Spin–flip transition of L1₀-type MnPt alloy single crystal studied by neutron scattering

Abstract

Magnetic structure, tetragonality, and the spin-flip transition for an L1(0)-type MnPt ordered alloy were studied by neutron scattering using a single-crystal specimen. Tetragonality of the lattice showed strong correlation with the spin-flip transition. Although the spin-flip transition looks like a gradual change of the easy axis in the temperature range between 580 and 770 K, two modes of magnon-gap peaks with different energies were observed in this transition temperature range. Thus, the crystal consists of two regions with different anisotropy energies and the volume fractions of these regions with different spin directions change gradually with temperature. The tetragonality and spin-flip transition are discussed using the hard-sphere model for atomic radii of Pt and Mn. The Invar effect of Mn atoms is proposed using high- and low-spin transitions of Mn moments in analogy with the two-γ model of Fe moments in FeNi Invar alloy.

First-principles study of magnetic properties ofL10-ordered MnPt and FePt alloys

“…The obtained values of lattice parameters and magnetic moments of MnPt and FePt magnetic ground states are in good agreement with the corresponding experimental data [8][9][10][11][22][23][24] and previous first-principles calculations. [25][26][27][28][29][30][31][32][33][34][35][36] Pt atoms are found to have either small ͑0.39 for MnPt, 0.34 for FePt for Model 3͒ or negligible magnetic moments ͑Models 1 and 2͒.…”

“…Such a small value for MnPt explains the experimentally observed controversy and sensitivity of the MCA to changes in composition and temperature. [8][9][10][11] Besides, being small, the out-of-plane MCA of MnPt is sensitive to the details of first-principles calculations. 26 The out-of-plane MCA of FePt is in good agreement with previous first-principles calculations.…”

“…[8][9][10][11][16][17][18] The small ͑ϳ7 meV͒ energetic preference of FM over AFM in FePt at T = 0 is in 25, it is shown that the correct FM ground state of FePt is predicted only when the generalized gradient approximation is used due to the more accurate estimation of lattice constants. The obtained values of lattice parameters and magnetic moments of MnPt Model 1͑AFM͒ and FePt Model 3͑FM͒ are in good agreement with the corresponding experimental data [8][9][10][11][22][23][24] and previous first-principles calculations. [25][26][27][28][29][30][31][32][33][34][35][36] Pt atoms are found to have either small or negligible magnetic moments.…”

“…1͒ with small tetragonal distortions. At room temperature, MnPt is found experimentally [8][9][10][11] to have antiferromagnetic order with aniferromagnetic coupling between adjacent Mn atoms in the ͑001͒ plane at distance a / ͱ 2 and ferromagnetic coupling between two adjacent Mn atoms in the ͓001͔ direction at distance c ͑see Model 1 in Fig. 1͒.…”

Crystal and magnetic structure of antiferromagnetic Mn2PtPd

“…For these two models we practically obtained the same residuals, which shows that we are not able to determine the moment direction within the tetragonal ab plane. It has been reported that MnPt exhibits two different magnetic structures [30]. At high temperatures above 750 K, the Mn moment lies in the basal plane whereas it undergoes a spin-flip transition in a broad temperature region ranging from 750 to 570 K, leading to a magnetic structure with Mn moments aligned parallel to the tetragonal c axis.…”