Nature of reentrant state in Cr75−xFe25+xCr75−xFe25+x (x=0, 5) thin films

• Spin-glass-like critical slowing down behavior in the reentrant (RE) state.
• Spin glass dynamic scaling associated with the transition to the RE state.
• AC driving-field-induced frequency shifts characteristic of spin glass behavior.
• Spontaneous magnetization in the RE state symptomatic of long-range FM order.
• Coexistence of spin glass order with long-range FM order in the reentrant state.

Real (χn′) and imaginary (χn″) components of the linear (n  =1) and nonlinear (n=2,3,4,5n=2,3,4,5) magnetic susceptibilities for the Cr75−xFe25+xCr75−xFe25+x (x=0, 5) thin films have been measured over three decades of ac driving-field frequency in the presence or absence of superposed dc magnetic fields (Hdc) at temperatures embracing the critical regions near the ferromagnetic (FM)–paramagnetic (PM) and reentrant (RE) phase transitions. The temperature, TRE, which marks the onset of the transition to the RE state, manifests itself as a shoulder in the χ1′(T) curve. The frequency- and Hdc-induced shifts in TRE and the dynamic scaling of χ1″(T) at temperatures T≲TRET≲TRE, characteristic of a spin glass (SG) state, have been observed. Concomitant with this SG-like behavior, a long-range FM order persists down to the lowest temperature in the RE region, as evidenced by the existence of experimental signatures, symptomatic of a FM state, such as spontaneous magnetization and the characteristic features in χ2′(T) and χ3′(T) at T≲TRET≲TRE. In the RE state, the Cr75−xFe25+xCr75−xFe25+x thin films are, thus, endowed with the characteristic attributes of both a conventional ferromagnet and a spin glass.