%.…”

Surface properties of the half-and full-Heusler alloys

“…But when they removed the excess of Sb by a flash annealing, they managed to get a nearly stoichiometric ordered alloy surface being terminated by a MnSb layer, which presented a spin-polarisation of about 67±9% at room temperature [21]. The temperature dependence of the spin moments for such a film was studied by Borca et al [22]. Wijs and de Groot have shown by first-principle calculations that NiMnSb surfaces do not present 100% spin-polarisation and they proposed that at some interfaces it is possible to restore the half-ferromagnetic character of NiMnSb [23].…”

Are half-metallic ferromagnets half metals? (invited)

“…Magnon coupling to these phonon modes should result a dramatic loss in Ni and Mn magnetization and polarization in NiMnSb, well below room temperature, as is observed. 54 In the semi-Heusler alloys, this corresponds to a tilting between neighboring Ni and Mn atoms. In real space, the coupled magnon-phonon mode may cant the spins between Mn next nearest neighbors to form an angle of the order of 60°, while all the Mn moments are misaligned with respect to the nickel moments.…”

“…4͑b͔͒ of NiMnSb are consistent with a crossover in magnetic ordering at 80 to 100 K. At temperatures above this metamagnetic transition, all indications suggest an onset of a large spin minority channel. 54 Associated with the compound structure of all the postulated half metals, there are typically a number of lowenergy transverse and longitudinal optical modes. These optical phonon modes can couple to spin-wave modes and reduce the net magnetization.…”