Cubic magnets with Dzyaloshinskii-Moriya interaction at low temperature

Journal Article · Mon May 01 00:00:00 EDT 2006 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PHYSREVB.73.1· OSTI ID:20788162

Maleyev, S V ^[1]

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1. Petersburg Nuclear Physics Institute, Gatchina, St. Petersburg 188300 (Russian Federation)

Magnetic properties of noncentrosymmetric cubic helimagnets (MnSi, etc.) at low T are studied theoretically using conventional exchange, Dzyaloshinskii-Moriya interaction, anisotropic exchange and magnetic dipolar interaction. Structure in magnetic field and spin-wave spectrum are considered. In low field g{mu}{sub B}H{sub 1}={delta}{radical}(2), where {delta} is the spin-wave gap, the helix axis k turns along the field. A transition to ferromagnetic state occurs at g{mu}{sub B}H{sub c}=Ak{sup 2}, where A is the spin-wave stiffness at momenta q>>k. It is observed that the spin-wave spectrum is strongly anisotropic: excitations with q parallel k and q perpendicular k have linear and quadratic dispersion at q<<k respectively if one neglects the gap {delta}. This is a result of umklapp interaction connecting the spin-waves with momenta q and q{+-}k. This interaction leads to infinite set of equations for the Green functions. The simplest n=1 approximation is applicable at q=0 and q>>k. Further n=2 approximation gives correct result at q<<k. Results of both approximations are qualitative at q{approx}k. The weak field (H<H{sub 1}) perpendicular to k deforms the helix and the second harmonics of the spin rotation appears. The spin-wave gap is a result of the spin-wave interaction considered in the Hartree-Fock approximation and cubic anisotropy. Properties of the ESR and neutron scattering are considered. The theoretical results are in agreement with existing experimental data.

• OSTI ID: 20788162
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Vol. 73, Issue 17; Other Information: DOI: 10.1103/PhysRevB.73.174402; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ABSORPTION SPECTRA
ANISOTROPY
ELECTRON SPIN RESONANCE
ELECTRONS
EXCHANGE INTERACTIONS
EXCITATION
FERROMAGNETIC MATERIALS
GREEN FUNCTION
HARTREE-FOCK METHOD
MAGNETIC FIELDS
MAGNETIC MOMENTS
MAGNETIC PROPERTIES
MANGANESE ALLOYS
MANGANESE SILICIDES
NEUTRON DIFFRACTION
PARAMAGNETISM
PERMANENT MAGNETS
RESONANCE NEUTRONS
ROTATION
SILICON ALLOYS
SPIN WAVES
TEMPERATURE DEPENDENCE
UMKLAPP PROCESSES