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Cooling field and temperature dependent exchange bias in spin glass/ferromagnet bilayers.

Rui WB, Hu Y, Du A, You B, Xiao MW, Zhang W, Zhou SM, Du J - Sci Rep (2015)

Bottom Line: Significantly, increasing in the magnitude of HFC reduces (increases) the value of HE in the negative (positive) region, resulting in the entire HE∼T curve to move leftwards and upwards.In the meanwhile, HFC variation has weak effects on HC.Thus this work reveals that the SG/FM bilayer system containing intimately coupled interface, instead of a single SG layer, is responsible for the novel EB properties.

View Article: PubMed Central - PubMed

Affiliation: National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, P. R. China.

ABSTRACT
We report on the experimental and theoretical studies of cooling field (HFC) and temperature (T) dependent exchange bias (EB) in FexAu1-x/Fe19Ni81 spin glass (SG)/ferromagnet (FM) bilayers. When x varies from 8% to 14% in the FexAu1-x SG alloys, with increasing T, a sign-changeable exchange bias field (HE) together with a unimodal distribution of coercivity (HC) are observed. Significantly, increasing in the magnitude of HFC reduces (increases) the value of HE in the negative (positive) region, resulting in the entire HE∼T curve to move leftwards and upwards. In the meanwhile, HFC variation has weak effects on HC. By Monte Carlo simulation using a SG/FM vector model, we are able to reproduce such HE dependences on T and HFC for the SG/FM system. Thus this work reveals that the SG/FM bilayer system containing intimately coupled interface, instead of a single SG layer, is responsible for the novel EB properties.

No MeSH data available.


Related in: MedlinePlus

(a) Calculated interfacial exchange energy density (εIF) during the magnetizing process at T = 2.6 K after cooling under HFC = 0.2 kOe and 50 kOe, where solid symbols-solid lines and open symbols-dot lines correspond to the descending and ascending branches of the M-H hysteresis loops and arrows indicate the magnetizing directions. (b) Calculated energy barriers (Eb) of the SG spins at the interface at T = 2.6 K after the field cooling process and before the isothermally magnetizing. (c) Calculated x component (μx) of the SG magnetic moments at the interface under H = −5 kOe during the magnetizing process at T = 2.6 K. (d) Schematic illustrations of the energy versus phase-space coordinate during the magnetization reversal at the ascending branch of the M-H hysteresis loops.
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f5: (a) Calculated interfacial exchange energy density (εIF) during the magnetizing process at T = 2.6 K after cooling under HFC = 0.2 kOe and 50 kOe, where solid symbols-solid lines and open symbols-dot lines correspond to the descending and ascending branches of the M-H hysteresis loops and arrows indicate the magnetizing directions. (b) Calculated energy barriers (Eb) of the SG spins at the interface at T = 2.6 K after the field cooling process and before the isothermally magnetizing. (c) Calculated x component (μx) of the SG magnetic moments at the interface under H = −5 kOe during the magnetizing process at T = 2.6 K. (d) Schematic illustrations of the energy versus phase-space coordinate during the magnetization reversal at the ascending branch of the M-H hysteresis loops.

Mentions: Based on the consistent HE results between experiment and simulation, we interpret the above experimental phenomena relying on our simulation method. At first, we have excluded that the EB phenomena in the SG/FM bilayers depend solely on interfaces [see Supplementary Material A]. In other words, the configurations/spins inside the SG influence the FM spins through the SG/FM interface and the SG/FM interface itself also plays a significant role in establishing EB. Thus in the low T region, we calculate the interfacial exchange energy density (εIF) to interpret the relative EB behavior, which can be expressed aswhere is the interfacial coupling stength between the FM and SG spins, A is the interface area and μ denotes the magnetic moment of the interfacial spin belonging to the FM or SG. Since this is the dominant energy term influencing the HE in SG/FM bilayers and meanwhile a low enough T will suppress thermal fluctuation, the change of εIF mainly determines the evolution of spin configuration at the interface during isothermally magnetizing at low T. Therefore, it provides us the opportunity to image the M-H behaviors microscopically and helps us to elucidate how HE is influcenced by HFC. Figure 5(a) shows the results calculated for T = 2.6 K. In addition, other parameters including the spin energy barrier and the x component of spin under specific fields are calculated simultaneously in order to provide a clear physical picture during isothermally magnetizing at low T, with the results shown in Fig. 5 (b,c), respectively.


Cooling field and temperature dependent exchange bias in spin glass/ferromagnet bilayers.

Rui WB, Hu Y, Du A, You B, Xiao MW, Zhang W, Zhou SM, Du J - Sci Rep (2015)

(a) Calculated interfacial exchange energy density (εIF) during the magnetizing process at T = 2.6 K after cooling under HFC = 0.2 kOe and 50 kOe, where solid symbols-solid lines and open symbols-dot lines correspond to the descending and ascending branches of the M-H hysteresis loops and arrows indicate the magnetizing directions. (b) Calculated energy barriers (Eb) of the SG spins at the interface at T = 2.6 K after the field cooling process and before the isothermally magnetizing. (c) Calculated x component (μx) of the SG magnetic moments at the interface under H = −5 kOe during the magnetizing process at T = 2.6 K. (d) Schematic illustrations of the energy versus phase-space coordinate during the magnetization reversal at the ascending branch of the M-H hysteresis loops.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4562234&req=5

f5: (a) Calculated interfacial exchange energy density (εIF) during the magnetizing process at T = 2.6 K after cooling under HFC = 0.2 kOe and 50 kOe, where solid symbols-solid lines and open symbols-dot lines correspond to the descending and ascending branches of the M-H hysteresis loops and arrows indicate the magnetizing directions. (b) Calculated energy barriers (Eb) of the SG spins at the interface at T = 2.6 K after the field cooling process and before the isothermally magnetizing. (c) Calculated x component (μx) of the SG magnetic moments at the interface under H = −5 kOe during the magnetizing process at T = 2.6 K. (d) Schematic illustrations of the energy versus phase-space coordinate during the magnetization reversal at the ascending branch of the M-H hysteresis loops.
Mentions: Based on the consistent HE results between experiment and simulation, we interpret the above experimental phenomena relying on our simulation method. At first, we have excluded that the EB phenomena in the SG/FM bilayers depend solely on interfaces [see Supplementary Material A]. In other words, the configurations/spins inside the SG influence the FM spins through the SG/FM interface and the SG/FM interface itself also plays a significant role in establishing EB. Thus in the low T region, we calculate the interfacial exchange energy density (εIF) to interpret the relative EB behavior, which can be expressed aswhere is the interfacial coupling stength between the FM and SG spins, A is the interface area and μ denotes the magnetic moment of the interfacial spin belonging to the FM or SG. Since this is the dominant energy term influencing the HE in SG/FM bilayers and meanwhile a low enough T will suppress thermal fluctuation, the change of εIF mainly determines the evolution of spin configuration at the interface during isothermally magnetizing at low T. Therefore, it provides us the opportunity to image the M-H behaviors microscopically and helps us to elucidate how HE is influcenced by HFC. Figure 5(a) shows the results calculated for T = 2.6 K. In addition, other parameters including the spin energy barrier and the x component of spin under specific fields are calculated simultaneously in order to provide a clear physical picture during isothermally magnetizing at low T, with the results shown in Fig. 5 (b,c), respectively.

Bottom Line: Significantly, increasing in the magnitude of HFC reduces (increases) the value of HE in the negative (positive) region, resulting in the entire HE∼T curve to move leftwards and upwards.In the meanwhile, HFC variation has weak effects on HC.Thus this work reveals that the SG/FM bilayer system containing intimately coupled interface, instead of a single SG layer, is responsible for the novel EB properties.

View Article: PubMed Central - PubMed

Affiliation: National Laboratory of Solid State Microstructures and Department of Physics, Nanjing University, Nanjing 210093, P. R. China.

ABSTRACT
We report on the experimental and theoretical studies of cooling field (HFC) and temperature (T) dependent exchange bias (EB) in FexAu1-x/Fe19Ni81 spin glass (SG)/ferromagnet (FM) bilayers. When x varies from 8% to 14% in the FexAu1-x SG alloys, with increasing T, a sign-changeable exchange bias field (HE) together with a unimodal distribution of coercivity (HC) are observed. Significantly, increasing in the magnitude of HFC reduces (increases) the value of HE in the negative (positive) region, resulting in the entire HE∼T curve to move leftwards and upwards. In the meanwhile, HFC variation has weak effects on HC. By Monte Carlo simulation using a SG/FM vector model, we are able to reproduce such HE dependences on T and HFC for the SG/FM system. Thus this work reveals that the SG/FM bilayer system containing intimately coupled interface, instead of a single SG layer, is responsible for the novel EB properties.

No MeSH data available.


Related in: MedlinePlus