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The magnetic glassy state is a fascinating phenomenon, which results from the kinetic arrest of the first order magnetic phase transition. Interesting properties, such as metastable magnetization and nonequilibrium magnetic phases, are naturally developed in the magnetic glassy state. Here, we report magnetic glass property in the low spin state of Co3+ in EuBaCo2O5+{\delta} ({\delta} = 0.47) cobaltite at low temperature (T < 60 K). The measurements of magnetization under the cooling and heating in unequal fields, magnetization relaxation and thermal cycling of magnetization show the kinetic arrest of low magnetization state below 60 K. The kinetically arrested low temperature magnetic phase is further supported through the study of isothermal magnetic entropy, which shows the significant entropy change. The present results will open a new window to search the microscopic relation between the spin state transitions and the kinetic arrest induced magnetic glassy phenomena in complex materials.

This is a Comment on Kundhikanjana et al PRL 115 (2015) 265701 and the earlier Kundhikanjana et al arXiv:1306.3065v1 (2013), Comment: Phase Separation is due to Kinetic Arrest

Exchange bias is often observed when anti-ferromagnetic and ferromagnetic phases coexist. The coexistence of two competing magnetic phases can persist to the lowest temperatures if the disorder-broadened 1st order transition separating them is interrupted, as is proposed in the kinetic arrest phenomenon. The fractions of coexisting phases can, in this phenomenon, be tuned by following different cooling protocols. We discuss predicted behaviours of exchange bias resulting from the kinetic arrest phenomenon. Specifically, for appropriate values of cycling field Hmax and measuring temperature T0 there will be no exchange bias under cooling in zero field, while it will manifest with increasing cooling field, and then saturate., Comment: 8 pages, manuscript discusses dependence of exchange bias on cooling field in case of kinetic arrest

Metallic glasses are formed by splat-cooling; this ensures that atomic motions are arrested before the latent heat of solidification can be extracted. Glass is defined as a higher disorder metastable state with arrested kinetics. Arrested kinetics is a defining property of a glass, rather than structural disorder as, e.g., in amorphous silicon [1]. `Magnetic glasses' identified recently possess structural as well as magnetic long-range order, but show relaxation and specific heat as for a structural glass [1]. The values of Tc and Tg in these materials are easily varied by varying the magnetic field H, allowing one to go from metallic glass to glass former like scenario., Comment: Last paragraph of v2 is modified and expanded to address how studies on magnetic glass can help understand the physics of formation of structural glass, as distinct from jamming