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    Key role of high-Tc twinned martensitic materials to gain a magnetic actuation higher than 15%
    (Elsevier Science Sa, 2021) Sarli, Numan; Paran, Nejdet; Ablay, Gunyaz; Ocak, Hamza Y.; Yildiz, Yasin G.; Yildiz, Gokcen D.; Yagci, Nermin K.
    Twinning angle outcomes of the twinned martensitic (TM) and detwinned martensitic (DTM) structural transformations on the magnetic features of the austenite (A) parent phase are researched by using the effective field theory established by Kaneyoshi. The implementation of the effective field theory verifies that the shape memory mechanism occurs with phase transformations, A -> TM -> DTM -> A. It also shows that the austenite parent phase has two types of actuations: one-dimensional actuation (in only y-axis) for TM, and two-dimensional actuation (in x and y-axes) for DTM. Magnetic field-induced actuation (strain) in the range of 5-15% at twinning angle theta >= 120.816 degrees of TM and DTM is reported for some materials in the literature. On the other hand, in this work, it is estimated that a twinning angle lower than this twinning angle (i.e., theta < 120.816 degrees) must be achieved to have a strain higher than 15%. We also suggest that materials with higher magnetization, Curie temperature, coercive field and remanence magnetization should be taken into account to get a strain higher than 15%, since all these features are directly affected by the twinning angle (theta). Our results on Curie temperature (T-c) match with the experimental results of Ni49.8Mn28.5Ga21.7 (achieved 6% strain) with T-c = 95 degrees C (368 K) by Murray et al., and Ni46Mn24Ga22Co4Cu4 with T-c = 393 K (achieved 12% strain) by Sozinov et al. (C) 2021 Elsevier B.V. All rights reserved.
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    Magnetic properties of the Martensitic transformations with twinned and detwinned
    (Elsevier Science Bv, 2019) Sarli, Numan; Yildiz, Gokcen Dikici; Yildiz, Yasin Gokturk; Yagci, Nermin Kahveci
    The effects of the Austenite (A), twinned Martensite (TM) and detwinned Martensite (DTM) structural transformations on the ferromagnetic properties are investegated by means of the effective field theory developed by Kaneyoshi. We find that the critical Curie temperature of the A, TM and DTM is obtained as T-c(A) < T-c(DTM)< T-c(TM) for H = 0. Thermal magnetization loops are obtained for H not equal 0. The area of the thermal magnetization loops of the A-TM is wider than those of the A-DTM. Paramagnetic Austenite has a phase transition from paramagnetic (PM) phase to ferromagnetic (FM) phase at T-c(TM) and T-c(DTM). The temperature of the As (Austenite start), TMf (twinned Martensite finish) and DTM f (detwinned Martensite finish) increase as the external magnetic field (H) increases. The magnetizations of the A, TM and DTM are the same at low temperature (T < A(s)). The coercive field points are obtained as H-c(A) < H-c(DTM)< H-c(TM). The shearing angle plays very important role in the structural transformations and their ferromagnetic properties, especially in TM.
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    Prediction of the Bain spin memory materials (BSMM) revealed by Kaneyoshi theory
    (TAYLOR & FRANCIS LTD, 2020) Saatci, Buket; Sarli, Numan; Dagdemir, Yilmaz; Yildiz, Yasin Gokturk; Ocak, Hamza Yasar
    In this work, we investigate the spin transformation from ferromagnetic austenite BCT lattice to antiferromagnetic martensite BCC lattice (j(i) = +J -> j(i) = -J or up arrow up arrow ->up arrow down arrow) in Bain transformation (or Bain strain) by using effective field theory which is developed by Kaneyoshi. We find that the spin orientation changes the magnetic properties in the Bain BCT -> BCC transformation. Therefore, we predict that material can memory their spin orientations in the austenite-martensite transformation similar to the shape memory effect in the shape memory materials. Since the austenite-martensite transformation mechanism is first modelled by Bain, we call this spin memory effect as 'Bain spin memory materials (BSMM)'.
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    Spin Induced Quantum Tunneling of the Magnetization
    (World Scientific Publ Co Pte Ltd, 2021) Yıldız, Gökçen Dikici; Yıldız, Yasin Göktürk; Sarli, Numan
    Quantum tunneling of the magnetization (QTM) of the spin-1/2 Vanadium-15 (V15) single molecular magnets (SMMs) is investigated by means of the effective field theory developed by Kaneyoshi. We deal with the two hexagon layers (shell, VS) and one triangular interlayer (core, VC) with the spin-1/2 Ising particles. We find that the V15 has a normal ferromagnetic hysteresis behavior for its all spins are up (parallel). However, V15 has a staircase-like hysteresis behavior that is the signature of the QTM for the spin-down orientation (antiparallel) of the core. QTM appears with the splitting of the magnetizations versus temperature (M-T) and external field (M-H) curves. Namely, QTM occurs from +m(VC1) to -m(VC2)(|m(VC1)|>|m(VC2)|) in the core, from +m(VS1) to +m(VS2) (|m(VS1)|>|m(VS2)|) in the shell (only mVS-H curves at T> 0.1) and from +M1(V15) to +M2(V15) (|M1V15|>|M2V15|) in the total V15. By considering these different splitting behaviors of the magnetizations of the shell, core and total V15 at TT-C, we suggest three different kinds of QTM: 1-ferromagnetic QTM (FMQTM) at TT-C for the shell, core and total V15 SMM. Moreover, it is found that there is a relationship between the QTM and type II and surface superconductivity. The EFT results of QTM in V15 are in good agreement with the other theoretical and experimental results of the V15 and other SMMs.