Field-Induced Transitions in Highly Frustrated SrHo2O4

Olga Young,Dmitry Khalyavin,Geetha Balakrishnan,Andrew Wildes,Pascal Manuel,Oleg Petrenko

doi:10.3390/cryst9100488

Olga Young, Dmitry Khalyavin + Show 4 more

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https://doi.org/10.3390/cryst9100488

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Abstract

SrHo 2O 4 is a geometrically frustrated magnet in which the magnetic Ho 3 + ions are connected through a network of zigzag chains and coupled by several competing interactions. The Ho 3 + ions show a pronounced Ising anisotropy at low temperatures, and the spins on the two crystallographically inequivalent magnetic sites point along orthogonal crystallographic axes. Using single-crystal neutron diffraction, we report on the development of complex and highly anisotropic short- and long-range magnetic order in SrHo 2O 4 induced by an applied magnetic field. For H ‖ c , the diffuse scattering around the k = 0 positions is suppressed and above 0.5 T the spin structure for one of the Ho sites is long-range and ferromagnetic. For H ‖ b , planes of diffuse scattering at Q = ( h k ± l 2 ) are split by the field, and an up–up–down magnetic order associated with a 1/3-magnetisation plateau develops at 0.8 T. Further increasing the field above 1.2 T allows the second Ho site to also order in a long-range ferromagnetic structure.

Highlights

Competing magnetic interactions are studied in frustrated magnetism, and, when these are incompatible with the geometry of the lattice, systems can find it hard to establish a unique ground state
SrHo2 O4, one of the members of a large family of the SrLn2 O4 (Ln = lanthanide) compounds, which contain magnetic atoms arranged in zig-zag ladders and all of which demonstrate the typical signs of magnetic frustration—reduced ordering temperatures, coexistence of different ground states and high sensitivity to external perturbations, such as an applied magnetic field
To the famous cases of the spin ice behaviour found in some pyrochlore compounds [2] where the rare earth Ho and Dy ions behave like Ising spins, the magnetic ions in some SrLn2 O4 compounds, including SrEr2 O4, SrDy2 O4 and SrHo2 O4, demonstrate strong single-ion anisotropy and could be described as Ising magnetic moments albeit with different easy-axis magnetisation directions for different sites

Summary

Introduction

Competing magnetic interactions are studied in frustrated magnetism, and, when these are incompatible with the geometry of the lattice, systems can find it hard to establish a unique ground state. A second type of diffuse scattering gradually appears as planes of scattering intensity at (hk ±2l )—showing that the unit cell for this magnetic structure is doubled along the c-axis. These planes are seen as “rods” of scattering intensity in both the (h0l ) and (0kl ) planes in reciprocal space at Q = (00 12 ) and symmetry related positions, even at 4.5 K [14]. The results of our measurements show that, at low temperatures, when a field is applied along the c-axis, the diffuse magnetic scattering that appears around positions with the propagation vector k = 0 in the (hk0) plane is suppressed, and that a phase transition to a fully polarised structure occurs above μ0 H = 0.4 T.

Experimental Details

Results and Discussion

Conclusions