Magnetic phase diagram of K2Cr8O16 clarified by high-pressure muon spin spectroscopy

Ola Kenji Forslund,Daniel Andreica,Zurab Guguchia,Oscar Tjernberg,Hiroshi Nozaki,Hidenori Takagi,Zurab Shermadini,Izumi Umegaki,Yutaka Ueda,Rustem Khasanov,Yasmine Sassa,Martin Månsson,Jun Sugiyama,Masahiko Isobe,Viktor Jonsson,Elisabetta Nocerino

doi:10.1038/s41598-018-37844-5

Abstract

The K2Cr8O16 compound belongs to a series of quasi-1D compounds with intriguing magnetic properties that are stabilized through a high-pressure synthesis technique. In this study, a muon spin rotation, relaxation and resonance (μ+SR) technique is used to investigate the pressure dependent magnetic properties up to 25 kbar. μ+SR allows for measurements in true zero applied field and hereby access the true intrinsic material properties. As a result, a refined temperature/pressure phase diagram is presented revealing a novel low temperature/high pressure (pC1 = 21 kbar) transition from a ferromagnetic insulating to a high-pressure antiferromagnetic insulator. Finally, the current study also indicates the possible presence of a quantum critical point at pC2 ~ 33 kbar where the magnetic order in K2Cr8O16 is expected to be fully suppressed even at T = 0 K.

Highlights

Low dimensional magnets represent model materials, in which an intertwinning between electronic degrees of freedom leads to strongly correlated ground states[1,2,3]
While Cr3+ is considered to be very stable, only a few compounds display the Cr4+ state since it is only stabilized under extreme conditions[21]. This requires the synthesis and growth of the compound to be performed under high pressures (~6.7 GPa) resulting in very limited sample size/amount (100– 500 mg), which clearly limits the range of experimental methods available to study its intrinsic physical properties
While the FM phase appearing below TC = 180 K is well understood through the double exchange mechanism of itinerant d-electrons[14], the microscopic mechanism behind the metal-insulator transition (MIT) has been a great puzzle for many physicists

Summary

Introduction

Low dimensional magnets represent model materials, in which an intertwinning between electronic degrees of freedom leads to strongly correlated ground states[1,2,3]. Much attention has been paid to investigate the magnetic ground states of hollandite type materials[4,5,6,7,8,9] While Cr3+ is considered to be very stable, only a few compounds display the Cr4+ state since it is only stabilized under extreme conditions[21] This requires the synthesis and growth of the compound to be performed under high pressures (~6.7 GPa) resulting in very limited sample size/amount (100– 500 mg), which clearly limits the range of experimental methods available to study its intrinsic physical properties. Both zero-field (ZF) and weak-transverse field (wTF) field configurations were used and provided crucial information for clarifying and revealing a new magnetic phase diagram for this complex compound

Methods

Results

Conclusion