Damped spin-wave excitations in the itinerant antiferromagnet $\ensuremath{\gamma}\text{\ensuremath{-}}{\mathrm{Fe}}_{0.7}{\mathrm{Mn}}_{0.3}$

Damped spin-wave excitations in the itinerant antiferromagnet $γ − {Fe}_{0.7} {Mn}_{0.3}$

S. Ibuka, S. Itoh, T. Yokoo, and Y. Endoh

Phys. Rev. B 95, 224406 – Published 5 June 2017

Abstract

The collective spin-wave excitations in the antiferromagnetic state of $γ − {Fe}_{0.7} {Mn}_{0.3}$ were investigated using the inelastic neutron-scattering technique. The spin excitations remain isotropic up to high excitation energy, $ℏ ω = 78$ meV. The excitations gradually become broad and damped above 40 meV. The damping parameter $γ$ reaches 110(16) meV at $ℏ ω = 78$ meV, which is much larger than that for other metallic compounds, e.g., ${CaFe}_{2} {As}_{2}$ (24 meV), ${La}_{2 - 2 x} {Sr}_{1 + 2 x} {Mn}_{2} O_{7}$ (52–72 meV), and ${Mn}_{90} {Cu}_{10}$ (88 meV). In addition, the spin-wave dispersion shows a deviation from the relation ${(ℏ ω)}^{2} = c^{2} q^{2} + Δ^{2}$ above 40 meV. The group velocity above this energy increases to 470(40) meVÅ, which is higher than that at the low energies, $c = 226 (5)$ meVÅ. These results could suggest that the spin-wave excitations merge with the continuum of the individual particle-hole excitations at 40 meV.

Received 7 December 2016
Revised 7 March 2017

DOI:https://doi.org/10.1103/PhysRevB.95.224406

Physics Subject Headings (PhySH)

Antiferromagnetism Spin waves

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

S. Ibuka^1,2,*, S. Itoh^1,2,3, T. Yokoo^1,2,3, and Y. Endoh^1,4,5

¹Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba 305-0801, Japan
²Materials and Life Science Facility, J-PARC Center, Tokai, Ibaraki 319-1195, Japan
³Department of Materials Structure Science, School of High Energy Science, Graduate University for Advanced Studies, Tsukuba 305-0801, Japan
⁴RIKEN Center for Emergent Matter Science, Wako 351-0198, Japan
⁵Department of Physics, Tohoku University, Aramaki Aoba, Sendai 980-8578, Japan

^*ibuka.em@gmail.com

Article Text (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 95, Iss. 22 — 1 June 2017

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
(a) Brillouin zone perpendicular to [011] for $γ$ -FeMn. The open and solid circles represent the nuclear and magnetic zone centers, respectively. The black solid lines represent the full zone. The green and blue dashed lines represent the reduced magnetic zones for the single-SDW structure. The red dotted lines represent the reduced magnetic zone for the triple-SDW structure. The orange dotted arrow shows the measurement direction for Figs. 2 and 5. (b) Typical measurement condition for the neutron-scattering experiments described in the reciprocal space. The gray arrows represent the crystal directions for [100], [011], and $[0 \bar{1} 1]$ . The red point represents the magnetic zone center $Q_{AF} = (0, 1, 1)$ . The red rectangular plate represents the reduced magnetic zone for the triple-SDW structure, which corresponds to the red dotted rectangle in (a). The green arrows represent the initial and final wave vectors of the neutron, $k_{i}$ and $k_{f}$ , and the scattering vector $Q$ with $E_{i} = 200$ meV, respectively. The blue curved surfaces represent the measuring surfaces for the constant energy $ℏ ω = 0$ and 100 meV.
Reuse & Permissions
Figure 2
$ℏ ω - q_{[0 \bar{1} 1]}$ map around $Q_{AF}$ at $T = 14$ K and $E_{i} = 33$ meV.
Reuse & Permissions
Figure 3
(a)–(d) $q_{[0 \bar{1} 1]} - q_{[100]}$ maps in ${Fe}_{0.7} {Mn}_{0.3}$ at $T = 14$ K, which show the reciprocal planes perpendicular to [011] centered at $Q_{AF}$ . $ℏ ω$ equals (a) $19 \pm 3$ , (b) $48 \pm 5$ , (c) $78 \pm 10$ , and (d) $100 \pm 22$ meV. The errors of $ℏ ω$ denote the $ℏ ω$ range which the peaks cover. For example, for (a), energy resolution is $\pm 0.5$ meV. The average $ℏ ω$ for the left edge $[- 0.1$ 0 0], center, and right edge [0.1 0 0] of the peak is 16.5, 19, and 21.5 meV, respectively. $E_{i}$ equals (a) 33, (b) 82, (c) 207, and (d) 372 meV. For clarity, background intensities were subtracted.
Reuse & Permissions
Figure 4
Dispersion relation of the spin-wave excitations in ${Fe}_{0.7} {Mn}_{0.3}$ at $T = 14$ K. The green triangles, red circles, and blue inverted triangles represent dispersion in [100], [110], and [111], respectively. The vertical error bars represent the energy resolution. The horizontal bars represent the fitting error. The black dashed and solid curves show fits with Eq. (1). The black solid straight line shows a linear fit. The green and blue dashed curves show the dispersion relations previously reported for ${Fe}_{0.7} {Mn}_{0.3}$ [35] at $T = 0$ K and ${Fe}_{0.47} {Mn}_{0.53}$ [36] at RT, respectively. The nearest zone boundary is located at $q = 0.88$ Å $^{- 1}$ .
Reuse & Permissions
Figure 5
$q_{[0 \bar{1} 1]}$ cut at $ℏ ω$ of (a) 100, (b) 78, (c) 41, and (d) 12.5 meV through $Q_{AF}$ . The measured $q$ position corresponds to the orange dotted line in Fig. 1. The black bars represent the $q$ resolutions. The energy widths of the data points are (a) $\pm 18$ , (b) $\pm 7$ , (c) $\pm 1.6$ , and (d) $\pm 0.5$ meV. $E_{i}$ equals (a) 372, (b) 207, (c) 72, and (d) 33 meV. The solid lines represent the fits.
Reuse & Permissions
Figure 6
(a) $ℏ ω$ dependence of the damping parameter $γ$ for ${Fe}_{0.7} {Mn}_{0.3}$ at $T = 14$ K. The black solid lines are guides to the eyes. The purple squares show $γ$ previously reported for ${Fe}_{0.7} {Mn}_{0.3}$ [35] at RT. The green dashed and blue dotted lines show $γ$ for ${CaFe}_{2} {As}_{2}$ [43] and ${La}_{2 - 2 x} {Sr}_{1 + 2 x} {Mn}_{2} O_{7}$ [44], respectively. The $q$ dependence of $γ$ is shown in the inset. The sky blue dotted line shows $γ$ for ${Mn}_{90} {Cu}_{10}$ [45]. (b) $ℏ ω$ dependence of the local spin susceptibility $Im χ (ℏ ω)$ . The black solid line is a guide to the eyes. The arrow represents the gap energy $Δ$ .
Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Damped spin-wave excitations in the itinerant antiferromagnet $γ − {Fe}_{0.7} {Mn}_{0.3}$

S. Ibuka, S. Itoh, T. Yokoo, and Y. Endoh

Phys. Rev. B 95, 224406 – Published 5 June 2017

Abstract

Physics Subject Headings (PhySH)

Authors & Affiliations

Article Text (Subscription Required)

References (Subscription Required)

Issue

Access Options

Physical Review B

covering condensed matter and materials physics

Damped spin-wave excitations in the itinerant antiferromagnet γ−Fe0.7Mn0.3

S. Ibuka, S. Itoh, T. Yokoo, and Y. Endoh

Phys. Rev. B 95, 224406 – Published 5 June 2017

Abstract

Physics Subject Headings (PhySH)

Authors & Affiliations

Article Text (Subscription Required)

References (Subscription Required)

Issue

Access Options

Authorization Required

Other Options

Download & Share

Images

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Log In

Search

Article Lookup

Paste a citation or DOI

Enter a citation

Damped spin-wave excitations in the itinerant antiferromagnet $γ − {Fe}_{0.7} {Mn}_{0.3}$