Ultrasonic velocities have been measured and used to determine the elastic moduli of the highly magnetostrictive compounds: TbFe2, TbFe3, and ErFe2. A huge ΔE effect of 90% has been calculated for TbFe2 from our static stress-strain data.

Magnetization and magnetic torque measurements were made on single crystals of ErFe2 from 77°K to 329°K. From these measurements the magnetocrystalline anisotropy constants were deduced. At room temperature K1 = −3.3 × 106 ergs/cm3; at 77°K, −K1 > 108 ergs/cm3. Huge magnetic anisotropies are predicted for TbFe2 and DyFe2, whereas small anisotropies are predicted for ternary TbxDy1−xFe2 compounds near x = 0.3. The magnetostriction in this compound saturates easily indicating low anisotropy.

Unusually large magnetostrictions at room temperatures characterize the TbFe2region of the TbxFe1-xalloy system (x ranges from zero to one). We have measured the room temperature magnetostriction of various members of this system. The temperature dependence of the magnetostriction in TbFe2and ErFe2shows good agreement with single ion theory. The room temperature magnetostriction of TbFe2as was found to be 2940×10-6whereas it is 5100×10-6at 0 K for TbFe2and -2200×10-6at 0 K for ErFe2.

Huge magnetically induced strains (\ensuremath{\sim}0.2%) were observed in cubic Tb${\mathrm{Fe}}_{2}$ at room temperature. An anomalous "positive" temperature dependence for the magnetostriction is found for Dy${\mathrm{Fe}}_{2}$, yielding a peak in the magnetostriction exceeding 600 \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}6}$ above room temperature. The source of the magnetostriction is the large strain-dependent anisotropy of the rare-earth ion situated at the cubic sites in the $R{\mathrm{Fe}}_{2}$ lattice. The magnetoelastic energy of the rare-earth ions in these compounds is estimated to be 2 to 5 times larger than that of the rare-earth elements themselves.

Magnetization and magnetic anisotropy measurements were made on single crystals of ErFe2 from 77°K to room temperature. The magnetic anisotropy is much larger than any previously reported for cubic metals. Based upon these measurements the magnetic anisotropies of the Laves phase RFe2 compounds (R = Tb, Dy, Ho and Tm) were predicted.

The magnetization of single-crystal ytterbium orthoferrite (YbFeO3) was measured from 4.2° to 300°K in fields1 up to 110 kOe. At high temperatures a small spontaneous moment appears along the c direction. The magnetization is proportional to field along the a, b, and c directions. As the temperature is lowered, the field-dependent magnetization parallel to a increases rapidly and approaches a saturation value of 3.2 μb at 4.5°K. Along the c direction, an anomalously small increase in spontaneous magnetization with decreasing temperature is observed below 100°K. In addition, below 2.3°K the magnetization becomes temperature independent but still retains a large field dependence. From this we predict that either: (1) the magnetic unit cell is larger than the crystallographic cell, yielding Yb magnetic sublattices canted from the c direction; or (2) the Yb3+ ground state is not a Kramers doublet widely separated from the remaining levels. The high-field magnetization along the b directions is markedly smaller than that along a. It appears that the driving force for the magnetization reorientation is a huge rare-earth anisotropy, which tends to align the Yb spins along the a axis, along with the net iron magnetization. It is possible to explain our recent low-temperature magnetostriction measurements on YbFeO3, where a sizeable change in length is found for H ∥ a and H ∥ c, whereas a small magnetostriction is observed for H ∥ b.

Magnetostriction measurements have been made on single crystals of YbFeO3 in fields up to 105 kOe. At room temperature, the fractional changes in length along the crystallographic a, b and c directions are less than 0.2 x 10-6 at 35 kOe and 1.5 x 10-6 at 105 kOe. At 4.7 °K , because of the Yb3+ contribution, the magnetostriction parallel to a is large and predominantly single-ion like. Magnetization measurements made over the same temperature and field ranges reveal a huge anisotropic magnetization with paramagnetic saturation of the rare earth sublattice parallel to a.

Magnetostriction oscillations of de Haas---van Alphen origin are observed in $p$-type PbTe, a single-band multivalley semiconductor. The hole concentration of the material studied is 3\ifmmode\times\else\texttimes\fi{}${10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. The amplitude of the oscillations is related not only to the usual shear deformation potential ${\ensuremath{\Xi}}_{u}$, which causes intervalley charge transfer as the valleys rigidly shift relative to each other in energy, but also to six strain masses, which describe rotations and distortions of the hole valleys.

Certain thin Permalloy films which have a basically uniaxial character show square hysteresis loops in both easy and hard direction. The hard-direction coercivity H_{c2} is about half that of the easy direction. If a saturating magnetic field is applied at an angle α, a few degrees from the hard direction, a loop typical of uniaxial films results. Application of a small bias field normal to the drive field results in a triangular loop. This has two stable remanent states, in the first of which the magnetization has been left in a hard-direction low-permeability zero state. The other remanent state has the magnetization in a high permeability, easy direction, the one state. Whether the interrogating pulses of magnitude less than H_{c2} will result in an output pulse or not depends on the state of the device. No destruction of the stored information occurs. It is possible to write into either state by using the coincident current techniques, as long as precautions are taken against creep from the hard direction.

The polycrystalline saturation magnetostriction λs and volume magnetostriction δω/δH of some thirty types of commercial ferrite memory cores have been measured. A capacitance technique sufficiently sensitive to measure elongations of ∼0.1 Å and Δl/l of ∼3×10−8 was employed, and λs was determined by rotation of the saturated moment through 90°, λs values between −1×10−7 to −1×10−5 and λω/λH values from −1×10−10 to −7×10−10 Oe−1 were obtained. Since these magnetostriction constants measure coupling of magnetization and dimensional parameters, the data reflects a wide range of core sensitivity to stress-induced demagnetization and ``magnetostrictive ringing'' of cores upon switching.

Measurements of the elastic constants and thermal expansion of PbTe have been made from 4.2° to 303.2°K. The extrapolated 0°K values for C44, (C11−C12)/2, and (C11+2C12)/3, respectively, are 1.514±0.009, 6.184±0.066, and 4.560±0.042×1011 dyn/cm2. At 303.2°K these values are 1.344±0.008, 5.016±0.057, and 4.107±0.037×1011 dyn/cm2. Intermediate values are presented graphically, as are the thermal-expansion data. The linear coefficient of thermal expansion is found to be 20.4±0.4×10−6/°C at room temperature. The 0°K Debye temperature is calculated to be 176.7°±0.5°K.

Received 25 September 1967DOI:https://doi.org/10.1103/PhysRevLett.19.1428©1967 American Physical Society