Magnetic Structures and Phase Transformations in Mn-Based CuAu-I Type Alloys

Abstract

Investigations of the magnetic properties in the ordered CuAu-I-type manganese alloys are reviewed. The formation of the ordered phase and the possible magnetic structures are discussed. New experimental results for the Mn-Ni, Mn-Pd, and Mn-Pt systems are reported. Neutron diffraction shows the basic antiferromagnetic structure to be the same for all the alloys investigated. In MnPt a magnetic-structure transformation has been observed. Below 800°K the magnetic moments turn from the basal plane gradually to the tetragonal axis. The variation of the transition temperature in the Mn-Pt system as well as that of the Néel temperature in the Mn-Ni, Mn-Pd, and Mn-Pt systems with concentration were measured and are theoretically analyzed. The dependence of lattice parameters on concentration and temperature was determined. The lattice parameters suffer a significant but continuous change near the Néel temperature which is attributed to Mn-Mn exchange interaction. Magnetic susceptibility measurements support the neutron-diffraction results. The increase in susceptibility, observed by several authors at lower temperatures, is found to be a result of contaminations.

Electrical and Magnetic Properties, and Electronic Structures of Pseudo-Gap-Type Antiferromagnetic <I>L</I>1<SUB>0</SUB>-Type MnPt Alloys

“…In detail, the excess Mn or Pt atoms substituted in the opponent sites increase the DOS at E F , , together with the calculated electronic specific heat coefficient e cal given from the results of the DOS and eq. (6). As shown in the figure, the concentration dependences of e and e cal accord with each other, however, e deviates from e cal in the concentration range less than 50% Pt.…”

“…Their crystal structure was identified as an L1 0 -type single phase by X-ray powder diffraction and the room temperature lattice constants were in agreement with the data in literatures. [5][6][7] The mass density of the specimens was examined by using toluene as a working liquid. The alloy compositions were confirmed by an inductively coupled plasma (ICP) analysis and also decided from the density derived from the lattice constants.…”

“…[1][2][3][4] The crystal structure of these alloys is a B2 (CsCl)-type cubic phase at high temperatures and transforms into an L1 0 (CuAu-I)-type tetragonal phase with a diffusionless martensitic transformation process at low temperatures. From neutron diffractions and magnetic data, [5][6][7][8][9][10] it has been reported that the L1 0 -type phase exhibits a collinear antiferromagnetic structure and MnNi, MnPd and MnPt equiatomic alloys have a very high Néel temperature T N of about 1100, 780 and 970 K, respectively.…”

Asymmetry effects in atomically resolved STM images of Cu(014)-O and W(100)-O surfaces measured with MnNi tips

“…A magnetic moment of 4.06 B was obtained for the Mn magnetic moment in the AF-I structure, which compares with a theoretical value of 3.29 B obtained by Sakuma 48 and experimental values of 3.8-4.0 B obtained by neutron diffraction. 41,42 As the MnNi tips used in the experiments were polycrystalline, we have investigated both ͓111͔-and ͓001͔-oriented tips. The tip simulations were carried out without spin polarization as the magnetic order of the tip was not deemed important in the context of the experimental results.…”

“…47 The MnNi bulk crystal with CuAu-I-type structure ͑symmetry group P4 / mmm͒ was simulated using the experimentally obtained lattice parameters of a = 3.74 Å and c = 3.52 Å. 41,42 The validity of the calculations was tested by performing spin-polarized calculations on the possible bulk magnetic structures described by Sakuma. 48 The antiferromagnetic ͑AF͒-I-type structure was found to be the ground state magnetic structure at 171 and 56 meV/atom below the ferromagnetic and AF-II-type antiferromagnetic structures.…”