Title: Magnetic structure and magnetization of helical antiferromagnets in high magnetic fields perpendicular to the helix axis at zero temperature

Abstract

The zero-temperature angles of magnetic moments in a helix or sinusoidal fan confined to the x y plane, with respect to an in-plane magnetic field H _x applied perpendicular to the z axis of a helix or fan, are calculated for commensurate helices and fans with field-independent turn angles k d between moments in adjacent layers of the helix or fan using the classical J ₀ - J ₁ - J ₂ Heisenberg model. For 0 < k d < 4 π / 9 , first-order transitions from helix to a fan structure occur at fields H t as previously inferred, where the fan is found to be approximately sinusoidal. However, for 4 π / 9 ≤ k d ≤ π , different behaviors are found depending on the value of k d and these properties vary nonmonotonically with k d . In this k d range, the change from helix to fanlike structure is usually a crossover with no phase transition between them, although first-order transitions are found for k d = 3 π / 5 and 8 π / 11 and a second-order transition for k d = 3 π / 4 . At a critical field Hmore » _c , the fan or fanlike structures exhibit a second-order transition to the paramagnetic state. The H _c for a helix undergoing a field-induced change to a fan or fanlike structure is found to be the same as for a sinusoidal fan with the same k d and interlayer interactions. We present analytical expressions for H _c versus k d. We also calculated the average x -axis moment per spin μ _{x ave} versus H _x for helices and fans with crossovers and phase transitions between them. When smooth helix to fanlike crossovers occur in the range 4 π / 9 ≤ k d ≤ π , μ _{x ave} exhibits an S-shape behavior with increasing H _x . The behavior we predict is consistent with μ _{x ave} ( H _x ) data previously reported by Sangeetha et al. [Phys. Rev. B 94, 014422 (2016)] for single-crystal EuCo ₂ P ₂ possessing a helix ground state with k d ≈ 0.85 π . The low-field magnetic susceptibility and the ratio H _t / H _c are calculated analytically or numerically versus k d for helices, and are shown to approach the respective known limits for k d → 0 .« less

Authors:

Johnston, David ^[1]

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+ Show Author Affiliations

1. Ames Lab. and Iowa State Univ., Ames, IA (United States). Dept. of Physics

Publication Date:

Tue Sep 05 00:00:00 EDT 2017

Research Org.:

Ames Lab., Ames, IA (United States)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1394804

Alternate Identifier(s):

OSTI ID: 1378398

Report Number(s):

IS-J-9439
Journal ID: ISSN 2469-9950; PRBMDO; TRN: US1702839

Grant/Contract Number:  

AC02-07CH11358

Resource Type:

Accepted Manuscript

Journal Name:

Physical Review B

Additional Journal Information:

Journal Volume: 96; Journal Issue: 10; Journal ID: ISSN 2469-9950

Publisher:

American Physical Society (APS)

Country of Publication:

United States

Language:

English

Subject:

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; 75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY