Abstract
In this work we create in 10 M Ni-Mn-Ga martensitic samples special martensitic variant structures consisting of only three twins separated by two a/c twin boundaries: Type I and Type II, with relatively low and very high mobility, respectively. The “domain engineered” structure thus created allows us to investigate the dynamics of a single highly mobile a/c twin boundary (TB). We show that temperature variations between 290 and 173 K in our samples induce an intense transitory internal friction at ultrasonic frequencies ca. 100 kHz, peaking around 215 K. A comparison is made of the data for the “domain engineered” sample with the behaviour of reference samples without a/c TB. Reference samples have two different orientations of a/b twins providing zero and maximum shear stresses in a/b twinning planes. We argue, first, that the transitory internal friction, registered at rather high ultrasonic frequencies, has magnetic origin. It is related with the rearrangement of magnetic domain structure due to the motion of a/c twin boundary induced by thermal stresses. This internal friction term can be coined “magnetic transitory internal friction”. Magnetic transitory internal friction is a new category, linking the classes of transitory and magnetomechanical internal friction. Second, the structure of a/b twins is strongly non-equilibrium over a broad temperature range. As a consequence, the Young’s modulus values of the samples with maximum shear stress in a/b twinning planes can take any value between ca. 15 and 35 GPa, depending on the prehistory of the sample.
Highlights
10 M Ni-Mn-Ga martensites are examples of a multiferroic material in which strong coupling between ferroic subsystems—elastic and magnetic—is responsible for such useful property as magnetic actuation
Of the strain amplitude; - a strong difference between direct run and reverse run; we will refer to this effect as strain amplitude hysteresis; - the strain amplitude hysteresis is well reproducible in two consecutive strain amplitude scans: it fully recovers in the second scan
In general terms of anelasticity of solids, present experiments evidence the existence of the ultrasonic transitory internal friction of magnetic origin
Summary
10 M Ni-Mn-Ga martensites are examples of a multiferroic material in which strong coupling between ferroic subsystems—elastic and magnetic—is responsible for such useful property as magnetic actuation. We observe and describe a new phenomenon, associated with local magnetic flux change provoked by the motion of an elastic domain wall—a/c twin boundary (TB). This new phenomenon is the ultrasonic transitory internal friction (IF) of magnetic origin which is a new category of damping, linking the classes of transitory and magnetomechanical IF. In our experiments we use the “domain engineered” 10 M Ni-Mn-Ga samples with controlled structure of a/c and a/b twins. Such experiments reveal new striking features of apparent elastic properties of a/b twin laminate
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