Magnetic imaging of a supercooling glass transition in a weakly disordered ferromagnet

Abstract

Spin glasses are founded in the frustration and randomness of microscopic magnetic interactions. They are non-ergodic systems where replica symmetry is broken. Although magnetic glassy behaviour has been observed in many colossal magnetoresistive manganites, there is no consensus that they are spin glasses. Here, an intriguing glass transition in (La,Pr,Ca)MnO3 is imaged using a variable-temperature magnetic force microscope. In contrast to the speculated spin-glass picture, our results show that the observed static magnetic configuration seen below the glass-transition temperature arises from the cooperative freezing of the first-order antiferromagnetic (charge ordered) to ferromagnetic transition. Our data also suggest that accommodation strain is important in the kinetics of the phase transition. This cooperative freezing idea has been applied to structural glasses including window glasses and supercooled liquids, and may be applicable across many systems to any first-order phase transition occurring on a complex free-energy landscape.

Conversion of a glassy antiferromagnetic-insulating phase to an equilibrium ferromagnetic-metallic phase by devitrification and recrystallization in Al substituted Pr0.5Ca0.5MnO3

“…10 ). We stress that the CHUF measurements not only allows to identify both the existence and magnetic order of the 'magnetic glassy' state but goes deeper to probe correlation between T* and T K without taking recourse to time domain 16 .…”

Kinetic-arrest-induced phase coexistence and metastability in(Mn,Fe)2(P,Si)

“…The first-order phase transition is characterized by a discontinuous change in the first derivative of the free energy (e.g., magnetization M, entropy S, and volume V ) triggered by thermodynamic variables (e.g., temperature T , magnetic field H , and pressure P ). Intrinsic composition disorder broadens the first-order phase transition, causing a coexistence of transformed and untransformed phases over the phase transition region, as indicated by different nano-and microscale techniques [7][8][9][10][11][12]. After crossing the phase transition region, the system reaches an equilibrium state with a homogeneous phase.…”

Impact of nanostructuring on the magnetic and magnetocaloric properties of microscale phase-separated La5/8−yPryCaBingham1, Lampen2, Phan3 et al. 2012Phys. Rev. B

“…We note that these studies of grain size reduction in polycrystalline LPCMO have not crossed the ~100nm threshold, below which surface effects dominate the physics of manganite nanoparticles. 43 With the exception of our previous study on a closely related composition, 10 we find that despite wealth of available literature on thin films, [29][30][31][32][33][34][35][36][37]41 single- 19,22,25,26,28,40 and polycrystalline 8,9,14,17,18,20,21,23,24,45 forms of LPCMO, virtually no work has been done on nanoparticles of the same compounds, although reduction of particle size to well below the characteristic phase separation length can be expected to have a great impact on strain, and consequently on the magnetic properties of the system. 10 Adding an additional layer of interest, opposing surface-driven trends are observed in nanosized FM and CO compounds.…”