TY - JOUR
T1 - Surface Magnons and Surface Spin Arrangements in Heisenberg Magnets with Two Kinds of Exchange Interactions
AU - Harada, Isao
AU - Nagai, Ojiro
PY - 1977/1/1
Y1 - 1977/1/1
N2 - Acoustic surface-magnon spectra are calculated for semi-infinite ferro- and antiferromagnets, where spins are coupled via exchange interactions both with nearest neighbors (J1) and with next-nearest neighbors (J2). It is found that, when the parameter α=J2/|J1| lies in certain intervals, the surface-magnon frequency is negative or imaginary, although the bulk-magnon frequencies remain real and positive. This condition indicates that the uniform ferro- or antiferromagnetic spin arrangement is not stable. For several cases of this type, it is shown that a nonuniform spin arrangement, characterized by a rearrangement of spins in the surface region, has a lower classical spin-ordering energy than the uniform state, and hence is stable. In various cases, various different arrangements of surface spins are found to be stable, including a helical arrangement, in which spins in the surface region are ordered with helical symmetry while bulk spins are in an antiferromagnetic state.
AB - Acoustic surface-magnon spectra are calculated for semi-infinite ferro- and antiferromagnets, where spins are coupled via exchange interactions both with nearest neighbors (J1) and with next-nearest neighbors (J2). It is found that, when the parameter α=J2/|J1| lies in certain intervals, the surface-magnon frequency is negative or imaginary, although the bulk-magnon frequencies remain real and positive. This condition indicates that the uniform ferro- or antiferromagnetic spin arrangement is not stable. For several cases of this type, it is shown that a nonuniform spin arrangement, characterized by a rearrangement of spins in the surface region, has a lower classical spin-ordering energy than the uniform state, and hence is stable. In various cases, various different arrangements of surface spins are found to be stable, including a helical arrangement, in which spins in the surface region are ordered with helical symmetry while bulk spins are in an antiferromagnetic state.
UR - http://www.scopus.com/inward/record.url?scp=3342920652&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=3342920652&partnerID=8YFLogxK
U2 - 10.1143/JPSJ.42.738
DO - 10.1143/JPSJ.42.738
M3 - Article
AN - SCOPUS:3342920652
VL - 42
SP - 738
EP - 748
JO - Journal of the Physical Society of Japan
JF - Journal of the Physical Society of Japan
SN - 0031-9015
IS - 3
ER -